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PowerPoint Presentation by HC1208072085

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									THE NERVOUS
  SYSTEM
Divisions of the nervous system
    Protection of the Brain: The Cranial Meninges
•    Cranium is covered with protective membranes =
     meninges
      – Cranial meninges are continuous with spinal
          meninges
      – 3 layers: 1. outer, fibrous dura mater – forms sheets
          (falx) that separate the cerebrum and the cerebellum
          into the hemispheres and the cerebellum from the
          cerebrum
      – comprised of an outer endosteal layer and and inner
          meningeal layer
      2. middle arachnoid mater – avascular layer
          -named for the spider-like struts (trabeculae) that
          connect the arachnoid to the underlying pia mater
      3. inner, thin pia mater – vascular connective tissue
          -makes direct contact with brain tissue
          -cells of the pia mater are impermeable to the passage
          of many substances
          -this membrane is pierced by tiny capillaries that
          nourish the brain tissue – arise from the larger
          capillaries that travel within the dura mater
•large spaces for the circulation
of blood can be found between the
two dural layers = sinuses
e.g. superior sagittal sinus
• also large veins run through the
subarachnoid space
e.g. cerebral veins




                                     -there are spaces between these
                                     membranes
                                                     A. subarachnoid space:
                                                between the arachnoid and pia
                                                maters
                                                     -for the circulation of CSF
                                                     B. subdural space:
                                                between the arachnoid and the
                                                dura mater
                                                  C. epidural space – between
    Medical Application
•   Pathology
     –   There are three types of hemorrhage involving the meninges
     –   Epidural bleeding is rapid because it is usually from arteries, which are high pressure.
           •   Epidural bleeds from dural arteries can grow until they reach their peak size at six to eight hours post
               injury, spilling from 25 to 75 ml of blood into the epidural space
           •   the bleeding strips the dura from the inside of the skull, causing an intense headache.
           •   the bleeding is usually restricted to defined locations as its expansion stops at skull's sutures, where the
               dura mater is tightly attached to the skull.
           •   Bleeding into the epidural space in the spine may also cause epidural hematoma. These may arise
               spontaneously (e.g. during childbirth, or as a rare complication of anaesthesia (such as epidural
               anaesthesia)
           •   bleeding is likely to be venous.
           •   may present as pain, muscle weakness, or bladder and bowel dysfunction.
           •   estimates vary from 1 per 10,000 to 1 per 100,000 epidural anaesthetics
     –   A subarachnoid hemorrhage is acute bleeding under the arachnoid; it may occur
         spontaneously or as a result of trauma.
     –   A subdural hematoma is located in a separation of the arachnoid from the dura mater.
           •   subdural bleeding usually results from tears in veins that cross the subdural space.
           •   This bleeding often separates the dura and the arachnoid layers.
           •   Subdural hemorrhages may cause an increase in intracranial pressure (ICP), which can cause
               compression of and damage to delicate brain tissue.
•   the blood may be aspirated surgically to remove the mass and reduce the pressure it
    puts on the brain
     –   The hematoma is neurosurgically evacuated through a burr or craniotomy.
     –   The diagnosis of epidural hematoma requires a patient to be cared for in a facility with a
         neurosurgeon on call to decompress the hematoma if necessary and stop the bleed by ligating
         the injured vessel branches.



                                                                                                   subarachnoid
                                                                                                   hemorrhage
    Protection of the Brain: CSF
– CSF: 80 to 150 mL of clear, colorless liquid
    • replaced completely up to three times per day
    • glucose, proteins, lactic acid, urea, ions
    • made by specialized cells in the lateral ventricles – choroid plexus
         – networks of capillaries in the walls of the ventricles
         – covered by ependymal cells (epithelial) cells) that filter the blood plasma and produce CSF by
           secreting it
         – these cells are capable of allowing passage of certain substances from the blood through them
           into the CSF – inhibit the passage of others
    • continually circulates – ventricles of the brain and central canal to subarachnoid space
    • functions:
         – 1. Chemical protection: provides an optimal chemical environment for neuronal signaling
         – 2. Mechanical protection: acts as a shock absorber, preventing direct physical contact between
           brain tissue and the bones of the cranium or vertebral canal
         – 3. Circulation: allows the exchange of nutrients and waste products between the blood and
           nervous tissue
     Flow of CSF




