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MASSAGE & THE SPINAL CORD AND SPINAL NERVES ANDREW J. KUNTZMAN, PH.D., LMT COURSE DESCRIPTION: COURSE OBJECTIVES: 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. www.amtamassage.org/mtj 65 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 66 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 SUBDIVISIONS OF THE NERVOUS www.amtamassage.org/mtj 67 SYSTEM ARE THE CENTRAL NERVOUS SYSTEM AND THE PERIPHERAL NERVOUS SYSTEM. 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 68 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 www.amtamassage.org/mtj 69 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 70 nal cord allows us to make quick vertebral column. The length of the TRANSVERSE SECTION 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 www.amtamassage.org/mtj 71 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, 72 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. www.amtamassage.org/mtj 73 TRANSVERSE SECTION OF THORACIC 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- 74 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 PLEXUS AFFECT THE SENSATIONS www.amtamassage.org/mtj 75 AND MOVEMENTS 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 76 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- www.amtamassage.org/mtj 77 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 78 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 www.amtamassage.org/mtj 79 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 80 or corticospinal tracts. They convey stimulus may cause uncontrolled prolonged stretching of the central PROPRIOCEPTORS PROVIDE INFORMATION ABOUT BODY POSITION AND MOVEMENT. 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 www.amtamassage.org/mtj 81 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, GENERAL COMPONENTS OF A REFLEX ARC. 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 82 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. www.amtamassage.org/mtj 83 This mtj article serves as the basis for the AMTA Online Course of the same name. To register for the course and receive continuing education hours and a certiﬁcate of completion for the Online Course, please visit www.amtaonlinetraining.org.
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