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									              MASSAGE &
AND SPINAL NERVES                                                       ANDREW J. KUNTZMAN, PH.D., LMT
This course provides an introduction   This course focuses on aspects of the nervous system as it relates to muscles
to the anatomy and physiology of       and thus to the practice of massage therapy. When you finish this course you will
the spinal cord and spinal nerves.     be able to:
Because the control of muscles is      • Understand, through knowledge of nerve physiology, how massage therapy af-
affected primarily by the nervous        fects the functioning of the nervous system and its control of muscles.

system, this course describes cer-     • List six general effects of massage therapy on nervous tissue.
tain aspects of the nervous system     • Describe the processes of communication and repair in the CNS and PNS.
as it relates to muscles and to the    • List the areas in the body supported by plexuses and intercostals nerves.
practice of massage.                   • Describe the results of injuries to the brachial plexus and four other types of
                                         injuries common to nerves.
                                       • Describe two ways the spinal cord promotes homeostasis.
                                       • Describe the roles of muscle spindles and tendon organs.
                                       • List three common sites of injury to the spinal cord and effects of transections.
                                          OVERVIEW OF THE NERVOUS SYSTEM
                                          Nervous tissue is one of the four main tissue types. It acts together with the endocrine system to regulate homeo-
                                          stasis in the body. The nervous system has many similarities with the endocrine system, and they control of the
                                          activities of the body to keep it within optimal limits. However, the nervous system is extremely fast-acting, but
                                          shorter lived in action than the endocrine (hormonal) system. Think of how quickly you reflexively move when you
                                          accidentally put your hand on a hot stove or step on a tack.
                                             The nervous system uses a series of electrochemical signals to receive information from the receptors of the body
                                          in the peripheral nervous system (PNS) regions and sends them to the central nervous system (CNS), the brain and
                                          spinal cord, to coordinate our actions. A new message is then sent to an effector organ or muscle to take action. This
                                          whole process of sending information from receptor to coordinator to reactor takes only a fraction of a second. That
                                          would not sound so amazing, if not for the fact that this is happening at millions of places in the body at once.
                                             Nervous tissue monitors every body activity, including breathing, digestion and the beating of your heart. You
                                          do not even need to actively think about these things since they are done for you automatically (or autonomically)
                                          without your conscious thought. Certain of the manual therapies may utilize routine sensory, motor and reflex tests
                                          to assess the role of the nervous system in maintaining homeostasis.
                                             Even in this age of technology and computers, no computer built today can rival the complexity of the human
                                          nervous system. The nervous system is a network of billions of interconnected nerve cells (neurons) that receive
                                          stimuli, coordinate this sensory information and cause the body to respond appropriately. The individual neurons
                                          transmit messages by means of a complicated electrochemical process. With a mass of only 3 percent of the total
                                          body weight, the nervous system is one of the smallest yet most complex of the 11 body systems. The two main
                                          subdivisions of the nervous system are the central nervous system (CNS), which consists of the brain and spinal cord,
                                          and the peripheral nervous system (PNS), which includes all nervous tissue outside the CNS.
                                             The nervous system is also responsible for our perceptions, behaviors and memories, as well as initiating all vol-
                                          untary movements. Because the nervous system is quite complex, it’s commonly considered in several chapters of a
                                          typical textbook. We will consider the organization of the nervous system, the structure and functions of the spinal
                                          cord and spinal nerves, as well as certain applications to the manual therapies.

                                          STRUCTURES OF THE                        plexuses—that help regulate the di-       complex assortment of tasks, such
                                          NERVOUS SYSTEM                           gestive system. Sensory receptors are     as sensing smells, producing speech,
                                          The spinal cord connects to the brain,   dendrites of sensory neurons (such        remembering past events, provid-
                                          contains about 100 million neurons       as sensory receptors in the skin) or      ing signals that control body move-
                                          and is encircled by the bones of the     separate, specialized cells that moni-    ments and regulating the operation
                                          vertebral column. Emerging from          tor changes in the internal or exter-     of internal organs. These diverse ac-
                                          the spinal cord are 31 pairs of spinal   nal environment (such as photore-         tivities are grouped into three basic
                                          nerves, each serving a specific region    ceptors in the retina of the eye).        functions: sensory, integrative and
                                          on the right or left side of the body.      The branch of medical science          motor.
                                          A nerve is a bundle of hundreds to       that deals with the normal function-
mtj/massage therapy journal summer 2011

                                          thousands of axons, plus associated      ing and disorders of the nervous          Sensory function. The sensory recep-
                                          connective tissue and blood vessels      system is neurology. A neurologist is     tors detect many different types of
                                          that lie outside the brain and spinal    a physician who specializes in the        stimuli, both within your body, such
                                          cord. Nerves follow a defined path        diagnosis and treatment of disorders      as an increase in blood temperature,
                                          and serve specific regions of the body.   of the nervous system.                    and outside your body, such as a
                                          Ganglia (swelling or knot; singular is                                             touch on your arm. Sensory or affer-
                                          ganglion) contain cell bodies of neu-    FUNCTIONS OF THE                          ent neurons carry this sensory infor-
                                          rons, are located outside the brain      NERVOUS SYSTEM                            mation into the brain and spinal cord
                                          and spinal cord, and are closely asso-   Individual neurons carry incoming         through cranial and spinal nerves.
                                          ciated with cranial and spinal nerves.   signals, or communicate with an ar-
                                            The walls of organs of the gastro-     ray of neurons, or carry signals to ef-   Integrative function. The nervous
                                          intestinal tract contain extensive       fectors that produce an action. The       system integrates (processes) sen-
                                          networks of neurons—called enteric

                                                                                   nervous system thus carries out a         sory information by analyzing and
storing some of it and making de-        sensory information, as well as be-       sympathetic and parasympathetic.
cisions for appropriate responses.       ing the source of thoughts, emotions      With a few exceptions, effectors are
An important integrative function        and memories. Most nerve impulses         innervated by both divisions, and
is perception, the conscious aware-      that stimulate muscles to contract        the two divisions usually have op-
ness of sensory stimuli. Perception      and glands to secrete originate in        posing actions. For example, sympa-
occurs in the brain. Many of the         the CNS. Structural components of         thetic neurons speed the heartbeat,
neurons that participate in integra-     the PNS are cranial nerves and their      and parasympathetic neurons slow
tion are interneurons (association       branches, spinal nerves and their         it down. In general, the sympathetic
neurons), whose axons extend for         branches, ganglia and sensory recep-      division helps support exercise and/
only a short distance and contact        tors. The PNS is further subdivided       or emergency actions, so-called
nearby neurons in the brain or spi-      into a somatic nervous system (SNS),      fight-or-flight responses, and the
nal cord. Interneurons comprise the      an autonomic nervous system (ANS),        parasympathetic division takes care
vast majority of neurons in the body.    and an enteric nervous system (ENS).      of “rest and digest” activities.
                                            The somatic nervous system                The enteric system is the brain of
Motor function. Once a sensory           consists of 1) sensory neurons that       the gut, and its operation is involun-
stimulus is received, the nervous        convey information from somatic           tary. Its neurons extend most of the
system may elicit an appropriate         receptors in the head, body wall,         length of the gastrointestinal (GI)
motor response, such as muscular         viscera, and limbs and from recep-        tract. Sensory neurons of the enter-
contraction or glandular secretion.      tors for the special senses of vision,    ic nervous system monitor chemical
The neurons that serve this function     hearing, taste, and smell to the CNS,     changes within the GI tract and the
are motor (efferent) neurons. Motor      and 2) motor neurons that conduct         stretching of its walls. Enteric mo-
neurons carry information from the       impulses from the CNS to skeletal         tor neurons govern contraction of
brain toward the spinal cord, or out     muscles only. Because these motor         GI tract smooth muscle, secretions
of the brain and spinal cord to effec-   responses can be consciously con-         of the GI tract organs, such as acid
tors (muscles and glands) through        trolled, the action of this part of the   secretion by the stomach, and activ-
cranial and spinal nerves. Stimula-      PNS is voluntary.                         ity of GI tract endocrine cells.
tion of the effectors by motor neu-         The ANS consists of motor neu-
rons causes muscles to contract and      rons that conduct nerve impulses          PHYSIOLOGICAL EFFECTS OF
glands to secrete.                       from the CNS to smooth muscle,            APPROPRIATE MASSAGE ON
                                         cardiac muscle, and glands. Be-           NERVOUS TISSUE
ORGANIZATION OF THE                      cause its motor responses are not         Specific massage techniques are not
NERVOUS SYSTEM                           normally under conscious control,         the focus of this course, but most
The CNS integrates and correlates        the action of the ANS is involuntary.     comments apply to all nervous tis-
many different kinds of incoming            The ANS consists of two divisions,     sue. The following description is not

