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CNS

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                                         Central Nervous System (functional regions)

CENTRAL NERVOUS SYSTEM aka CNS - is composed of the brain & spinal cord, which integrate, process, &
coordinate sensory data & motor commands. The expanded & specialized anterior nerve cord, or the brain, is the seat of
higher functions, such as memory, learning, & emotion. What are the made of? Both are composed of white matter and
gray matter. White matter is collections of myelinated axons. Gray matter is collections of unmeylinated axons an
neuron cell bodies. Some general CNS terms.

      center - collection of neuron cell bodies with a common function. A center with a discrete anatomical boundary is a
          nucleus.
      neural cortex - a thick layer of gray matter covering portions of the brain surface. The term higher centers refers to
          the most complex integration centers, nuclei, and cortical areas of the brain.
      tract - white matter of the CNS contains bundles of axons that share common origins, destinations, and functions.
          Tracts in the spinal cord form larger groups called columns.
      pathways - centers & tracts that link the brain with the rest of the body. For example, sensory pathways distribute
          information from peripheral receptors to processing centers in the brain, & motor pathways begin at CNS
          centers concerned with motor control and end at the effectors they control.

CNS Meninges

There are three “motherly” tissues or meninges [ = membranes ] that surround & protect the CNS. These are the dura mater,
pia mater, & arachnoid mater. The dura mater [ = hard mother ] is the outermost layer & is a tough, fibrous membrane. The
innermost layer, the pia mater [ = pious mother ] is a thin sheet directly over the spinal cord & brain. Along the innerside of
the dura mater is the arachnoid mater. It is a very thin membrane with numerous filaments that connect it to the pia
mater. These filaments resemble cobwebs, hence the “spider-shaped mother.” These 3 meninges protect the brain &
act as “safety belts.” A concussion is due to your brain sloshing to one side (objects in motion tend to remain in motion)
The void between the pia mater & arachnoid mater is the subarachnoid space, which is filled with cerebrospinal fluid.


                                              [AVERAGE SEXUAL DIFFERENCES IN THE CNS]
                             MALE                                                                FEMALE
on average better on visual-spatial tasks, mathematical              better on verbal tasks; recalling landmarks, & precise
reasoning, throwing & aiming objects                                 manipulation of objects
corpus callosum more cylindrical & uniform in diameter;              parts of the anterior commissure & corpus callosum are larger;
brain function is more lateralized—less communication between        corpus callosum is wider & more bulbous posteriorly—more
cerebral hemispheres                                                 communication between hemispheres
newborns greater motor strength & muscle tone                        infants greater sensitivity to touch, taste, & light; smile more
                                                                     often
tend to be more aggressive                                           tend to be more nurturing
in spinal cord, motor neuron clusters for genitalia much larger &    apparently better memories, especially in recalling names with
have receptors for testosterone but not estrogens                    faces
gray matter of R cerebral cortex is thicker than on the left         tend to have a longer left temporal lobe & larger visual cortex
brains larger by 16%, but density of neurons between sexes may
differ—females higher??; male’s brain shrinks faster in old age
(16%)
[SEX DIFFERENCES: In only a few cases have these sex differences in humans been confirmed by independent labs, and no
    information is available on the effects of endogenous or exogenous hormones on these sex differences, either developmentally or
    in adult life. However, there is growing evidence that fluctuations in adult hormone levels affect brain structure, and we must hold
    open the possibility that differences in gonadal hormone levels in the adult could contribute to some differences in brain structure.
    We do not have a great understanding of the functional significance of these structural sex differences. We do know that sex
    hormones do concentrate in particular regions that play an important role in aggression, courtship, & mating behaviors. ]


SPINAL CORD & ITS PNS PORTIONS
The spinal cord is an important information highway relaying information back and forth from the brain to the body and the
body to the brain. It is also involved in reflexes . It is about the diameter of your little finger (a bit bigger really). The
spinal cord gives off nerves along its course that supply the skin, muscles, bones, and orgaons of the body. IThe spinal
cord passes through a space made by the vertebral bones (the vertebral foramina,) which form the vertebral canal.
The central ‘H-shaped’ portion is the gray matter. The gray matter has anterior & posterior horns and a gray
commissure, which connects the R & L halves for communication. In the center of this is a small tube called the central
                                                                                                                                                             2
canal, which is filled with cerebrospinal fluid. Surrounding the gray matter is the white matter (myelinated), which carries
impulses up & down the length of the spinal cord. There are several descending & ascending tracts in the white matter
that carry these communicating impulses. Communication up & down the tracts are necessarily in the white matter
(myelinated) so that impulses move quickly.

Branching from the spinal cord are the dorsal & ventral roots. There is an enlargement of the dorsal root that is the
dorsal root ganglion, which is full of cell bodies. The ventral & dorsal roots connect to form a spinal nerve, which exits
the vertebral canal in between the vertebral pedicles through the intervertebral foramen. The sympathetic trunk is a
series of ganglia that connect to the ventral rami. There are 31 pairs of spinal Nn, 1 pair of sympathetic trunks, & 12 pairs
of cranial Nn. The sympathetic trunk is part of the sympathetic “flight or fight” responses of the autonomic nervous system
of the peripheral nervous system.

Incoming signals are carried by afferent (ad = towards) Nn, and exiting signals are carried by efferent (ex = away) Nn.
Dorsal roots are primarily sensory nerves, so they are afferent (ad = towards). The ventral roots are primarily motor
impulses, so they are efferent (efferent nerves act on effectors). One could say impulses go “in the back side & out the
belly side.” [ Think of the signal received & sent as a long-bladed knife that goes through your back and out your belly. Ouch. ]

Structure                                              General Innervation                                     Representative Nerves
Cervical Plexus (C1-C4)                                Mm and skin of neck & shoulder;                         phrenic innervates diaphragm
                                                       diaphragm
Brachial Plexus (C5-T1)                                upper extremity Mm & skin                               axillary, musculocutaneous, ulnar, median,
                                                                                                               radial
Lumbar Plexus (L1-L4)                                  lower extremity Mm & skin, perineal                     femoral, obturator, saphenous
                                                       Mm/skin; some abdominal Mm
Sacral Plexus (L4-S4)                                  lower extremity Mm & skin, perineal                     sciatic, tibial, fibular, gluteal, pudendal
                                                       Mm/skin
Intercostal/Thoracic Nerves                            Intercostal & Abdominal Mm, skin                        Intercostal nerve branches (rami)