-CSF forms in the choroid plexi of the lateral ventricles and flows into the 3 rd ventricle through the interventricular
foramina
-the 3rd ventricle adds to the CSF volume
-the CSF then flows into the 4th ventricle via and cerebral aqueduct (passes through the midbrain) – contributes more
volume
-then enters the subarachnoid space via openings in the 4 th ventricle called apertures
-also enters the central canal of the SC
-circulation is driven by ciliary action and pressures provided by the blood and gravity – 10 mm Hg
Circulation of the CSF
           •CSF is gradually reabsorbed into the
           blood through fingerlike projections
           into the dural venous sinuses = arachnoid
           granulations
           -absorbed at about 20ml/hr which equals
           its rate of formation




              •interfering with the drainage of CSF
              into the subarachnoid space can result
              in accumulation of CSF in the ventricles
              & CSF pressure rises = hydrocephalus
              (implantation of a shunt – lateral ventricle
              into the superior vena cava or abdomen)
         Blood-Brain Barrier (BBB)
•   within the body the capillaries are sites of exchange between materials in the blood and
    the ECF – filtration of the blood plasma by capillary cells helps form the ECF
•   most locations within the body, this exchange is very free
     –   the capillary walls are formed of a single layer of cells = endothelium
     –   the cells are joined loosely and are connected by numerous gap junctions and pores between
         the cells
     –   this allows for an easy diffusion of many plasma components (except large plasma proteins)
         between the cells themselves
     –   so even small changes in blood plasma contents can dramatically effect the ECF composition
•   however, in the brain, the capillary cells are careful as to what is filtered out of the blood
     –   the cells of the endothelium are very tightly linked together
     –   the cells are joined by tight junctions to restrict the flow of materials among them and through
         them into the ECF surrounding the brain
     –   so materials must directly passage the cells themselves to contribute to the ECF
     –   so the passage of things like glucose, amino acids, ions are carried through the cells by carrier
         proteins
     –   But lipid-soluble materials and gases (oxygen) can cross easily through the PM of the
         endothelial cells
     –   so transport between the cells is Anatomically Prevented and transport through the cell is
         Physiologically Restricted = BBB
     –   role of astrocytes in the BBB: 1. signal the capillaries to “get tight”
           • 2. participate in the transport of some ions like K+
          The blood supply to the brain
• Arterial blood reaches brain via internal carotid, vertebral arteries
• Venous blood leaves via internal jugular veins
-transient ischemic attacks (TIA): no permanent neurologic damage
          -temporary cerebral dysfunction caused by impaired blood
          flow to the brain
          -dizziness, weakness, blurred vision, slurred speech,
          paralysis
          -persists from 5 to 50 minutes
          -caused by emboli (blood clots), atherosclerosis

-cerebral vascular accident (CVA): stroke
          -affects 500,000 people per year
          -third leading cause of death
          -permanent cerebral dysfunction caused by impaired blood
          flow to the brain
          -sudden onset of symptoms
          -caused by cerebral hemorrhage (anuerysm), blood clot, atherosclerosis
          -treatment – rapid administration of clot-dissolving drugs (e.g. tPA) if stroke
          is caused by a clot
Neuronal Organization
       Neural Organization: Pathways
•A neural pathway is comprised of centers/cell bodies and
tracts
• Sensory pathway
   – Ascending
   – Information from sensory receptors to CNS
• Motor pathway
   –   Descending
   –   Information from CNS to skeletal muscle or glands
   –   Direct pathways – cause precise, voluntary movements
   –   Indirect pathways – result in involuntary movement (from brain
       stem)
  Major Regions of the Brain
Figure 15.1 Major Divisions of
           the Brain
Major Regions of the Brain
      Major Regions and Landmarks
• Cerebrum = largest portion
       -left and right cerebral hemispheres divided by the longitudinal fissure
       -connected by the corpus callosum
       -folded into ridges and grooves: grooves = sulci
                 -sulci divide the cerebrum into lobes
                 -ridges = gyri (gyrus)