                                                                                                       THE TWO MAIN
                                                                                                       OF THE

                                                                                                       SYSTEM ARE
                                                                                                       THE CENTRAL
                                                                                                       AND THE
                                          complete, but includes many of the      large number of internal organs.       powers of regeneration, or the ca-
                                          widely accepted physiological ef-       * Massage increases the production     pability to replicate or repair them-
                                          fects of appropriate massage on ner-    and release of a number of neu-        selves. In the PNS, damage to den-
                                          vous tissue:                            rotransmitters and other substances    drites and myelinated axons may
                                          * Depending on the techniques uti-      from nervous tissue that facilitate    be repaired if the cell body remains
                                          lized, massage can be either stimu-     homeostasis.                           intact, and if the Schwann cells that
                                          lative or sedative to nervous tissue,                                          produce myelination remain ac-
                                          as well as other tissues associated     REGENERATION AND REPAIR OF NER-        tive. In the CNS, little or no repair
                                          with it, like muscles, for example.     VOUS TISSUE                            of damage to neurons occurs. Even
                                          *Massage releases or reduces emo-       Throughout your life, your nervous     when the cell body remains intact, a
                                          tional stress.                          system is capable of changing based    severed axon in the CNS cannot be
                                          * General massage tends to quiet        on experienced—called plasticity.      repaired or regrown.
                                          the sympathetic division of the auto-   At the level of individual neurons,
                                          nomic nervous system, that portion      the changes that can occur include     NEUROGENESIS IN THE CNS
                                          of the nervous system that responds     the sprouting of new dendrites, syn-   Neurogenesis—the birth of new
                                          to fight-or-flight situations.            thesis of new proteins and changes     neurons from undifferentiated stem
                                          * Massage enhances the develop-         in synaptic contacts with other        cells—occurs regularly in some ani-
                                          ment and growth of nervous tissue,      neurons. Undoubtedly, both chemi-      mals. For example, new neurons
                                          especially in newborn children.         cal and electrical signals drive the   appear and disappear every year in
                                          * Massage affects exteroceptors,        changes that occur.                    some songbirds.
                                          interoceptors, and proprioceptors         Despite plasticity, however, mam-       Until relatively recently, the dog-
                                          which, through reflexes, affect a        malian neurons have very limited       ma in humans and other primates
                                                                                                                         was “no new neurons” in the adult
                                                                                                                         brain. Then, in 1992, Canadian re-
                                                                                                                         searchers published their unexpect-
                                                                                                                         ed finding that epidermal growth
                                                                                                                         factor (EGF) stimulated cells taken
                                                                                                                         from the brains of adult mice to pro-
                                                                                                                         liferate into both neurons and astro-
                                                                                                                         cytes. Previously, EGF was known
                                                                                                                         to trigger mitosis in a variety of
                                                                                                                         non-neuronal cells, and to promote
                                                                                                                         wound healing and tissue regenera-
                                                                                                                         tion. In 1998, scientists discovered
                                                                                                                         that significant numbers of new
                                                                                                                         neurons do arise in the adult human
                                                                                                                         hippocampus, an area of the brain
                                                                                                                         that is crucial for learning.
mtj/massage therapy journal summer 2011

                                                                                                                         The nearly complete lack of neuro-
                                          MYELINATED                                                                     genesis in other regions of the brain
                                          AXONS IN THE                                                                   and spinal cord seems to result
                                          PERIPHERAL                                                                     from two factors: inhibitory influ-
                                          NERVOUS                                                                        ences from neuroglia—particularly
                                          SYSTEM MAY                                                                     oligodendrocytes—and absence of
                                          BE REPAIRED                                                                    growth-stimulating cues that were
                                          IF THE CELL                                                                    present during fetal development.
                                          BODY REMAINS                                                                   Axons in the CNS are myelinated by
                                          INTACT AND                                                                     oligodendrocytes that do not form
                                          IF SCHWANN                                                                     neurolemmas (sheaths of Schwann).
                                          CELLS REMAIN                                                                   In addition, CNS myelin is one of the

                                          ACTIVE.                                                                        factors inhibiting regeneration of
neurons. Perhaps this same mecha-
nism stops axonal growth once a tar-
get region has been reached during
development.                             A person who experiences neurapraxia or
   Also, after axonal damage, nearby
astrocytes proliferate rapidly, form-    axonotmesis of a nerve in an upper limb has
ing a type of scar tissue that acts as   a good chance of regaining nerve function.
a physical barrier to regeneration.
Thus, injury of the brain or spinal
cord usually is permanent. Ongoing          A person who experiences neura-        gap at the site of injury is too large,
research seeks ways to improve the       praxia or axonotmesis of a nerve          or if the gap becomes filled with col-
environment for existing spinal cord     in an upper limb, for example, has        lagen fibers.
axons to bridge the injury gap. Sci-     a good chance of regaining nerve            During the first few days following
entists also are trying to find ways to   function. When there is damage to         damage, buds of regenerating axons
stimulate dormant stem cells to re-      an axon, changes usually occur both       begin to invade the tube formed by
place neurons lost through damage        in the cell body of the affected neu-     the Schwann cells. Axons from the
or disease, and to develop tissue-cul-   ron and in the portion of the axon        proximal area grow at a rate of about
tured neurons that can be used for       distal to the site of injury. Changes     1.5 mm (0.06 in.) per day across the
transplantation purposes.                may also occur in the portion of the      area of damage, find their way into
                                         axon proximal to the site of injury.      the distal regeneration tubes, and
DAMAGE AND REPAIR IN THE PNS                About 24 to 48 hours after injury      grow toward the distally located re-
Axons and dendrites that are as-         to a process of a normal peripheral       ceptors and effectors. Thus, some
sociated with a neurolemma may           neuron, the Nissl bodies break up         sensory and motor connections are
undergo repair if 1) the cell body is    into fine granular masses. This alter-     reestablished and some functions
intact, 2) the Schwann cells (neuro-     ation is called chromatolysis. By the     restored. In time, the Schwann cells
lemmocytes) are functional, and 3)       third to fifth day, the part of the axon   form a new myelin sheath.
scar tissue formation does not occur     distal to the damaged region be-
too rapidly. Most nerves in the PNS      comes slightly swollen and breaks up      REPAIR OF DAMAGED NERVES
consist of processes that are covered    into fragments. The myelin sheath         Some neurons travel from the low-
with a neurolemma.                       also deteriorates. Even though the        er spinal cord to the great toe. The
   As occurs with most other sys-        axon and myelin sheath degenerate,        overall growth rate of 1.5 mm per
tems in the body, varying degrees        the neurolemma remains. Degenera-         day is approximately 2 inches per
of damage may occur in a nerve of        tion of the distal portion of the axon    month. Assuming that trauma of
the PNS. The mildest form of dam-        and myelin sheath is called Wallerian     a patient occurred in a peripheral
age that produces clinical deficits is    degeneration.                             nerve, but near the spinal cord, it
called neurapraxia, meaning there           Following chromatolysis, signs of      could take more than two years for
is a loss of nerve conduction, but the   recovery in the cell body become          the repair of damaged nerves, as evi-
axon does not degenerate and recov-      evident. Macrophages phagocytize          denced by the return of sensation
ery is complete.                         the debris. Synthesis of RNA and          and function of the great toe.
   More severe damage results in         protein accelerates, which favors            In another scenario, if a nerve (a
degeneration of the axon distal to       rebuilding or regeneration of the         bundle of neurons, some of which
the site of the lesion and is called     axon. The Schwann cells on either         are sensory and others motor) is
axonotmesis. In this instance, the       side of the injured site multiply by      completely severed, elastic fibers