[ Cervical Spinal Cord Injuries: because the nerves exiting the spinal cord correspond to various parts of the body, one can
  predict the effects of spinal cord injury on the body. ]
 [ Level                                      Injury if roots of level intact & cord above intact:
 C1-C2      that’s all for you; death is usually instantaneous
  C3        total quadriplegia; requires respirator because diaphragm is largely innervated by C4nerves (e.g. phrenic N)
  C4        can shrug shoulders; respirations weak but respirator not required
  C5        can move shoulder & flex elbow weakly (Deltoid & Biceps brachii innervation are roots C5 & C6 and C6 is lost)
  C6        patient can move own wheelchair, but cannot grasp objects; can flex arm
  C7        patient can barely hold onto objects; extend arm
  C8        digit flexors functioning, but grasp still impaired because manus intrinsic Mm not functioning; manus has a claw appearance
            because Lumbricals not working
   T1       upper extremity functions, but patient is paraplegic (cannot move lower extremities) ]; move pinky finger

The spinal cord narrows to a tip known as the conus medullaris [ middle cone; medulla = middle part (medius) ]. The spinal cord
ends with a terminal filament or filum terminale that is an extension of the pia mater, which anchors the spinal cord. In
an adult, the spinal cord ends at about L2 (the iliac crest is at about L4). Spinal taps for cerebrospinal fluid are done in
the lumbar region between L3-L4 so that the spinal cord is not damaged. When you’re young, the spinal cord fills up
your vertebral canal, but the spinal cord does not grow much during puberty, unlike the remaining body.

There are numerous ventral & dorsal roots at the end of the spinal cord, the cauda equina [ = horse tail ], which fill the
lumbar & sacral vertebral canal. The gray matter is much thicker in the lumbar region because of the numerous
branches of the cauda equina that come off of the lower portion of the spinal cord. The sacral roots have a long way to
travel in the vertebral canal; the spinal Nn & their split into dorsal & ventral rami actually occur in the vertebral canal. The
dura mater & cerebrospinal fluid end at about S2. Below in the epidural space is where saddle block (epidural) injections
are given for women in labor; there’s no worry of anesthetizing the CNS & labor pain is decreased, but leaves enough
feeling for the woman to know when to push.
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THE BRAIN is just really an enlarged anterior spinal cord with some new features added on by vertebrates.....
 [ This is your brain on biology class: zzzzzz........zzzzzz.........zzzzzz..........zzzzz ]

DIVISIONS OF THE BRAIN: divided into 4 basic regions
1. Cerebral hemispheres (cerebrum)
2. Diencephalon (thalamus and hypothalamus)
3. Brain stem=mesencephalon (midbrain), cerebral peduncles, corpora quadrigemina, pons, and medulla oblongata
4. Cerebellum

Divisions: forebrain, midbrain, hindbrain
   1. forebrain (aka prosencephalon) [ proso, forward; enkephalos, “in the head,” or “brain” ] - includes the cerebrum (aka cerebral
       hemispheres) and is particularly enlarged in humans [ humans are the most fat-headed animal (on this planet!). ].

     The cerebrum is folded tubes of tissue or convolutions. The convolutions are gyri [ gyrus = circle, as in gyrate ], and the
     grooves formed in between are the sulci & fissures (fissures are deeper than sulci; singulars are gyrus & sulcus) . The
     central sulcus & lateral fissure are major landmarks of the cerebrum. The cerebrum has four lobes named for the
     bones that cover these areas: the frontal, parietal, occipital, & temporal lobes.

     Why is your brain folded?
     Mnemonic courtesy of Jonathan Pettigrew: One sulks when feeling low/depressed; sulci are depressions in the brain.

     Particular areas of the brain perform specific functions. The precentral gyrus of the frontal lobe is the primary
     motor area, & the postcentral gyrus of the parietal lobe is the primary sensory area. These two areas straddle
     the central sulcus of the cerebrum. The primary motor & sensory areas can be mapped to parts of the body. In both,
     the pes area is medial & the head lateral. The premotor area of the frontal lobe is anterior to the primary motor area
     and it handles stereotyped movements, such as typing, writing, & hitting the snooze button when the alarm rings.

     Anterior to the premotor area is the prefrontal cortex, which is for “higher intellectual activities,” such as judgment and
     reasoning. The prefrontal cortex has extensive connections with other cortical areas & with other portions of the
     brain. Feelings of frustration, tension, & anxiety are generated at the prefrontal cortex as it interprets ongoing events
     & makes predictions about future situations or consequences.
     [ Some insects can live up to a year without their heads. If connections between the prefrontal cortex & other brain regions are severed, frustrations, tensions, &
          anxieties are removed. Earlier in this century up until the 1970’s, frontal lobotomy, was used to "cure" a variety of mental illnesses, especially those
          associated with violent or antisocial behavior. After a lobotomy, the patient would no longer be concerned about what had previously been a major problem,
          whether psychological (hallucinations) or physical (severe pain). However, the individual was often equally unconcerned about tact, decorum, & toilet
          training. Now that drugs have been developed to target specific pathways & regions of the CNS, lobotomies are no longer used to change behavior. ]

Cerebral Hemispheres (Cerebrum)
1. Superior portion of the brain, about 83% of total brain mass. What most people think about when you say brain.
2. Has a wavy/groovy appearance
        -waves are called gyri (ridges of brain tissue)
        -grooves are called sulci, the deepest grooves are called fissures & separate the brain into sections.
           longitudinal fissure separates the brain into left and right halves. transverse fissure separates the cerebral
           hemispheres from the cerebellum inferiorly.
3. The hemispheres are connected/divided by a structure composed of a bundle of white matter called the corpus
   callosum. Allows communication between the two cerebral hemispheres.
4. Some deep sulci divide each cerebral hemisphere into 5 major lobes: frontal, parietal, occipital, temporal, and insula
   lobes.