    –Central sulcus
        •Frontal and parietal
        lobes
Major Regions and Landmarks
                 -outer layer of the cerebrum =
                 cerebral cortex
                 -area for specific processing of
                 sensation, -area of voluntary
                 movement, speech, all thought
                 processes

                 -motor and sensory areas
                 e.g. primary visual, auditory &
                 gustatory areas
                 e.g. primary motor area
                 (precentral gyrus): controls
                 voluntary contractions
                 -plus association areas for
                 integration and analysis of
                 incoming info & help in
                 making of “decisions”
The Cerebrum   -cerebrum is comprised of:
                1. white matter - neurons with
                  long, myelinated axons
                 -organized into tracts
               A. Association tracts: conduct
                    impulses between gyri within
                    a hemisphere
               B. Commisural tracts: connects
                    gyri in one hemisphere to
                    others in the other hemisphere
                    1. corpus callosum
                    2. anterior commisure
                    3. posterior commisure
               C. Projection tracts: tracts that connect
                     cerebrum to the lower parts of the
                     CNS (e.g. Thalamus, brainstem)

                2. gray matter – outer edge of the
               cerebrum = cerebral cortex (2-4 mm
               thick = billions of neurons)
               -localized areas of gray matter
               called the basal ganglia
-nuclei found deep within the cerebrum
  - links to the midbrain
                                                                           Basal Ganglia
  - receives input from the cortex & provides output to the motor areas of the cortex via the thalamus
 -integrates motor commands
 -regulates the initiation & termination of muscle mve.
 -also functions to anticipate body movements & controls subconscious contraction of skeletal muscle
•   comprised of the:
•   1. striatum
      –   caudate nucleus: activity occurs prior to eye movements
      –   putamen: precedes or anticipates body movements
      –   nucleus accumbens
•   2. globus pallidus: regulates muscle tone for movements
•   3. claustrum
•   4. substantia nigra: high concentration of dopanergic neurons
•   5. subthalmic nucleus
 Medical application: Basal Ganglia