connective tissue coverings are left     mitosis, grow toward each other,          around the nerve cause the two ends
intact and Wallerian degeneration of     and may form a regeneration tube          to be retracted. When this occurs,
axons occurs. The most severe dam-       across the injured area. This tube        the two ends must be connected
age to a nerve, wherein the associat-    guides growth of a new axon from          surgically. Although a surgeon will
ed connective tissues are also dam-      the proximal area across the injured      attempt to align the two cut ends by
aged, is called neurotmesis. With        area into the distal area previously      aligning the blood vessels that are
this condition, recovery of nerve        occupied by the original axon. How-       servicing the outside of the nerve,
function is highly unlikely.             ever, new axons cannot grow if the        it’s rare that the alignment of neu-
                                          rons is exactly correct.                 responses, such as pulling the foot      adult spinal cord ranges from 42–45
                                            As long as the nerve cell bodies       away quickly when we step on a           cm (16–18 in.). Its diameter is about
                                          are intact and scar tissue does not      sharp tack. We lift our foot before      2 cm (0.75 in.) in the mid-thoracic
                                          block the process, the neurons will      we have a chance to think.               region, somewhat larger in the lower
                                          regenerate and axonal growth into           This action is an example of a spi-   cervical and mid-lumbar regions,
                                          neurolemmal tunnels (regeneration        nal cord reflex—a quick, automatic        and smallest at the inferior tip.
                                          tubes) will take place. The axons        response to certain kinds of stimuli        When the spinal cord is viewed
                                          may, however, grow through differ-       that involves neurons only in the        externally, two conspicuous enlarge-
                                          ent tunnels. Assuming that regen-        spinal nerves and spinal cord. Re-       ments can be seen. The superior en-
                                          eration is complete, the brain may       flexes are simply preprogrammed           largement, the cervical enlargement,
                                          send messages down the “wrong”           reactions to strong stimuli such as      extends from the fourth cervical ver-
                                          motor neurons, and therefore the         pain, touch, temperature or pres-        tebra (C4) to the first thoracic ver-
                                          actions of the person may be inap-       sure. An example is when a physi-        tebra (T1). Nerves to and from the
                                          propriate.                               cian strikes near your elbow with a      upper limbs arise from the cervical
                                            Similarly, sensory neurons grow-       reflex hammer and an extensor re-         enlargement. The inferior enlarge-
                                          ing through different neurolemmal        flex pathway causes your upper limb       ment, called the lumbar enlarge-
                                          tunnels will result in inaccurate        to straighten.                           ment, extends from the ninth to the
                                          perceptions in the brain. Physical          The spinal cord is continuous         12th thoracic vertebra (T9–T12).
                                          therapy and other modalities may         with the medulla oblongata of the        Nerves to and from the lower limbs
                                          be required to retrain the brain so      brain. Both portions of the CNS con-     arise from the lumbar enlargement.
                                          that the appropriate actions and         tain gray and white matter for spe-         Inferior to the lumbar enlarge-
                                          perceptions will occur. As described     cialized processing of information.      ment, the spinal cord terminates as
                                          previously, manual therapy can be        Two types of connective tissue cov-      a tapering, conical structure called
                                          of value to the patient by maximiz-      erings—bony vertebrae and tough,         the conus medullaris, which ends at
                                          ing the flow of nutrients into the ar-    connective tissue meninges, plus a       the level of the intervertebral disc
                                          eas of healing (regeneration).           cushion of cerebrospinal fluid (pro-      between the first and second lumbar
                                                                                   duced in the brain)—surround and         vertebrae in adults. Arising from the
                                          The Spinal Cord and Spinal Nerves        protect the delicate nervous tissue      conus medullaris is the filum termi-
                                          Early anatomists made a distinction      of the spinal cord.                      nale (terminal filament), an exten-
                                          between the brain and spinal cord.                                                sion of the pia mater that extends
                                          Today we know that the brain and         External Anatomy of the Spinal Cord      inferiorly and anchors the spinal
                                          spinal cord are really just one large,   The spinal cord, although roughly        cord to the coccyx.
                                          interconnected group of nervous tis-     cylindrical, is flattened slightly in        Because the spinal cord is shorter
                                          sues known as the central nervous        its anterior–posterior dimension. In     than the vertebral column, nerves
                                          system (CNS). Since the nervous          adults, it extends from the medulla      that arise from the lumbar, sacral
                                          system is so complex, it’s more con-     oblongata, the inferior part of the      and coccygeal regions of the spi-
                                          venient to study the individual parts    brain, to the inferior border of the     nal cord do not leave the vertebral
                                          rather than the whole.                   first lumbar vertebra (L1) or the su-     column at the same level they exit
mtj/massage therapy journal summer 2011

                                            However, it is important to think      perior border of the second lumbar       the cord. The roots of these spinal
                                          of the nervous system as one com-        vertebra (L2). In newborn infants,       nerves angle inferiorly in the verte-
                                          plex mass of interconnected neu-         the spinal cord extends to the third     bral cavity from the end of the spi-
                                          rons. Function or dysfunction of any     or fourth lumbar vertebra.               nal cord like wisps of hair. Appro-
                                          part may affect many seemingly in-          During early childhood, both the      priately, the roots of these nerves
                                          dependent neuronal structures.           spinal cord and the vertebral column     are collectively named the cauda
                                            The spinal cord contains a series      grow longer as part of overall body      equina, meaning “horse’s tail.”
                                          of “pathways” that relay sensory         growth. Elongation of the spinal cord
                                          information along fibers to the pro-      stops around age 4 or 5, but growth      Internal Anatomy of the Spinal Cord
                                          cessing centers and then react by        of the vertebral column continues.       Two grooves penetrate the white
                                          sending information along different      Thus, the spinal cord does not ex-       matter of the spinal cord and divide
                                          fibers for motor function. The spi-       tend the entire length of the adult      it into right and left sides. The an-
                                                                                                                            terior median fissure is a deep, wide

                                          nal cord allows us to make quick         vertebral column. The length of the
                                                                                  SHOWING THE
                                                                                  COVERING OF A
                                                                                  SPINAL NERVE.

groove on the anterior (ventral)         sides of the spinal cord.                matter, is organized into regions.
side. The posterior median sulcus is a      In the gray matter of the spinal      The anterior and posterior gray
shallower, narrow groove on the pos-     cord and brain, clusters of neuronal     horns divide the white matter on
terior (dorsal) side. The gray matter    cell bodies form functional groups       each side into three broad areas
of the spinal cord is shaped like the    called nuclei. Sensory nuclei receive    called columns: (1) anterior (ven-
letter H or a butterfly and is sur-       input from sensory receptors via         tral) white columns, (2) posterior
rounded by white matter. The gray        sensory neurons, and motor nuclei        (dorsal) white columns, and (3) lat-
matter consists of dendrites and cell    provide output to effector tissues via   eral white columns. Each column,
bodies of neurons, unmyelinated ax-      motor neurons.                           in turn, contains distinct bundles
ons and neuroglia. The white matter         The gray matter on each side of       of axons having a common origin or
consists primarily of bundles of my-     the spinal cord is subdivided into       destination and carrying similar in-
elinated axons of neurons.               regions called horns. The anterior       formation.
                                         (ventral) gray horns contain somatic        These bundles, which may extend
The gray commissure forms the            motor nuclei, which provide nerve        long distances up or down the spi-
crossbar of the H. In the center of      impulses for contraction of skeletal     nal cord, are called tracts. Tracts
the gray commissure is a small space     muscles. The posterior (dorsal) gray     are bundles of axons in the CNS
called the central canal that extends    horns contain somatic and auto-          (you’ll recall that nerves are bundles
the entire length of the spinal cord     nomic sensory nuclei. Between the        of axons in the PNS). Sensory (as-
and is filled with cerebrospinal fluid.    anterior and posterior gray horns        cending) tracts consist of axons that