Cerebral Cortex is the superficial area of gray matter in the cerebrum.
1. Home of the conscious mind, controls self-awareness, voluntary movements, communication, memory, and
   understanding,
2. Consists mostly of gray matter, so mostly neuron cell bodies, dendrites, and very short unmyelinated axons.
3. Its is only 2-4mm thick, but its many convolutions triple the surface area, accounts for 40% of the total mass of the
   brain.
4. Described by functional regions, used to study by people or animals that had sustained local injury, now use PET
   scans (positron emission topography), MRI magnetic resonance imagery.

CEREBRAL WHITE MATTER:
• Lies underneath the outer layer of gray matter in the cerebral cortex where it allows communication between the
   different areas of the cerebral cortex and with the brain stem and spinal cord. Does this by the many axons that form
   the cerebral white matter. Most of these axons are myelinated and bundled into large tracts.
                                                                                                                                4
    Types of Tracts:
    1. Comissural: form connections between the 2 hemispheres allowing it to act as a whole (run horiz.), largest is the
       corpus callosum.
    2. Association fibers: connect different parts of the same hemisphere. (run horiz.)
    3. Projection fibers:descend form cerebral cortex to caudal portions of CNS or ascend from lower centers. (run
       vertically). Link the cerebral cortex to brain stem, cerebellum, and spinal cord This is how sensory info. reaches cortex
       and motor info. leaves.
    4. Cerebral/Basal Nuclei:are cell bodies (gray areas)that lie deep within the cerebral white matter. Composed of :
       caudate nucleus, the lentiform nucleus, and the amygdaloid body (limbic system)
             F(x) 's : aids cerebral cortex in starting, stopping, and coordinating volunatry mvts and their intensity or speed.

    Cerebral Cortex has 3 functional areas/regions...motor areas, sensory areas, and association areas.

Motor Areas-control voluntary motor functions
   1. The primary motor cortex (pmc) lies in the posterior part of the frontal lobe. Within the motor cortex is the primary
       motor cortex. Located on the precentral gyrus of the frontal lobe.
   2. In this area are large neurons called pyramidal cells, which have long axons that project to the spinal cord. There,
       they signal the spinal motor neurons to bring about the skilled and voluntary movements of the limbs, trunk, and so
       on.
   3. The axons of pyramidal cells form the massive pyramidal tract. Tract = a collection of nerve fibers in the CNS having
       the same origin, destination, and function. Descends thru the brain stem and through the spinal cord. See Fig. 13-
       12 & 9-7 “Decending Tracts”
   4. Axons from the Prmary Motor Cortex are contralateral-those from the left cortex control movements on the right side
       of the body and vice versa. See Fig. 13-12
   5. Broca's area lies anterior to the inferior region of the premotor cortex. "Preplans" voluntary mvts. and is associated
       with speech.

    Sensory Areas-involve conscious awareness of sensation and occur in the parietal, temporal, and occipital lobes. There
    is a distinct area for each of the major senses (sight, touch, hearing, etc.) See Fig. 10-4
    1. The primary sensory cortex is located along the postcentral gyrus of the parietal lobe, just posterior to the primary
    motor cortex.
    • It is involved with touch, pain, pressure, taste, and temp. receptors
    • responsible for conscious awareness of general somatic senses and determines the precise area where you sense it.
         (spatial discrimination). Fig. 10-10
    • Sensory info. is picked up by receptors in the bodies periphery, and sent to the spinal cord to the primary sensory
         cortex Fig. 10-9
    • Like the pmc it is contralateral Fig. 10-9
    • The most sensitive area on the body have large portions of Primary sensory cortex set aside for it. (face, lips, tongue,
         fingers). Fig. 10-9
    2. The visual cortex lies at the posterior tip of the occipital lobe and is the largest cortical sensory area. Allows you to
         see.
    3. The auditory cortex lies at the superior edge of the temporal lobe and gives you conscious awareness of sound.
    4. The olfactory cortex lies at the inferior edge of the temporal lobe and gives you conscious awareness of odors.
         Connected to an area called the Limbic system of the brain that is involved in producing emotions. Why smells often
         trigger emotional responses.
    5. The gustatory cortex lies near the post central sulcus and is involved with taste

    Association areas tie together or make associations between, the different kinds of sensory information and coordinate
       motor responses
    1. The premotor cortex controls learned motor skills, (playing piano, bike riding, typing, throwing a ball...)
    2. The visual association area surrounds the primary visual cortex, and allows an evaluation of what you are seeing.
       Uses past experiences to interpret incoming info. If you damage this area, you can still see, but you won't know what
       you are looking at.
    3. The prefrontal cortex lies in the anterior portion of the frontal lobe and is involved with reasoning and complex
       learning abilities called cognition and personality. Necessary for abstract ideas, judgement, social behavior, concern
       for others, and conscience (right from wrong). Lots of connections with the limbic system = the emotional part of the
       brain.
    4. The sensory association area lies posterior to the primary somatosensory cortex it integrates sensory inputs into a
       comprehensive evaluation of what is being perceived by sensory receptors. Ex. hand in pocket (uses stored
       memories). Has lots of connections to primary sensory cortex.
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The top layer of the brain that contains the sulci & gyri is gray matter, and most of the inner brain is white matter
(myelinated nerves; mazgi is a rich sweet bread dish). There are areas of gray matter inside called basal ganglia (ganglia =
mass of cell bodies). Commissural tracts [ commisura = join together; commit; Commissioner Gordon thought that my brain needed to be committed. ]
are pathways formed by myelinated nerve fibers that connect the R & L hemispheres. This is how the the 2 hemispheres
communicate so that they “left hand knows what the right hand is doing.” The nerve fibers decussate, which means they
cross over. This means that the left hemisphere controls the right side of the body and interprets information from the
right side and vice versa. The two main commissural tracts are the anterior commissure & the corpus callosum (which is
estimated to carry 4 billion impulses per second).