-damage to the basal ganglia:
      -results in uncontrollable, abnormal body movements
      -muscle rigidity may develop and tremors
      -Parkinson – neurons that extend from the substantia nigra
               to the caudate nucleus and putamen
              degenerate
              -loss of dopamine releasing neurons – increase in
              muscle tone and stiffness
      -Huntington - hereditary disorder
              -caudate nucleus and putamen degenerate with loss
              of neurons that release GABA or ACh
              -spasmatic muscle contractions and loss of mental
              status
Integrative Functions and the Reticular Activating
                     System
•   integrative function of the cerebrum
     – processing of sensory information (analysis and storage) and making a decision
•   includes sleep and wakefulness, learning and memory, emotional responses
•   wakefulness/sleep: role of the RAS
     – 24 hr cycle called circadian rhythm
     – established by the hypothalamus and epithalamus
     – transition between the states of sleep and wakefulness is controlled by the RAS
     – portion of the cerebral cortex that is activated upon sleep arousal
     – when active – transmission of signals to many areas of the cortex both directly and via the
       thalamus = general increase in cortical activity
     – arousal = awakening from sleep
          • stimulation of the RAS – by touch, pressure, pain, light
          • no input by olfactory receptors!!
          • stimulation of cholinergic neurons that release AcH
     – sleep = state of altered consciousness from which you can be arouse
          •   exact function is still unknown
          •   two components: NREM and REM
          •   NREM – four stages
          •   REM – 3 to 5 episodes per 7 to 8 hour sleep period (10-20 minutes)
          •   regulated by many areas of the brain – hypothalamus, forebrain, medulla oblongata
          •   sleep inducer – adenosine – binds to receptors and inhibits the RAS (inhibits arousal)
          •   caffeine – binds to adenosine receptors and blocks their action – activity of the RAS is maintained
     Integrative Functions
• learning and memory
    – learning = the ability to acquire new information
        • no completely satisfactory explanation
    – memory = the process by which information that is acquired through learning is
      stored and retrieved
    – role for long-term potentiation (LTP) – enhances transmission at the hippocampus
      after a period of high-frequency stimulation
    – role for glutamate = binds NMDA glutamate receptors on post-synaptic neurons
        • different categories of memory
             – 1. immediate: ability to recall ongoing experiences, provides perspective to the present time
               so we know where we are and what we are doing
             – 2. short-term: temporary ability to recall information - seconds to minutes old
                   » e.g. look up a phone number and then dial it a few seconds later
                   » hippocampus, mamillary bodies of the hypothalamus and the anterior and medial nuclei
                     of the thalamus
             – 3. long-term: transfer of short-term into a more permanent type
                   » last from days to years
                   » e.g. use the telephone number enough – stored permanently
                   » role for the basal ganglia, cerebral cortex and cerebellum
• http://www.nlm.nih.gov/medlineplus/memory.html
• http://en.wikipedia.org/wiki/Anterograde_amnesia
• http://en.wikipedia.org/wiki/Retrograde_amnesia
         Major Regions and Landmarks
• Diencephalon
   – includes the hypothalamus, thalamus,
     epithalamus and subthalamus
   – thalamus: 80% of the diencephalon
       • paired oval masses of gray matter
         organized into nuclei, interspersed
         with white matter
       • joined by the intermediate mass
         (gray matter) in about 70% of brains
       • major relay station for most sensory
         impulses from the SC, brain stem
       • crude perception of pain, heat and
         pressure (refined in cerebrum)
       • transmits motor information from
         cerebellum to the cerebrum
       • relays nerve impulses to and from
         different areas of the cerebrum
       • seven major groups of nuclei !!!
•hypothalamus
   -Emotions, autonomic
   functions, hormone production
   -mamillary bodies – serve as
   relay stations for reflexes
   related to eating
   -supraoptic and preoptic
   nuclei that in hormone
   secretion (ADH) and body
   temp
   -major functions:
   1. control of the ANS –
   integrates signals from the
   ANS (regulated smooth and
   cardiac muscle contraction)
    major regulator of visceral
   activities (heart rate, food    3. regulates emotional and behavioral patterns – rage,
   movements, contraction of       aggression, pain and pleasure + sexual arousal
   bladder)                        4. regulates eating & drinking – hypothalamus contains
   2. produces hormones &          a thirst center which responds to a rise in osmotic
   connects with pituitary to      pressure in the ECF (dehydration)
   regulate its activity           5. controls body temperature – monitors temp of blood
                                   flowing through the hypothalamus
•epithalamus – consists of the pineal gland and habenular nuclei
        -pineal gland – part of the endocrine system
                       -secretes the hormone melatonin
                       -increased secretion in dark
                       -promote sleepiness and helps set the circadian
                       rhythms of the body (awake/sleep period)