At its superior end, the central canal   are the lateral gray horns, which are    conduct nerve impulses toward the
is continuous with the fourth ventri-    present only in the thoracic, upper      brain. Tracts consisting of axons
cle (a space that contains cerebro-      lumbar and sacral segments of the        that carry nerve impulses from the
spinal fluid) in the medulla oblonga-     spinal cord. The lateral horns con-      brain are called motor (descending)
ta of the brain. Anterior to the gray    tain autonomic motor nuclei that         tracts. Sensory and motor tracts of
commissure is the anterior (ventral)     regulate the activity of smooth mus-     the spinal cord are continuous with
white commissure, which connects         cle, cardiac muscle and glands.          sensory and motor tracts in the
the white matter of the right and left      The white matter, like the gray       brain.
                                                                                                                          tween the spinal cord and the
                                                                                                                          nerves supplying specific regions of
                                          Motor output from the spinal cord to                                            the body. Spinal cord organization
                                          skeletal muscles involves somatic                                               appears to be segmented because
                                                                                                                          the 31 pairs of spinal nerves emerge
                                          motor neurons of the ventral gray                                               at regular intervals from interverte-
                                          horn. Many somatic motor neurons are                                            bral foramina.
                                                                                                                             Indeed, each pair of spinal nerves
                                          regulated by the brain.                                                         is said to arise from a spinal seg-
                                                                                                                          ment. Within the spinal cord, there
                                              The internal organization of the    brain into the white matter of the      is no obvious segmentation. But, for
                                           spinal cord allows sensory input and   spinal cord. There, they synapse        convenience, the naming of spinal
                                           motor output to be processed by the    with the somatic motor neurons          nerves is based on the segment in
                                           spinal cord in the following way:      either directly or indirectly by first   which they are located. There are
                                           Sensory receptors detect a sensory     synapsing with interneurons that        eight pairs of cervical nerves rep-
                                           stimulus.                              in turn synapse with somatic motor      resented as C1–C8, 12 pairs of tho-
                                                                                  neurons.                                racic nerves (T1–T12), five pairs of
                                           Sensory neurons convey this sensory                                            lumbar nerves (L1–L5), five pairs of
                                           input in the form of nerve impuls-     When activated, somatic motor neu-      sacral nerves (S1–S5) and one pair
                                           es along their axons, which extend     rons convey motor output in the form    of coccygeal nerves (Co1)—for a to-
                                           from sensory receptors into the spi-   of nerve impulses along their axons,    tal of 31 pairs.
                                           nal nerve and then into the dorsal     which sequentially pass through the        The first cervical pair emerges
                                           root. From the dorsal root, axons of   ventral gray horn and ventral root to   between the atlas (first cervical ver-
                                           sensory neurons may proceed along      enter the spinal nerve. From the spi-   tebra) and the occipital bone. All
                                           three possible paths.                  nal nerve, axons of somatic motor       other spinal nerves emerge from
                                                                                  neurons extend to skeletal muscles      the vertebral column through the
                                           Axons of sensory neurons may ex-       of the body.                            intervertebral foramina between
                                           tend into the white matter of the                                              adjoining vertebrae. Not all spinal
                                           spinal cord and ascend to the brain    Motor output from the spinal cord       cord segments are aligned with their
                                           as part of a sensory tract.            to cardiac muscle, smooth muscle,       corresponding vertebrae. Recall that
                                                                                  and glands involves autonomic mo-       the spinal cord ends near the level
                                           Axons of sensory neurons may enter     tor neurons of the lateral gray horn.   of the superior border of the second
                                           the dorsal gray horn and synapse       When activated, autonomic motor         lumbar vertebra, and that the roots
                                           with interneurons whose axons ex-      neurons convey motor output in          of the lumbar, sacral and coccygeal
                                           tend into the white matter of the      the form of nerve impulses along        nerves descend at an angle to reach
                                           spinal cord and then ascend to the     their axons, which sequentially pass    their respective foramina before
                                           brain as part of a sensory tract.      through the lateral gray horn, ven-     emerging from the vertebral col-
                                                                                  tral gray horn and ventral root to      umn. This arrangement constitutes
mtj/massage therapy journal summer 2011

                                           Axons of sensory neurons may enter     enter the spinal nerve.                 the cauda equina.
                                           the dorsal gray horn and synapse                                                  Two bundles of axons—called
                                           with interneurons that in turn syn-    From the spinal nerve, axons of auto-   roots—connect each spinal nerve to
                                           apse with somatic motor neurons        nomic motor neurons from the spinal     a segment of the cord by a series of
                                           that are involved in spinal reflex      cord synapse with another group of      small rootlets. The posterior (dorsal)
                                           pathways.                              autonomic motor neurons located in      root and rootlets contain only senso-
                                           Motor output from the spinal cord to   the PNS. The axons of this second       ry axons, which conduct nerve im-
                                           skeletal muscles involves somatic      group of autonomic motor neurons        pulses from sensory receptors in the
                                           motor neurons of the ventral gray      in turn synapse with cardiac mus-       skin, muscles and internal organs
                                           horn. Many somatic motor neurons       cle, smooth muscle and glands.          into the central nervous system.
                                           are regulated by the brain. Axons                                              Each posterior root has a swelling,
                                           from higher brain centers form mo-     Spinal nerves, part of the PNS, are     the posterior (dorsal) root ganglion,

                                           tor tracts that descend from the       the paths of communication be-          which contains the cell bodies of
sensory neurons. The anterior (ven-      ual therapy, pain medications and         The dura mater of the spinal me-
tral) root and rootlets contain axons    epidural injections are the most        ninges fuses with the epineurium as
of motor neurons, which conduct          widely used conservative treat-         the nerve passes through the inter-
nerve impulses from the CNS to ef-       ments. It is recommended that six       vertebral foramen. Note the pres-
fectors (muscles and glands). The        to 12 weeks of conservative therapy     ence of many blood vessels, which
dorsal and ventral roots unite to        be attempted first. If the pain con-     nourish nerves, within all three lay-
form a spinal nerve at the interver-     tinues, is intense, or is impairing     ers of connective tissue. The con-
tebral foramen. Because the dorsal       normal functioning, surgery is often    nective tissue coverings of skeletal
root contains sensory axons and the      the next step.                          muscles—endomysium, perimysi-
ventral root contains motor axons, a                                             um and epimysium—are similar in
spinal nerve is classified as a mixed     CONNECTIVE TISSUE COVERINGS OF          organization to those of nerves.
nerve.                                   SPINAL NERVES
                                         Each spinal nerve and cranial nerve     DISTRIBUTION OF SPINAL NERVES
Spinal Nerve Root Damage                 consists of many individual axons       Branches. A short distance after
As you have just learned, spinal         and contains layers of protective       passing through its intervertebral
nerve roots exit from the vertebral      connective tissue coverings. Indi-      foramen, a spinal nerve divides into
canal through intervertebral foram-      vidual axons within a nerve, wheth-     several branches. These branches
ina. The most common cause of            er myelinated or unmyelinated, are      are known as rami. The posterior
spinal nerve root damage is a herni-     wrapped in endoneurium the inner-       (dorsal) ramus (singular form)
ated intervertebral disc. Damage to      most layer. Groups of axons with        serves the deep muscles and skin of
vertebrae as a result of osteoporosis,   their endoneurium are arranged          the dorsal surface of the trunk. The
osteoarthritis, cancer or trauma can     in bundles called fascicles, each of    anterior (ventral) ramus serves the
also damage spinal nerve roots.          which is wrapped in perineurium,        muscles and structures of the upper
   Symptoms of spinal nerve root         the middle layer. The outermost         and lower limbs, as well as the skin
damage include pain, muscle weak-        covering over the entire nerve is the   of the lateral and ventral surfaces of
ness and loss of feeling. Rest, man-     epineurium.                             the trunk.


                                                                                                     SECTION OF
                                                                                                     SPINAL CORD.
                                                                               In addition to posterior and ante-    the accessory (XI) nerve and hypo-
                                                                            rior rami, spinal nerves also give off   glossal (XII) nerve.
                                                                            a meningeal branch. This branch re-        Complete transection of the spi-
                                                                            enters the vertebral cavity through      nal cord above the origin of the
                                                                            the intervertebral foramen, and sup-     phrenic nerves (C3, C4 and C5)
                                                                            plies the vertebrae, vertebral liga-     causes respiratory arrest. Breathing
                                                                            ments, blood vessels of the spinal       stops because the phrenic nerves no
                                                                            cord and meninges. Other branches        longer send nerve impulses to the
                                                                            of a spinal nerve are the rami com-      diaphragm.
                                                                            municantes, components of the au-
                                                                            tonomic nervous system.                  Intercostal Nerves. The anterior rami
                                                                                                                     of spinal nerves T2–T12 are not part
                                                                            Plexuses. Axons from the anterior        of the plexus and are known as in-
                                                                            rami of spinal nerves, except for        tercostal (thoracic) nerves. These
                                                                            thoracic nerves T2–T12, do not in-       nerves directly connect to the struc-
                                          INJURIES TO THE BRACHIAL PLEXUS   nervate the body structures directly.    tures they supply in the intercostal
                                          AFFECT THE SENSATIONS AND         Instead, they form networks on both      spaces. After leaving its interverte-
                                          MOVEMENTS OF THE UPPER LIMBS.     the left and right sides of the body     bral foramen, the anterior ramus of
                                                                            by joining with various numbers of       nerve T2 innervates the intercostal
                                                                            axons from anterior rami of adjacent     muscles of the second intercostal
                                                                            nerves. Such a network of axons is       space and supplies the skin of the
                                                                            called a plexus (the plural form may     axilla and posteromedial aspect of
                                                                            be plexuses or plexi).                   the arm.
                                                                              The principal plexuses are the cer-       Nerves T3–T6 extend along the
                                                                            vical, brachial, lumbar and sacral. A    costal grooves of the ribs and then
                                                                            smaller coccygeal plexus is also pres-   to the intercostal muscles and skin
                                                                            ent. Emerging from the plexuses are      of the anterior and lateral chest wall.
                                                                            nerves bearing names that are often      Nerves T7–T12 supply the intercos-
                                                                            descriptive of the general regions       tal muscles and abdominal muscles,
                                                                            they serve or the course they take.      and the overlying skin. The poste-
                                                                            Each of the nerves, in turn, may         rior rami of the intercostal nerves
                                                                            have several branches named for the      supply the deep back muscles and
                                                                            specific structures they innervate.       skin of the posterior aspect of the
                                                                            The anterior rami of spinal nerves       thorax.
                                                                            T2–T12 are called intercostal nerves.