There are four ventricles [ = little bellies ] in the brain filled with cerebrospinal fluid: 1st, 2nd, 3rd, & 4th ventricles. The 1st
                                                                                       st    nd
ventricle is within the L hemisphere; the 2nd within the R hemisphere (the 1 & 2 are roofed by the corpus callosum &
                             rd                                                                                       th
floored by the fornix); the 3 surrounds the thalamus in the center of the brain (a sagittal cavity); and the 4 is roofed by
the cerebellum & floored by the medulla oblongata (a sagittal cavity also). These help to cushion, nourish, and protect the
brain from bumps and jolts.

     Ventricle Mnemonic [ courtesy of Matt Socha ]:
                                                                nd                    rd
     When pulling into an intersection, 1st look to your Left; 2 look to your Right; 3 look to the center of the intersection;
             th
         & 4 check behind you.
     [ A study of musicians trained at a very young age versus nonmusicians demonstrated that the musicians had a larger corpus callosum. The stimulus children
       receive the first 6-7 years of their lives greatly influences their brain growth and the potential they may reach throughout their lives. ]

The hypothalamus & thalamus are both parts of the forebrain. The thalamus relays afferent sensory impulses, and the
hypothalamus is the center for controlling emotions, autonomic function (smooth muscles, glands, temperature
regulation, etc.), & hormone production. A narrow stalk, the infundibulum, connects the hypothalamus to the pituitary
gland, the “master hormonal gland” of the endocrine system; the pituitary is in turn run by the hypothalamus. The
olfactory & optic Nn (cranial Nn I & II) branch from the forebrain.

[ Intelligent people have more zinc & copper in their hair. Leonardo da Vinci could write with one manus & draw with the other simultaneously! ]
FUNCTIONAL BRAIN SYSTEMS: are networks of neurons that span large distances within the brain. For this reason, it is impossible to
localize such systems to specific brains regions.

The limbic system functions to mediate emotional behavior related to survival and is, of course, associated with
pleasure & pain (memory & learning). The hippocampus with portions of the cerebrum also functions in memory.
Because of this relationship, events that cause a strong emotional response are committed to memory much more
efficiently. The limbic system has a primary function in emotions such as pain, pleasure, rage, fear, sorrow, sexual
feelings, docility, & affection. Olfactory sensations are sent to the rhinencephalon of the temporal lobe and to the
limbic system. This tie to basic memory is why smells can elicit such strong memories. Parts of the limbic system
include portions of the temporal lobe (hippocampus & amygdaloid body), fornix, olfactory bulb & tract, & mamillary
body of the hypothalamus.

The Reticular Activating System (RAS): is scattered throughout the medulla, pons, and midbrain and consists of a
complex network of fibers, and small scattered nuclei. The fibers connect the hypothalamus, basal ganglia, cerebellum,
and cerebrum with all major ascending and descending tracts. These widespread connections make reticular neurons
ideal for governing the activity of the nervous system as a whole. Certain reticular neurons, unless inhibited by other brain
areas, send a continuous stream of sensory impulses to the cerebral cortex that is believed to maintain the cortex in an
aroused, conscious state. Without arousal from the reticular formation, the cortex remains unaware of its surroundings.
The RAS acts as a filter for the flood of sensory inputs from all over the body. It’s literally bombarded by sensory inputs,
so we must have some way of filtering out information that is not important.

Repetitive, familiar, or weak signals are damped (filtered out), but unusual, significant, or strong impulses do reach our
cerebral cortex (consciousness). Between them, the RAS and cerbral cortex disregard perhaps 99% of all sensory stimuli
as unimportant. If this did not occur, the sensory overload would drive us crazy.

  [The drug LSD removes these sensory dampers, promoting similar type of sensory overload. Take just a moment to become aware of all the stimuli in your
      environment. Notice all the colors, shapes, odors, sounds, and so on. How many of these sensory stimuli are you usually aware of ? Remember the famous
      peyote seen in the movie Young Guns it has roughly the same effect]
[The activity of the RAS is inhibited by sleep centers, located in the hypothalamus and other neural centers, and is depressed by alcohol, sleep-inducing drugs,
or other agents. Severe injury to this system results in permanent unconsciousness (irreversible coma). Decreased activity of the reticular formation results
in sleep = state of changed consciousness from which a person can be aroused by stimulation. Although cortical activity is depressed during sleep, brain stem
functions (respiration, HR, and BP) continue. Even environmental monitoring continues to some extent, illustrated by the fact that strong stimuli (things that
go bump in the night) immediately arouse us. In fact people who sleepwalk can avoid objects and navigate stairs perfectly well while truly asleep. The need
for sleep is still a mystery, but has healthful effects. If deprived, get irritable, and exhibit personality disorders. When first entering sleep, mediated by the
hypothalamus, RAS activity declines and we lose motor control in certain areas like in the postural muscles ( head bob effect, slumping in chair, etc.). To keep
from falling asleep, its best to try to provide maximum sensory input: (taste, smell, vision, hearing etc...), although no amount of stimuli can replace a good
                                                                                                                                                                         6
night’s sleep. The Cerebral Cortex can activate the reticular formation: intense mental activity keeps person awake.]

[ Hemisphere specialization: The L hemisphere is usually the categorical hemisphere & the R the representational hemisphere. In most people, the L hemisphere
   contains the general interpretive & speech centers, and this is the hemisphere responsible for language-based skills. For example, reading, writing, & speaking are
   dependent on processing done in the left cerebral hemisphere. In addition, the premotor cortex involved with the control of manus movements is larger on the left
   side for right-handed than for left-handed individuals. The L hemisphere is also important in performing analytical tasks, such as mathematical calculations &
   logical decision making.
The R cerebral hemisphere analyzes sensory information & relates the body to the sensory environment. Interpretive centers in this hemisphere permit you to identify
   familiar objects by touch, smell, sight, taste, or feel; e.g., the R hemisphere plays a dominant role in recognizing faces & in understanding 3-D relationships. It’s
   also important in analyzing the emotional context of a conversation. For example, determining whether the phrase " Can’t you get lost?" was intended as a threat or
   question. Individuals with a damaged R hemisphere may be unable to add emotional inflections when speaking.
The L hemisphere is the categorical hemisphere in 96% of right-handed individuals. Left-handed people represent 9% of the human population. The L hemisphere is
   the categorical hemisphere in 70% of left-handed persons, and the R hemisphere in 15%; in the remaining 15%, there is no apparent specialization. Interestingly,
   an unusually high percentage of musicians & artists are left-handed. The complex motor activities performed by these individuals are directed by the primary
   motor cortex & association areas on the right (representational) hemisphere. ]

2. midbrain (aka mesencephalon) [ mesos = middle ]
The midbrain is a small central area that connects the forebrain to the hindbrain. Sensory nuclei, such as the superior &
inferior colliculi, in the midbrain process visual & auditory information and control reflexes triggered by these stimuli. [ For
example, your immediate, reflexive responses to a loud, unexpected noise (eye movements and head turning) are directed by nuclei in the midbrain. This region also
contains centers involved with the maintenance of consciousness. ] The Nn for the extrinsic eye Mm, the oculomotor & trochlear Nn (cranial
Nn III & IV), branch from the midbrain.