                                                                            Cervical Plexus. The cervical plexus     Brachial Plexus. The roots (ventral
                                                                            is formed by the roots (ventral rami)    rami) of spinal nerves C5–C8 and
mtj/massage therapy journal summer 2011

                                                                            of the first four cervical nerves (C1–    T1 form the brachial plexus, which
                                                                            C4), with contributions from C5.         extends inferiorly and laterally on
                                                                            There is one on each side of the         either side of the last four cervical
                                                                            neck alongside the first four cervical    and first thoracic vertebrae, pass-
                                                                            vertebrae.                               ing between the anterior and middle
                                                                               The cervical plexus supplies the      scalene muscles and above the first
                                                                            skin and muscles of the head, neck,      rib posterior to the clavicle. The
                                                                            and superior part of the shoulders       plexus goes deep to the pectoralis
                                                                            and chest. The phrenic nerve arises      minor muscle and then enters the
                                               ERB-DUCHENNE PALSY           from the cervical plexus and sup-        axilla.
                                               (WAITER’S TIP)               plies motor fibers to the diaphragm.         Since the brachial plexus is so
                                                                            Branches of the cervical plexus also     complex, an explanation of its vari-

                                                                            run parallel to two cranial nerves,      ous parts is helpful. As with the cer-
vical and other plexuses, the roots      of the forearm and most of the mus-     excessive stretching of an infant’s
are the ventral rami of the spinal       cles of the hand.                       neck during childbirth.
nerves. The roots of several spinal                                                 The presentation of this injury
nerves unite to form trunks in the       Thoracic Outlet Syndrome                is characterized by an upper limb
inferior part of the neck. These are     Compression of the brachial plex-       where the shoulder is adducted, the
the superior, middle, and inferior       us on one or more of its nerves is      arm is medially rotated, the elbow is
trunks.                                  sometimes known as thoracic outlet      extended, the forearm is pronated
  Posterior to the clavicles, the        syndrome. The subclavian artery         and the wrist is flexed. This condi-
trunks divide into divisions, called     and subclavian vein may also be         tion is called Erb-Duchenne palsy
the anterior and posterior divisions.    compressed. The compression may         or waiter’s tip position. There is loss
In the axillae, the divisions unite to   result from spasm of the scalene or     of sensation along the lateral side of
form cords called the lateral, medial,   pectoralis minor muscles, the pres-     the arm.
and posterior cords. The cords are       ence of a cervical rib (an embryo-
named for their relationship to the      logical anomaly), or misaligned ribs.   Radial (and axillary) nerve injury can
axillary artery, a large artery that        The patient may experience pain,     be caused by improperly adminis-
supplies blood to the upper limb.        numbness, weakness or tingling in       tered intramuscular injections into
  The principal nerves of the bra-       the upper limb, across the upper        the deltoid muscle. The radial nerve
chial plexus branch from the cords.      thoracic area and over the scapula      may also be injured when a cast is
The brachial plexus provides the         on the affected side. The symp-         applied too tightly around the mid-
entire nerve supply of the shoul-        toms of thoracic outlet syndrome        humerus.
ders and upper limbs. Five impor-        are exaggerated during physical or        Radial nerve injury is indicated by
tant nerves arise from the brachial      emotional stress because the added      wrist drop, as well as the inability to
plexus: 1) axillary supplies the         stress increases the contraction of     extend the wrist and fingers. Senso-
deltoid and teres minor muscles,         the involved muscles.                   ry loss is minimal due to the overlap
2) musculocutaneous supplies the                                                 of sensory innervation by adjacent
flexors of the arm, 3) radial supplies    INJURIES TO NERVES EMERGING             nerves.
the muscles on the posterior aspect      FROM THE BRACHIAL PLEXUS
of the arm and forearm, 4) median        Injury to the roots of the brachial     Median nerve injury may result in
supplies most of the muscles of the      plexus (C5–C6) may result from          median nerve palsy, which is indi-
anterior forearm and some of the         forceful pulling away of the head       cated by numbness, tingling, and
muscles of the hand, and 5) ulnar        from the shoulder, as might occur       pain in the palm and fingers. There
supplies the anteromedial muscles        from a heavy fall on the shoulder or    is also an inability to pronate the

                                                                                 INJURIES TO
                                                                                 THE BRACHIAL
                                                                                 AFFECT THE

                                                                                 OF THE UPPER
               WRIST DROP                       MEDIAN NERVE PALSY               LIMBS.
                                          forearm and flex the proximal in-          numbness, tingling, or pain of the      can also be caused by compression
                                          terphalangeal joints of all digits, and   wrist and hand. Compression with-       of the median nerve in two areas of
                                          the distal interphalangeal joints of      in the tunnel usually results from      the shoulder. When this occurs, car-
                                          the second and third digits.              inflamed and thickened tendon            pal tunnel surgery will not alleviate
                                            In addition, wrist flexion and           sheaths of flexor tendons, fluid re-      the pain. Furthermore, scar tissue
                                          thumb movements are weak, and             tention, excessive exercise, infec-     formed after the surgery may exac-
                                          are accompanied by adduction of           tion, trauma, and/or repetitive ac-     erbate the problem.
                                          the thumb due to a loss of function       tivities that involve flexion of the        Compression of the median nerve
                                          of the muscles of the thenar emi-         wrist such as keyboarding, cutting      can also occur between the anterior
                                          nence.                                    hair and playing a piano.               and middle scalenes or deep to the
                                                                                       Treatment may be progressive if      pectoralis minor. Pain in the wrist or
                                          Carpal tunnel pain is caused by com-      the problem worsens. Initial treat-     hand is perceived by the patient and
                                          pression of the median nerve. The         ment may include aspirin or ibu-        is identical to the pain of true car-
                                          carpal tunnel is a narrow passage-        profen (both are anti-inflammatory       pal tunnel syndrome. Massage of the
                                          way formed anteriorly by the flexor        drugs), and may progress to an in-      scalenes and pectoralis minor can
                                          retinaculum and posteriorly by the        jection of cortisone into the carpal    usually lengthen those muscles, and
                                          carpal bones. Through this tunnel         tunnel. Persons might be asked to       thereby reduce impingement on the
                                          pass the median nerve, the most su-       keep the wrist straight to minimize     median nerve. By lengthening these
                                          perficial structure, and the long flex-     movement of the inflamed tendon          muscles, a manual therapist can
                                          or tendons for the digits. Structures     sheaths, and some type of splint or     usually determine within minutes
                                          within the carpal tunnel, especially      brace may be prescribed.                whether the pain of the wrist and
                                          the median nerve, are vulnerable             Continued pain may necessitate       hand may be a function of compres-
                                          to compression, and the resulting         surgery to cut (release) the trans-     sion of the median nerve in the neck
                                          condition is known as carpal tunnel       verse carpal ligament and relieve the   or axilla, or compression of the me-
                                          syndrome.                                 compression of the nerve. It should     dian nerve within the carpal tunnel.
                                            The person may experience               be noted that “carpal tunnel pain”
                                                                                                                            Ulnar nerve injury may result in ul-
                                                                                                                            nar nerve palsy (claw hand), which
                                                                                                                            is indicated by an inability to abduct
                                                                                                                            or adduct the fingers, atrophy of the
                                                                                                                            interosseus muscles of the hand,
                                                                                                                            hyperextension of the metacarpo-
                                                                                                                            phalangeal joints, and flexion of the
                                                                                                                            interphalangeal joints—a condition
                                                                                                                            called claw hand. People with the
                                                                                                                            condition might also experience a
                                                                                                                            loss of sensation over the little finger
                                                                                                                            and the medial half of the ring finger.
mtj/massage therapy journal summer 2011

                                                                                                                            Long thoracic nerve injury results in
                                                                                                                            paralysis of the serratus anterior
                                                                                                                            muscle. The medial border of the
                                                                                                                            scapula protrudes, giving it the ap-
                                                                                                                            pearance of a wing. When the arm is
                                                                                                                            raised, the vertebral border and in-
                                                                                                                            ferior angle of the scapula pull away
                                                                                                                            from the thoracic wall and protrude
                                                                                                                            outward, causing the medial border
                                                                                                                            of the scapula to protrude. Because
                                          THE LUMBAR PLEXUS SUPPLIES THE ANTEROLATERAL ABDOMINAL WALL,                      the scapula looks like a wing, this

                                          EXTERNAL GENITALS AND PART OF THE LOWER LIMBS.                                    condition is called winged scapula.
The arm cannot be abducted be-           ges, however, extend to the second
yond the horizontal position.            sacral vertebra (S2).
                                            Between vertebrae L2 and S2, the
Lumbar Plexus. The roots (ventral        spinal meninges are present—but
rami) of spinal nerves L1–L4 form        the spinal cord is absent. Conse-
the lumbar plexus. Unlike the bra-       quently, a spinal tap is normally per-
chial plexus, there is no intricate      formed in adults between vertebrae
intermingling of fibers in the lumbar     L3 and L4 or L4 and L5 because this
plexus. On either side of the first       region provides safe access to the
four lumbar vertebrae, the lumbar        subarachnoid space without the risk
plexus passes obliquely outward,         of damaging the spinal cord. (A line
posterior to the psoas major muscle      drawn across the highest points of
and anterior to the quadratus lum-       the iliac crests, called the supracris-
borum muscle. It then gives rise to      tal line, passes through the spinous
its peripheral nerves. The lumbar        process of the fourth lumbar verte-       A DERMATOME IS AN AREA OF SKIN
plexus supplies the anterolateral ab-    bra.)                                     THAT PROVIDES SENSORY INPUT TO
dominal wall, external genitals and         A spinal tap is used to withdraw       THE CENTRAL NERVOUS SYSTEM.
part of the lower limbs.                 cerebrospinal fluid (CSF) for diag-
                                         nostic purposes, as well as to in-
Sacral Plexus. The roots (ventral        troduce antibiotics, contrast media
rami) of spinal nerves L4–L5 and         for myelography, or anesthetics.
S1–S4 form the sacral plexus. This       Other uses include administering
plexus is situated largely anterior to   chemotherapy, measuring CSF pres-
the sacrum. The sacral plexus sup-       sure, and/or evaluating the effects of
plies the buttocks, perineum and         treatment for diseases such as men-
lower limbs. The largest nerve in        ingitis.
the body—the sciatic nerve—arises
from the sacral plexus.                  Dermatomes. The skin over the en-
                                         tire body is supplied by somatic sen-
Coccygeal Plexus. The roots (ventral     sory neurons that carry nerve im-
rami) of spinal nerves S4–S5 and         pulses from the skin into the spinal
the coccygeal nerves form a small        cord and brain. Each spinal nerve,
coccygeal plexus, which supplies a       except for C1, contains sensory neu-
small area of skin in the coccygeal      rons that serve a specific, predict-
region.                                  able segment of the body.
                                            One of the cranial nerves—the
Spinal Tap                               trigeminal (V) nerve—serves most
In a spinal tap (lumbar puncture), a     of the skin of the face and scalp. The
local anesthetic is given, and a long    area of the skin that provides sen-
needle is inserted into the subarach-    sory input to the CNS via one pair of
noid space. During this procedure,       spinal nerves or the trigeminal (V)
the patient lies on their side with      nerve is called a dermatome. The
the vertebral column flexed, like         nerve supply in adjacent derma-

when in the fetal position.              tomes overlaps somewhat.
  Flexion of the vertebral column           Knowing which spinal cord seg-
increases the distance between the       ments supply each dermatome
spinous processes of the vertebrae,      makes it possible to locate damaged
which allows easy access to the sub-     regions of the spinal cord. If the skin
arachnoid space. The spinal cord         in a particular region is stimulated
ends around the second lumbar            but the sensation is not perceived,
vertebra (L2). The spinal menin-         the nerves supplying that derma-
                                                                                                                              nerves—tibial and common fibu-
                                                                                                                              lar—bound together by a common
                                                                                                                              sheath of connective tissue. This
                                                                                                                              nerve splits into its two divisions,
                                                                                                                              usually at the knee.
                                                                                                                                 Sciatic nerve injury results in sci-
                                                                                                                              atica, pain that may extend from
                                                                                                                              the buttock down the posterior and
                                                                                                                              lateral aspect of the leg and the lat-
                                                                                                                              eral aspect of the foot. The sciatic
                                                                                                                              nerve may be injured because of a
                                                                                                                              herniated (slipped) disc, dislocated
                                                                                                                              hip, osteoarthritis of the lumbosa-
                                                                                                                              cral spine, pathological shortening
                                                                                                                              of the lateral rotator muscles of the
                                                                                                                              thigh (especially piriformis), pres-
                                                                                                                              sure from the uterus during preg-
                                                                                                                              nancy, inflammation, irritation or
                                                                                                                              an improperly administered gluteal
                                                                                                                              intramuscular injection. In addition,
                                          POSTERIOR                                                                           sitting on a wallet or other object for
                                          COLUMN-                                                                             a long period of time can also com-
                                          MEDIAL                                                                              press the nerve and induce pain.
                                          LEMNISCUS                                                                              In many sciatic nerve injuries, the
                                          PATHWAY.                                                                            common fibular portion is the most
                                                                                                                              affected, frequently from fractures
                                                                                                                              of the fibula or by pressure from
                                                                                                                              casts or splints over the thigh or
                                                                                                                              leg. Damage to the common fibular
                                          tome are probably damaged. In re-        rus retreats to a posterior root gan-      nerve causes the foot to be plantar
                                          gions where the overlap is consid-       glion. If the virus is reactivated, the    flexed, a condition called foot drop,
                                          erable, little loss of sensation may     immune system usually prevents it          and inverted, a condition called
                                          result if only one of the nerves sup-    from spreading.                            equinovarus.
                                          plying the dermatome is damaged.            From time to time, however, the            There is also loss of function along
                                             Information about the innerva-        reactivated virus overcomes a weak-        the anterolateral aspects of the leg
                                          tion patterns of spinal nerves can       ened immune system, leaves the             and dorsum of the foot and toes. In-
                                          also be used therapeutically. Cut-       ganglion, and travels down sensory         jury to the tibial portion of the sciat-
                                          ting posterior roots or infusing local   neurons of the skin by fast axonal         ic nerve results in dorsiflexion of the
mtj/massage therapy journal summer 2011

                                          anesthetics can block pain either        transport. The result is pain, discol-     foot plus eversion, a condition called
                                          permanently or transiently. Because      oration of the skin and a character-       calcaneovalgus. Loss of sensation on
                                          dermatomes overlap, deliberate           istic line of skin blisters. The line of   the sole also occurs. Treatments for
                                          production of a region of complete       blisters marks the distribution (der-      sciatica are similar to those outlined
                                          anesthesia may require that at least     matome) of the particular cutane-          earlier for a herniated (slipped)
                                          three adjacent spinal nerves be cut      ous sensory nerve belonging to the         disc—rest, pain medications, exer-
                                          or blocked by an anesthetic drug.        infected posterior root ganglion.          cises, ice or heat and massage. The
                                                                                                                              topics of nerve injuries and the ef-
                                          Shingles. This acute infection of the    Sciatic Nerve Injury. The most com-        fects on muscles cannot be well dif-
                                          peripheral nervous system is caused      mon form of back pain is caused            ferentiated.
                                          by herpes zoster, the virus that also    by compression or irritation of the           A very common cause of sci-
                                          causes chicken pox. After a person       sciatic nerve, the longest nerve in        atic pain is spasm of the piriformis