3. hindbrain (aka rhombencephalon) [ rhomb = hind ]
The hindbrain contains the cerebellum, pons, & medulla oblongata. The cerebellum is tightly folded tissue that receives
proprioceptive information from the spinal cord & monitors all proprioceptive, visual, tactile, balance, & auditory sensations
received by the brain [ “Get the Balance Right” ]. The pons [ = bridge ] is a mass of white matter (nuclei & tracts) that
bridges parts of the cerebellum & spinal cord to the rest of the brain. [ In addition to tracts & relay centers, the pons also contains nuclei
involved with somatic & visceral motor control. The cerebellum may be permanently damaged by trauma or stroke or temporarily affected by drugs, such as alcohol.
These alterations can produce ataxia (= lack of order), a disturbance in balance. In severe ataxia, the individual may be unable to sit or stand without assistance. ]


The medulla oblongata regulates basal metabolism (temperature, respiration, heart rate, digestion) & relays info to
the remaining brain stem & thalamus. Cranial Nn V-XII branch from the hindbrain. Note that the cranial Nn have no
sympathetic fx; the sympathetic trunk, which connects to the spinal Nn, handles these.
[ Researchers using mice have discovered that bone marrow stem cells can migrate into the brain & differentiate into neurons, but it may be years before it can be
  proven to be safe & effective treatment for human disorders (Dec. 2000). This process may be a repair mechanism that is always active. There are two types of bone
  marrow stem cells, and earlier studies have shown that they can differentiate into muscle, liver, & bone. ]

[ The brain can sometimes compensate for damage quite well, making new connections among surviving neurons. The dogma among human brain research has been,
  there’s no new neuron growth. The hippocampus is one site where the brain routinely makes new neurons. A concentration of stem cells differentiate into new brain
  cells. The hippocampus (part of the limbic system) is important in memory & learning. Because one continually has new memories, this finding is not surprising.
  (The hippocampus does not store memories, but helps to form them after receiving information from various regions. Stem cells in the hippocampus was known in
  rats back in 1965, but not verified in humans until 1998. Mammals (with such complex brains) have limited regenerative capabilities for neurons, but this recent
  discovery creates a great opportunity in brain repair research. ]

BLOOD BRAIN BARRIER
Nervous tissue has special metabolic requirements. Neurons only use glucose which must be supplied at a constant rate.
Neurons also need copious amounts of oxygen due to their high rates of metabolism (e.g., ATP production to transport
ions against their concentration gradients). The brain uses a constant supply of glucose—it does not shut off or turn down.
What happens to someone in solitary confinement for months or a little while in sensory deprivation tank? To meet the
oxygen & glucose needs of the neurons, about 15% of the blood pumped by the heart goes to the brain. Interruption of
the blood supply to the brain can have devastating results, and brain death occurs after only a few minutes without
oxygen. Progressive hypoglycemia leads to confusion, unconsciousness, & eventually death.

Because the brain is the main control center for the body, its cells must be protected from potentially harmful substances
in the blood (e.g., urea).
  - Capillaries in the brain are much less permeable than most capillaries elsewhere in the body and they exclude many
     molecules that cross capillary walls elsewhere. How? Capillaries form tight junctions.
  - These relatively impermeable capillaries form what is known as the blood-brain barrier.
  - This shelters the brain from fluctuations in the blood concentration of hormones, ions, & neurotransmitters. However
     lipid soluble substances can enter the ECF, bathing the neurons by simply diffusing through the cell membranes. This
     is one reason some antihistamines (Benedryl) make you sleepy. The older antihistamines readily crossed the blood
     brain barrier and acted on brain centers controlling alertness.
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The blood-brain barrier remains intact throughout the CNS with 4 noteworthy exceptions relating to the
endocrine system & the production of CSF:
  1. In a portion of the hypothalamus, the capillary endothelium is extremely permeable. This permeability exposes
      hypothalamic nuclei to circulating hormones and permits the diffusion of hypothalamic hormones into circulation.
  2. Capillaries in the posterior pituitary gland are highly permeable  secrete hormones.
  3. Capillaries in the pineal gland are also very permeable  secrete hormones.
  4. Capillaries at the choroid plexus are extremely permeable. Although the capillary characteristics of the blood-brain
      barrier are lost there, the transport activities of specialized ependymal cells within the choroid plexus maintain the
      blood-CSF barrier.


The Diffuse Modulatory System
The diffuse modulatory system is a set of neurons, which have widely dispersed connections. They are each
characterized by their use of a particular neurotransmitter (See Fig. 9-19 and Table 9-4)
Collectively, they modulate activity of great assemblies of postsynaptic cells (like much of cerebral cortex, multiple
thalamic nuclei, etc). This apparently enables them to mediate broad protracted actions/behaviors involving level of
arousal and mood (like falling asleep and perhaps falling in love). In addition, individual systems seem to be essential for
aspects of motor control, memory and learning, motivation, mood, or metabolic state (and probably a lot more that we
simply don't know about). What functions do each neuromtransmitter modulate?

Neurotransmitter                                                            Functions Modulated
Serotonin

Norepinephrine

Dopamine

Acetylcholine


Because of the small size of the nuclei and the diffuse (and often overlapping) projections of their axons, a structural lesion (trauma, stroke) involving
just one of these systems would be very unlikely. Thus clinicians do not think about these individual systems when localizing a lesion.What they do
recognize are conditions like prolonged coma, which are associated with bilateral lesions in the reticular formation of the pons and midbrain (involving
several of these systems simultaneously). However the diffuse modulatory systems can be individually affected in diseases (like Parkinson's disease) or
processes which target cells on the basis of their different transmitters or other unique biochemical features.