                                          recovers from chicken pox, the vi-       the human body. It is actually two         muscle. Remember that spasm of a
muscle causes the muscle belly to
shorten and to become thicker. The
sciatic nerve exits the bony sacrum
and usually lies deep to the pirifor-
                                          The spinal cord has two principal
mis. In a small percentage of the         functions in maintaining homeostasis:
population, the sciatic nerve actual-
ly pierces the belly of the piriformis.
                                          nerve impulse propagation and
   The level of compression of the        integration of information.
sciatic nerve by the piriformis is
highly variable, and the pain expe-       cord receives and integrates incom-      From the neck, trunk, limbs and
rienced is highly variable, as well.      ing and outgoing information.            posterior aspect of the head, somat-
The piriformis is a lateral rotator of                                             ic sensory impulses propagate along
the thigh. Overuse of the muscle can      SENSORY AND MOTOR TRACTS                 spinal nerves into the spinal cord.
occur with repetitive lateral rotation    One of the ways the spinal cord pro-
of the thigh (and subsequent lateral      motes homeostasis is by conducting       Second-order neurons conduct im-
movement of the foot), as you might       nerve impulses along tracts. Often,      pulses from the brain stem and spi-
see in dancing. The lateral rotators      the name of a tract indicates its po-    nal cord to the thalamus. Axons of
also can be overused by planting the      sition in the white matter, as well as   second-order neurons decussate
feet solidly on the floor and then ro-     where it begins and ends. For ex-        (cross over to the opposite side) in
tating the torso, as is seen in some      ample, the anterior spinothalamic        the brain stem or spinal cord before
assembly-line work.                       tract is located in the anterior white   ascending to the thalamus. Thus, all
   The piriformis is very deep, and       column, beginning in the spinal cord     somatic sensory information from
its location may be difficult for the      and ending in the thalamus (a region     one side of the body reaches the
beginning student to find. The piri-       of the brain). Notice that the loca-     thalamus on the opposite side.
formis is located along a line be-        tion of the axon terminals comes         Third-order neurons conduct impuls-
tween the middle of the sacrum            last in the name.                        es from the thalamus to the primary
and the greater trochanter. Access           This regularity in naming allows      somatosensory area of the cortex on
to this deep muscle is possible only      you to determine the direction of        the same side.
after softening the gluteal muscles.      information flow along any tract             Somatic sensory impulses ascend
Whereas most manual therapy treat-        named according to this convention.      to the cerebral cortex via two main
ments involve moving the therapist’s      Because the anterior spinothalamic       pathways: 1) the posterior column–
hands along the length of a muscle        tract conveys nerve impulses from        medial lemniscus pathway, and 2)
belly, in the case of the piriformis,     the spinal cord toward the brain, it’s   the anterolateral spinothalamic
the therapist can locate and then         a sensory (ascending) tract.             pathways.
deeply plant her thumb into the                                                       Nerve impulses for touch, pres-
piriformis. Passive movement of the       Somatic sensory pathways relay in-       sure, vibration and conscious pro-
patient’s flexed leg causes the belly      formation from the somatic sensory       prioception (awareness of the posi-
of the piriformis to slide beneath the    receptors to the primary somatosen-      tions of body parts) from the limbs,
stationary thumb of the therapist.        sory area in the cerebral cortex and     trunk, neck and posterior head as-
   The spinal cord has two principal      to the cerebellum. The pathways to       cend to the cerebral cortex along
functions in maintaining homeo-           the cerebral cortex consist of thou-     the posterior column–medial lem-
stasis: nerve impulse propagation         sands of sets of three neurons: a        niscus pathway. The name of the
and integration of information. The       first-order neuron, a second-order        pathway comes from the names of

white matter tracts in the spinal         neuron and a third-order neuron.         two white-matter tracts that convey
cord are highways for nerve impulse                                                the impulses: the posterior column
propagation. Sensory input travels        First-order neurons conduct impuls-      of the spinal cord and the medial
along these tracts toward the brain,      es from somatic receptors into the       lemniscus of the brain stem.
and motor output travels from the         brain stem or spinal cord. From the         Nerve impulses for pain, tempera-
brain along these tracts toward skel-     face, mouth, teeth and eyes, somatic     ture, itch and tickle from the limbs,
etal muscles and other effector tis-      sensory impulses propagate along         trunk, neck and posterior head as-
sues. The gray matter of the spinal       cranial nerves into the brain stem.      cend to the cerebral cortex along
                                          the anterolateral or spinothalamic      nerve impulses that originate in the     spastic movements. Application of
                                          pathway. This pathway begins in         cerebral cortex and are destined to      hot or cold lubricants, effleurage,
                                          two spinal cord tracts—the lateral      cause precise, voluntary movements       pettrisage and other techniques—as
                                          and anterior spinothalamic tracts.      of skeletal muscles.                     well as warm or cool temperature of
                                             The spinocerebellar tracts are the      Indirect motor pathways located       the room—are a few stimuli that will
                                          major routes that proprioceptive im-    in the spinal cord include the ru-       induce spastic movements. If you
                                          pulses take to reach the cerebellum.    brospinal, reticulospinal, tectospi-     are dressing the patient after treat-
                                          Although they are not consciously       nal, and vestibulospinal tracts. They    ment, tying the shoe laces too tight-
                                          perceived, sensory impulses con-        convey nerve impulses from the           ly is another example of a stimulus
                                          veyed to the cerebellum along these     brain stem and other parts of the        that will be problematic for the pa-
                                          pathways are critical for posture,      brain that govern automatic move-        tient with severe spasticity.
                                          balance and coordination of move-       ments and help coordinate body
                                          ments.                                  movements with visual stimuli. Indi-     Muscle Spindles. Muscle spindles
                                             The sensory systems keep the CNS     rect pathways also maintain skeletal     are the proprioceptors in skeletal
                                          informed of changes in the external     muscle tone, maintain contraction        muscles that monitor changes in
                                          and internal environments. The          of postural muscles, and play a ma-      the length of skeletal muscles and
                                          sensory information is integrated by    jor role in equilibrium by regulating    participate in stretch reflexes. By
                                          interneurons in the spinal cord and     muscle tone in response to move-         adjusting how vigorously a muscle
                                          brain. Responses to the integrative     ments of the head.                       spindle responds to stretching of a
                                          decisions (muscular contractions of                                              skeletal muscle, the brain sets an
                                          all three types of muscles and glan-    WORKING WITH PATIENTS                    overall level of muscle tone—the
                                          dular secretions) are brought about     WITH PARALYSIS                           small degree of contraction that is
                                          by motor activities.                    Damage or disease of lower motor         present while the muscle is at rest.
                                             Neurons in the brain and spinal      neurons produces flaccid paralysis        Each muscle spindle consists of sev-
                                          cord coordinate all voluntary and       of muscles on the same (ipsilateral)     eral slowly adapting sensory nerve
                                          involuntary movements. All somat-       side of the body: The muscles lack       endings that wrap around three to
                                          ic motor pathways involve at least      voluntary control and reflexes, mus-      10 specialized muscle fibers, called
                                          two motor neurons. The cell bodies      cle tone is decreased or lost, and the   intrafusal fibers. A connective tis-
                                          of upper motor neurons are in the       muscle remains flaccid (limp). In-        sue capsule encloses the sensory
                                          higher integration centers of the       jury or disease of upper motor neu-      nerve endings and intrafusal fibers,
                                          CNS. The axons of lower motor neu-      rons causes spastic paralysis of mus-    anchoring the spindle to the endo-
                                          rons extend out of the brain stem       cles on the opposite (contralateral)     mysium and perimysium.
                                          to stimulate skeletal muscles in the    side of the body. In this condition,        Muscle spindles are interspersed
                                          head, and out of the spinal cord to     muscle tone is increased, reflexes        among most skeletal muscle fibers
                                          stimulate skeletal muscles in the       are exaggerated and pathological re-     and aligned parallel to them. In
                                          limbs and trunk.                        flexes appear.                            muscles that produce finely con-
                                             The cerebral cortex—the outer           Manual therapists should be aware     trolled movements, such as those of
                                          part of the brain—plays a major         that patients with spinal cord injury    the fingers or eyes, muscle spindles
mtj/massage therapy journal summer 2011

                                          role in controlling precise volun-      confined to wheelchairs have vary-        are plentiful. Muscles involved in
                                          tary muscular movements. Other          ing degrees of spastic paralysis. Pa-    coarser but more forceful move-
                                          brain regions provide important in-     tients with moderate spasticity are      ments, like the quadriceps femo-
                                          tegration for regulation of automatic   usually prescribed medications that      ris and hamstring muscles of the
                                          movements, such as arm swinging         reduce the severity. Patients with       thigh, have fewer muscle spindles.
                                          during walking.                         severe spasticity commonly have          The only skeletal muscles that lack
                                             Motor output to skeletal muscles     their lower limbs strapped to the        spindles are the tiny muscles of the
                                          travels down the spinal cord in two     wheelchair so that the uncontrolled      middle ear.
                                          types of descending pathways: di-       movements of the limbs don’t cause          The main function of muscle
                                          rect and indirect. The direct motor     bruising, fracture or other trauma.      spindles is to measure muscle
                                          pathways in the spinal cord include        When a patient is on your table,      length—how much a muscle is be-
                                          the lateral corticospinal and anteri-   only the slightest environmental         ing stretched. Either sudden or