[Altered States of Consciousness] :

A conscious person is alert and attentive; an unconscious person is not. The difference may seem obvious, but there are many gradations of both.
The state of consciousness may be different from the commonly experienced wakefulness, drowsiness, and so on. Other, more bizarre situations,
such as those occurring with hypnosis, mind-altering drugs, and certain diseases, are referred to as altered states of consciousness. These altered
states are also characteristic of psychiatric illnesses.

Schizophrenia

One of the diseases that induces altered states of consciousness is schizophrenia, a disease in which information is not properly regulated in the
brain. The amazingly diverse symptoms of schizophrenia include hallucinations, especially "hearing" voices, and delusions, such as the belief that
one has been chosen for a special mission or is being persecuted by others. Schizophrenics do not usually have multiple personalities.
Schizophrenics can become withdrawn, are emotionally unresponsive, and experience inappropriate moods. They also experience abnormal motor
behavior, which can include total immobilization (catatonia). The symptoms occur in patterns that may or may not overlap.

The causes of schizophrenia remain unclear. Recent studies suggest that the disease reflects a developmental disorder in which neurons migrate
or mature abnormally during brain formation due to a genetic predisposition or multiple environmental factors that may include viral infections
and malnutrition during fetal life or early childhood. The brain abnormalities involve diverse neural circuits and neurotransmitter systems that
regulate basic cognitive processes. A widely accepted explanation for schizophrenia suggests that certain dopamine pathways are overactive. This
hypothesis is supported by the facts that the symptoms are made worse by amphetamine-like drugs, which are dopamine agonists, and that the
most therapeutically beneficial drugs used in treating schizophrenia block dopamine receptors. Schizophrenia affects approximately one in every
100 people and typically appears in the late teens or early twenties just as brain development nears completion. Currently there is no prevention
or cure for the disease, although the symptoms can often be controlled with drugs. In a small number of cases there has been complete recovery.

The Mood Disorders: Depressions and Bipolar Disorders

The term mood refers to a pervasive and sustained inner emotion that affects the person's perception of the world. In addition to being part of the
conscious experience of the person, it can be observed by others In healthy people, moods can be normal, elated, or depressed, and people
                                                                                                                                                       8
generally feel that they have some degree of control of their moods. That sense of control is lost, however, in the mood disorders, which include
depressive disorders and bipolar disorders. Along with schizophrenia, the mood disorders form the major psychiatric illnesses today.

In the depressive disorders (depression), the prominent features are a pervasive sadness; a loss of energy, interest, or pleasure; anxiety;
irritability; disturbed sleep; and thoughts of death or suicide. Depression can occur on its own, independent of any other illness, or it can arise
secondary to other medical disorders. It is associated with decreased neuronal activity and metabolism in the anterior part of the limbic system
and nearby prefrontal cortex. These same brain regions show abnormalities, albeit inconsistent ones, in bipolar disorders. The term bipolar
disorders describes swings between mania and depression episodes of mania, which are characterized by an abnormally and persistently elated
mood, sometimes with euphoria (that is, an exaggerated sense of well-being), racing thoughts, excessive energy, overconfidence, and irritability.
Although the major biogenic amine neurotransmitters (norepinephrine, dopamine, and serotonin) and acetylcholine have all been implicated, the
causes of the mood disorders are unknown.

Current treatment of the mood disorders emphasizes drugs and psychotherapy. The classical antidepressant drugs are of three types. The
tricyclic antidepressant drugs such as Elavil, Desyrel, and Pamelor, interfere with serotonin and/or norepinephrine reuptake by presynaptic
endings. The moneamine oxidase inhibitors interfere with the enzyme responsible for the breakdown of these same two neurotransmitters. A
third class of antidepressant drugs, the serotonin specific reuptake inhibitors (SSRIs), are the most widely used antidepressant drugs and
include Prozac, Paxil, and Zoloft. As their name—SSRI—suggests, these drugs selectively inhibit serotonin reuptake by presynaptic terminals.
In all three classes, the result is an increased concentration of serotonin and (except for the third class) norepinephrine in the extracellular fluid
at synapses. Since the biochemical effects occur immediately but the beneficial antidepressant effects appear only after several weeks of
treatment, the known biochemical effect must be only an early step in a complex, and presently unknown, sequence that leads to a.therapeutic
effect of these drugs.

Psychotherapy of various kinds can also be helpful in the treatment of depression. An alternative to drug therapy and psychotherapy is
electroconvulsive therapy (ECT). As the name suggests, pulses of electric current are used to activate a large number of neurons in the brain
simultaneously, thereby inducing a convulsion, or seizure. The patient is under anesthesia and prepared with a muscle relaxant to minimize the
effects of the convulsion on the musculoskeletal system. A series of ECT treatments alters neurotransmitter function by causing a down-
regulation of certain postsynaptic receptors. Another non-drug therapy used for the type of depression known as seasonal affective disorder (SAD)
is phototherapy in which the patient is exposed to bright light for several hours per day.

A major drug used in treating patients with bipolar disorder is the chemical element, lithium, sometimes given in combination with
anticonvulsant drugs. It is highly specific, normalizing both the manic and depressing moods and slowing down thinking and motor behavior
without causing sedation. In addition, it decreases the severity of the swings between mania and depression that occur in the bipolar disorders. In
some cases, lithium is even effective in depression not associated with manias. Lithium may interfere with the formation of members of the
inositol phosphate family, thereby decreasing the postsynaptic neurons' response to neurotransmitters that utilize this signal transduction
pathway.



    CNS Structure                                         Fxs of around 100 billion neurons & 1,000 billion neuroglia
FOREBRAIN (fig. 9-10)       You will be required to know this table in lecture.

  olfactory bulb & tract    transmit sensory input for olfaction

  optic nerve               transmits visual sensory impulses to the brain
                            crossing over of optic Nn impulses to both hemispheres occurs here (visual impulses decussate; the L picture
  optic chiasm
                                of the L eye & the L picture of the R eye go to the L hemisphere, & mirror ditto for R side)
                            endocrine gland that secretes the hormone melatonin, which regulates circadian (daily) rhythms
  pineal gland

  thalamus                  main relay station for afferent sensory impulses to the cerebrum (ad + fero = lead towards; incoming impulses)
                            control center for autonomic functions; control center for hormone production; control center for emotions
  Hypothalamus (Table           (autonomic fxs: Activation of sypatheic N.S. (catecholamine release from adrenal medulla; maintains [BG] thru
  9-2)                          effects on endocr. pancreas), temperature regulation (shivering & sweating), hunger (saiiety & feeding center), body
                                osmolarity (thirst and drinking behavior, secretion of vasopression), diurnal rhythms,
                                waking/sleeping patterns, and hormone production & balance

  mamillary body            controls olfactory reflexes      (it’s part of the limbic system)

  pituitary gland           secretes hormones that control growth, sexual maturity, & sexual cycles
                            fluid filled chambers that circulate cerebrospinal fluid to nourish & protect nerve cells; contains choroid plexi
  1st-3rd ventricles
                            [ = membrane braid ]; choroid plexus: net of vessels & neuroglial cells in the ventricles that make cerebrospinal
                           fluid

Cerebrum (Fig.9-15)         composed of 2 cerebral hemispheres; controls higher brain fxs; seat of intelligence & personality

   cerebral lobes:          frontal (personality, movement), temporal(smell/taste/hearing), occipital (vision), & parietal (sensory interpretation)

   precentral gyrus of      primary motor center for skeletal M m control (primary motor cortex)

      the frontal lobe      Is skeletal M in- or voluntarily controlled?   Is more brain mass used to run the manus or elbow?

      --- central sulcus    groove between the frontal & parietal lobes that divides the precentral & postcentral gyri
                                                                                                                                                                          9
     postcentral gyrus         primary processing center of sensory impulses; receives sensory input for touch, proprioception, pain, & temperature
       of the parietal          (primary sensory cortex.) Note the size of the cortical area that maps to a specific body region is proportional to the
       lobe                     number of receptors for that region.     See Fig. 10-10
     basal nuclei (fig.9-
        11) (ganglia)          areas of gray matter within the white matter of the cerebral hemispheres; regulate movement
     rhinencephalon of
      the temporal lobe        processes olfactory sensory input
                               interconnected structures at base of the cerebrum that control emotion and are important in memory & learning
     limbic system
                                  (pain/pleasure); parts include mamillary bodies, olfactory bulb & tract, fornix, thalamus, & parts of temp. lobe

     Corpus callosum           white matter tract that relays impulses between R & L hemispheres;                    Why is the corpus callosum white?
     fornix                    white matter tract of the limbic system that relays impulses between hemispheres [ connects hippocampus to
                                   hypothalamus ]

MIDBRAIN                       relay center: relays motor impulses from cerebrum to pons & sensory impulses from spinal cord to thalamus

      sup. & inf. colliculi    controls visual & auditory reflexes

      cerebral peduncles       connects the cerebrum to the spinal cord; carries ascending sensory information to the thalamus

      cerebral aqueduct        connecting canal for circulating cerebrospinal fluid between 3rd & 4th ventricles

HINDBRAIN                      relay center; controls basal fxs
                               controls muscular coordination & sense of balance (receives proprioceptive impulses from the spinal cord & monitors
      cerebellum
                                   all proprioceptive, visual, tactile, balance, & auditory sensations received by the brain)

      4th ventricle            circulates cerebrospinal fluid to nourish & protect nerve cells of brain; contains a choroid plexus

      pons                     relays impulses between cerebellar hemispheres & between medulla oblongata & thalamus
                               regulates basal metabolism & autonomic fxs; relays motor & sensory impulses to the remaining brain stem &
      medulla oblongata
                                   thalamus; autonomic function control: respiration, swallowing, vomiting, heart rate, blood pressure, digestion, etc.

Spinal Cord                    relays impulses between brain & remaining body & controls a multitude of reflex arcs

      central canal               circulates cerebrospinal fluid in spinal cord to nourish & protect nerve cells
[ It’s a myth that we only use 10% of our brains. Think about all the different regions of specialization that take up space & are used—even simultaneously! When
        you listen to a joke, a dozen or more areas of your brain may become active. It is safe to say we don’t know the capacity of the brain and that much of memory
        becomes difficult to access or simply inaccessible (lost addresses or erased??).
 A concussion is abrupt but temporary loss of consciousness (seconds to hours) resulting from a blow to the head or sudden stopping of the head that sloshes the brain
        around. A contusion is a visible bruising of the brain due to trauma & blood leaking from microscopic vessels. The pia mater may tear so that blood enters the
        subarachnoid space, and the frontal lobe is more commonly affected. A contusion usually results in immediate loss of consciousness (usually less than 5mins),
        loss of reflexes, transient cessation of breathing, & low blood pressure. A laceration is a tearing of the brain, usually from a skull fracture or gunshot wound. A
        large blood vessel is ruptured with bleeding into the brain & subarachnoid space. Consequences include hematoma (pooled blood that swells against the brain
        tissue), edema, and increased intracranial pressure.
 Melatonin is made from the neurotransmitter serotonin. Melatonin production peaks at night. In other mammals, melatonin slows the maturation of gametes &
        reproductive organs. In humans, melatonin production decreases at the onset of puberty, and pineal tumors that are removed cause premature puberty in
        children. Melatonin is a good antioxidant & may protect CNS cells from nitric oxide & hydrogen peroxide. Because its production cycles throughout the day,
        melatonin may establish or maintain daily changes in the physiological clock. Too little sunlight (from winter dark months at high latitudes or high cloud cover)
        may cause increased melatonin levels. This has been suggested to cause seasonal affective disorder (SAD), which is characterized by changes in mood, eating
        habits, & sleeping patterns. In sheep, which have a very large pineal gland, it contributes to the regulation of seasonal breeding—imagine hitting “puberty”
        every spring!