                                          or corticospinal tracts. They convey    stimulus may cause uncontrolled          prolonged stretching of the central
                                                                                                  ABOUT BODY
                                                                                                  POSITION AND

areas of the intrafusal muscle fibers    stimulate the ends of the intrafusal     muscle. In this way, activation of its
stimulates the sensory nerve end-       fibers to contract slightly. This keeps   muscle spindles causes contraction
ings. The resulting nerve impulses      the intrafusal fibers taut, and main-     of a skeletal muscle, which relieves
propagate into the CNS. Informa-        tains the sensitivity of the muscle      the stretching.
tion from muscle spindles arrives       spindle to stretching of the muscle.
quickly at the somatic sensory areas    As the frequency of impulses in its      Tendon Organs. Tendon organs are lo-
of the cerebral cortex, which allows    gamma motor neuron increases, a          cated at the junction of a tendon and
conscious perception of limb posi-      muscle spindle becomes more sensi-       a muscle. By initiating tendon reflex-
tions and movements. At the same        tive to stretching of its mid-region.    es, tendon organs protect tendons
time, impulses from muscle spindles        Surrounding muscle spindles           and their associated muscles from
pass to the cerebellum, where the       are ordinary skeletal muscle fibers,      damage due to excessive tension.
input is used to coordinate muscle      called extrafusal muscle fibers,             A contracting muscle exerts a
contractions.                           which are supplied by large-diameter     force that pulls the points of attach-
   In addition to their sensory nerve   A fibers called alpha motor neurons.      ment of the muscle at either end
endings near the middle of intrafusal   The cell bodies of both gamma and        toward each other. This force is the
fibers, muscle spindles contain mo-      alpha motor neurons are located in       muscle tension. Each tendon organ

tor neurons called gamma motor          the anterior gray horn of the spinal     consists of a thin capsule of connec-
neurons. These motor neurons ter-       cord (or in the brain stem for mus-      tive tissue that encloses a few ten-
minate near both ends of the intra-     cles in the head). During the stretch    don fascicles (bundles of collagen
fusal fibers and adjust the tension in   reflex, impulses in muscle spindle        fibers). Penetrating the capsule are
a muscle spindle to variations in the   sensory axons propagate into the spi-    one or more sensory nerve endings
length of the muscle organ.             nal cord and brain stem and activate     that entwine among and around
   For example, when a muscle           alpha motor neurons that connect to      the collagen fibers of the tendon.
shortens, gamma motor neurons           extrafusal muscle fibers in the same      When tension is applied to a muscle,
                                          OF A REFLEX

                                          the tendon organs generate nerve         which involve contraction of skel-
                                          impulses that propagate into the         etal muscles. Equally important,          2. Sensory neuron. The nerve im-
                                          CNS, providing information about         however, are the autonomic (viscer-       pulses propagate from the sensory
                                          changes in muscle tension. Tendon        al) reflexes, which generally are not      receptor along the axon of the sen-
                                          reflexes decrease muscle tension by       consciously perceived. They involve       sory neuron to the axon terminals,
                                          causing muscle relaxation.               responses of smooth muscle, car-          which are located in the gray matter
                                                                                   diac muscle and glands. Body func-        of the spinal cord or brain stem.
                                          Reflexes and Reflex Arcs. The sec-       tions—such as heart rate, digestion,
                                          ond way the spinal cord promotes         urination and defecation—are con-         3. Integrating center. One or more
                                          homeostasis is by serving as an in-      trolled by the autonomic nervous          regions of gray matter within the
                                          tegrating center for some reflexes.       system through autonomic reflexes.         CNS act as an integrating center.
                                          A reflex is a fast, automatic, un-           Nerve impulses propagating into,       In the simplest type of reflex, the
                                          planned sequence of actions that         through and out of the CNS follow         integrating center is a single syn-
                                          occurs in response to a particular       specific pathways, depending on the        apse between a sensory neuron and
                                          stimulus. Some reflexes are inborn,       kind of information, its origin and its   a motor neuron. A reflex pathway
                                          such as pulling your hand away           destination. The pathway followed         having only one synapse in the CNS
                                          from a hot surface before you even       by nerve impulses that produce a re-      is termed a monosynaptic reflex arc.
                                          feel that it is hot. Other reflexes are   flex is a reflex arc (reflex circuit). A     More often, the integrating center
                                          learned or acquired. For instance,       reflex arc includes the following five      consists of one or more interneu-
                                          you learn many reflexes while ac-         functional components:                    rons, which may relay impulses to
                                          quiring driving expertise. Slamming                                                other interneurons as well as to a
mtj/massage therapy journal summer 2011

                                          on the brakes in an emergency is         1. Sensory receptor. The distal end       motor neuron. A polysynaptic reflex
                                          one example.                             of a sensory neuron (dendrite) or an      arc involves more than two types
                                             When integration takes place in       associated sensory structure serves       of neurons and more than one CNS
                                          the spinal cord gray matter, the re-     as a sensory receptor. It responds        synapse.
                                          flex is a spinal reflex. An example        to a specific stimulus—a change in
                                          is the familiar patellar reflex (knee     the internal or external environ-         4. Motor neuron. Impulses triggered
                                          jerk). If integration occurs in the      ment—by producing a graded po-            by the integrating center propagate
                                          brain stem rather than the spinal        tential called a generator (or recep-     out of the CNS along a motor neu-
                                          cord, the reflex is called a cranial      tor) potential. If a generator poten-     ron to the part of the body that will
                                          reflex. An example is the track-          tial reaches the threshold level of       respond.
                                          ing movements of your eyes as you        depolarization, it will trigger one or
                                          read this sentence. You are prob-        more nerve impulses in the sensory        5. Effector. The part of the body

                                          ably most aware of somatic reflexes,      neuron.                                   that responds to the motor nerve
impulse, such as a muscle or gland,       son will have permanent loss of all       loss of reflex function. The areflexia
is the effector. Its action is called a   sensations in dermatomes below            occurs in parts of the body served by
reflex. If the effector is skeletal mus-   the injury because ascending nerve        spinal nerves below the level of the
cle, the reflex is a somatic reflex. If     impulses cannot propagate past the        injury. Signs of acute spinal shock
the effector is smooth muscle, car-       transection to reach the brain.           include slow heart rate, low blood
diac muscle or a gland, the reflex is         At the same time, voluntary mus-       pressure, flaccid paralysis of skeletal
an autonomic (visceral) reflex.            cle contractions will be lost below       muscles, loss of somatic sensations
                                          the transection because nerve im-         and urinary bladder dysfunction.
TRAUMATIC INJURIES OF THE                 pulses descending from the brain          Spinal shock may begin within one
SPINAL CORD                               also cannot pass. The extent of pa-       hour after injury, and may last from
Most spinal cord injuries are due to      ralysis of skeletal muscles depends       several minutes to several months,
trauma that results from incidents        on the level of injury.                   after which reflex activity gradually
such as automobile accidents, falls,         The following list outlines which      returns.
contact sports, diving or acts of vio-    muscle functions may be retained at          In many cases of traumatic injury
lence. The effects of the injury de-      progressively lower levels of spinal      of the spinal cord, the patient may
pend on the extent of direct trauma       cord transection.                         have an improved outcome if an an-
to the spinal cord or compression of      • C1–C3: No function maintained           ti-inflammatory corticosteroid drug
the cord by fractured or displaced           from the neck down; ventilator         called methylprednisolone is given
vertebrae or blood clots. Although           needed for breathing.                  within eight hours of the injury. This
any segment of the spinal cord may        • C4–C5: Diaphragm, which allows          is because the degree of neurological
be involved, most common sites of            breathing.                             deficit is greatest immediately fol-
injury are in the cervical, lower tho-    • C6–C7: Some arm and chest mus-          lowing traumatic injury as a result
racic and upper lumbar regions.              cles, which allows feeding, some       of edema (collection of fluid within
   Depending on the location and ex-         dressing and propelling wheel-         tissues) as the immune system re-
tent of spinal cord damage, paralysis        chair.                                 sponds to injury.
may occur. Monoplegia is paralysis        • T1–T3: Intact arm function.                Much of this article has been ab-
of one limb only, and diplegia is pa-     • T4–T9: Control of trunk above the       stracted from portions of Anatomy
ralysis of both upper limbs or both          umbilicus.                             and Physiology of the Manual Ther-
lower limbs. Paraplegia is paralysis      • T10–L1: Most thigh muscles,             apies by Andrew J. Kuntzman and
of both lower limbs, and hemiplegia          which allows walking with long leg     Gerard J. Tortora, 2010, John Wiley
is paralysis of the upper limb, trunk        braces.                                & Sons, Inc.                         ■

and lower limb on one side of the         • L1–L2: Most leg muscles, which                           Andrew J.
body. Quadriplegia is paralysis of all       allows walking with short leg brac-                     Kuntzman,
four limbs.                                  es.                                                     Ph.D., LMT,
                                          Hemisection is a partial transection                       teaches anatomy
Complete transection of the spinal        of the cord on either the right or left                    and physiology
cord means that the cord is severed       side. Following complete transec-                          at Sinclair
from one side to the other, thus cut-     tion, and to varying degrees after                         Community
ting all sensory and motor tracts—        hemisection, spinal shock occurs.                          College in Dayton,
resulting in a loss of all sensations     Spinal shock is an immediate re-          Ohio. He also has taught massage
and voluntary movement below              sponse to spinal cord injury char-        and massage theory over the past
the level of the transection. A per-      acterized by temporary areflexia, or       17 years.

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