CRANIAL NERVES
                                     (You should know this table precisely..Does it look familiar??)
                                                                                                                           General                  Parasympathetic
CN               Name                                     General                                Sensory                    Motor                        Motor
 #                                   Mnemonic                           Mnemonic               Innervation               innervation                  Innervation
                                     (Remember......)   Innervation


 I       olfactory N                 On                 Sensory         Some                   from olfactory                   ---                           ---
         [ smell no evil ]                                                                       epithelium
                                                                                                  (smell)
                                                                                                                                                                   10

 II      optic N                    Old            Sensory            Say                 from optic disk @                 ---                          ---
         [ see no evil ]                                                                     retina (sight)


 III     oculomotor N               Olympus        Motor              Marry                       ---           Extrinsic Eye Muscles        Involuntary Mm of
         [ “eye mover” ]                                                                                        = Med., Inf., & Sup.         ciliary body & iris
                                                                                                                Rectus Mm; Inf.
                                                                                                                oblique; & Lev.
                                                                                                                palpebra

 IV      trochlear N                Towering       Motor              Money                       ---           Sup. oblique M of eye                    ---
         [ “pulley” ]

 V       trigeminal N               Tops                                                   face, mouth, &       Masseter, Temporalis,
         [ “3-twin;”                               Both (mixed)       But                   2/3 of tongue       etc. mastication Mm                      ---
                                                                                                  ---
         maxillary,
         mandibular, &
         opthalmic
         branches ]

 VI      abducens N                 A              Motor              My                          ---           Lateral rectus M of                      ---
         [ “lead away” ]                                                                                        eye


VII      facial N                   Finn           Both (mixed)       Brother                     taste               all facial Mm,         Glands: submandibular
                                                                                            [ to ant. 2/3 of       including Platysma        & sublingual salivary,
                                                                                                tongue ]                                     lacrimal


VIII     auditory N; aka            And            Sensory            Says                 equilibrium and                  ---                          ---
         vestibulocochlear N                                                                  hearing

 IX      glossopharyngea            German         Both (mixed)       Bad                        taste                                        parotid salivary
         l N                                                                               [ to post. 1/3 of    Pharynx Mm                    gland
                                                                                            tongue ] 1/3 of
         [ “tongue-throat” ]
                                                                                                tongue,
                                                                                           pharynx, middle
                                                                                                   ear

 X       vagus N                    Viewed         Both (mixed)       Business                   taste          Pharynx & larynx Mm           heart , lungs, &
         [ “wanderer,                                                                                                                        abdominal viscera
                                                                                            [ in pharynx ]
         vagrant” ]
                                                                                          pharynx, larynx,
                                                                                          heart, lungs, and
                                                                                             abdominal
                                                                                               viscera


 XI      spinal accessory           Some           Motor              Marry                       ---           Sternocleidomastoid &                    ---
         N;                                                                                                     Trapezius Mm
         aka accessory N

XII      hypoglossal N              Hops           Motor              Money                       ---           Tongue Mm                                ---
         [ “under tongue” ]

[CRANIAL Nn] Health care professionals often assess head injuries by asking the patient to demonstrate the actions mediated by these cranial nerves. If the patient
can or can’t do a certain action, more assessment is warranted.
Olfactory N (I) - beneath the frontal lobe; sends branches through cribriform plate into nasal cavity. Sensory for smell.
Optic N (II) - large nerve passing through optic canal & into eyeball. Sensory for sight.
Oculomotor N (III) - found in orbit, innervates most of the extrinsic eye Mm: Sup. rectus, Inf. rectus, Med. rectus, Levator palpebra, & Inf. oblique Mm.
Trochlear N (IV) - found in orbit, innervates Sup. oblique—the muscle that passes through a trochlea.
Trigeminal N (V) - main nerve of deep face, has three divisions:
           V1: Opthalmic division - passes up into orbit through sup. orbital fissure.
                     Frontal N - passes through top of orbit above eye, exits supraorbital foramen & becomes supraorbital N.
                              Supraorbital N - branch of frontal N out supraorbital foramen. Innervates skin of forehead.
           V2: Maxillary division - deep in maxillary bone.
                     Infraorbital N - exits infraorbital foramen with infraorbital A to supply skin of central face.
           V3: Mandibular division - passes down to mandible.
                     Inf. alveolar N - enters mandibular foramen & passes through mandible with inf. alveolar A. It exits mental foramen & becomes mental N.
                              Mental N - continuation of inf. alveolar N & innervates chin skin (mentum = chin).
                     Lingual N - passes between tongue & mandible to supply sensory to tongue.
Abducens N (VI) - found in orbit; innervates Lateral rectus.
                                                                                                                                                                 11
Facial N (VII) - emerges deep to parotid gland & divides into many branches which spread out over face.
Auditory N (VIII, aka Vestibulocochlear N) - to inner ear, deep in temporal bone. Sense for hearing & balance.
Glossopharyngeal N (IX) - descends med. to styloid process; supplies Stylopharyngeus & pharynx & post. tongue. Sensory for pharyngeal taste buds.
Vagus N (X) - runs down neck in carotid sheath w/internal jugular V & common carotid A. Parasympathetic innervation of heart & abdominal viscera.
Spinal accessory N (XI) - pierces back of Sternocleidomastoid & innervates it. Crosses post. triangle of neck to deep side of Trapezius to innervate it.
Hypoglossal N (XII) - found near post. belly of Digastricus, passes down & around Ext. carotid A, then forward below tongue between Mylohyoid & Hyoglossus.
                       Motor nerve to tongue.


[ Testing Cranial Nn & Speech: Laryngeal Mm control pitch & expiratory Mm control loudness, but there are many other factors controlling speech quality, such as lip,
       tongue, oral cavity, & pharyngeal cavity movement. For example, making the KLM sounds. “Kuh, kuh, kuh” tests soft palate elevation & Levator palati is
       innervated by CN X. “La, la, la” tests the tongue (CN XII), & “me, me, me” tests the lips (CN VII).
  The spinal accessory N is not really a “cranial N;” it originates from segments C1-C6, passes up through the foramen magnum, touches the vagus N, & then exits the
       jugular foramen. Some consider fibers of the spinal accessory to join the vagus, but others do not. ]

				
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