•subthalamus – works with the cerebrum and cerebellum to control body
       movements
       -majority is made of the subthamic nuclei
       -sends efferent connections to the caudate nucleus and putamen,
       to the medial and lateral nuclei of the thalamus and to the red
       nucleus and substantia nigra of the midbrain
       -also receives afferent connections from the substantia nigra
              Major Regions and Landmarks
    BRAIN STEM
•   Medulla oblongata
     –   continuation of the SC that forms the inferior part of
         the brain stem
     –   relays sensory information and controls automatic
         motor functions
     –   where the SC and MO meet - 90% of the axons from
         the right side of the SC cross over to the left side of the
         MO and vice versa = decussation
     –   white matter contains sensory/ascending and
         motor/descending tracts
     –   some of the white matter form bulges called pyramids
         – white tracts that connect the cerebrum to the SC
     –   contains several nuclei also that regulate autonomic          -associated with 5 pairs of
         functions - reflex centers for regulating heartbeat and
         BP (cardiovascular center), respiration (respiratory          cranial nerves
         center), plus vomiting, coughing, sneezing, hiccuping         VIII
         and swallowing
     –   nuclei in the posterior part are associated with
                                                                       IX
         sensations of touch, proprioception, pressure and             X
         vibration                                                     XI
                                                                       XII
-other nuclei
          1. inferior olivary: part of the
          olive
          -relay impulses from proprioceptors
          to the cerebellum – joint and muscle
          position
          2. gracile: ascending sensory tracts
          from SC synapse here
          -relayed to the thalamus by
          postsynaptic neurons
          3. cuneate: ascending sensory tracts
          from SC synapse here
          -relayed to the thalamus by
          postsynaptic neurons                   -injury to the medulla: hard blow to the
                                                 back of the head or upper neck can be
                                                 fatal
                                                 -damages the medullary rhythmicity
                                                 area of the respiratory center (disrupts
                                                 pattern of breathing)
                                                 -non-fatal injury: paralysis and loss of
                                                 sensation, irregular breathing and heart
                                                 rate
         Major Regions and Landmarks
  BRAIN STEM
• Pons
  = “bridge”
  - e.g. connects brain stem to the cerebrum
     via bundles of axons
  - superior to the medulla and anterior to the
     cerebellum
  – consists of nuclei (cell bodies in gray
     matter) and tracts
  – somatic and visceral motor responses
      • Pontine nuclei – control voluntary
        movements that originate in the cerebral
        cortex and are relayed through the pons
        into the cerebellum
      • Pneumotaxic area – controls breathing
        (with medulla)
      • Apneustic area – controls breathing (with
        medulla)
        Major Regions and Landmarks
 BRAIN STEM
• Midbrain (Mesencephalon)
   – relay station between the cerebrum and the
     spinal cord
   – extends from the pons to the diencephalon
   – sends motor tracts to the SC, medulla and
     pons & conducts sensory tracts to the
     thalamus
   – anterior portion contains a pair of white
     tracts = cerebral peduncles
        • conduct impulses from the cerebrum to the
          SC, pons and medulla
   – posterior portion = tectum
        • white matter tracts = cerebellar peduncles
        • four round elevations = colliculi
        • reflex centers for visual activities (tracking,
          scanning) pupillary reflex, shape of the lens     -generates involuntary somatic
        • reflexes that mediate movements of the eyes,
          head and neck - the startle reflex                motor responses
        • relays impulses from hearing receptors to the         •release of dopamine from
          thalamus                                              substantia nigra (nuclei) - loss of
                                                                these neurons = Parkinsons
                                                                •red nuclei forms synapses with
                                                                cerebellum to coordinate muscle
                                                                movements
Major Regions and Landmarks
             •   Cerebellum
                 –   divided into hemisphere with lobes - like
                     the cerebrum
                       • anterior and posterior lobes
                 –   involuntary motor activities
                       • evaluates and coordinates motor
                         activities initiated by the cerebrum and
                         corrects problems by sending info back
                         to the cerebrum
                       • regulate posture & balance
                 –   has a superficial layer of gray matter called
                     the cerebellar cortex - like the brain
                 –   deep to the gray matter are tracts of white
                     matter = arbor vitae
                 –   also has nuclei = cerebellar nuclei (origin
                     of neurons that connect the cerebellum to
                     the brain and SC)
                 –   connected to the brain stem by three
                     cerebellar peduncles
                       •   inferior – sensory information from the
                           inner ear and body proprioceptors
                       •   middle – carry commands for voluntary
                           movements that originated into the cortex
                           into the cerebellum for coordination
                       •   superior – connects to the red nuclei and
                           the nuclei of the thalamus
    Medical application: Ataxia
• damage to the cerebellum
• blindfolded people cannot find the tip of
  their nose
• also changed speech patterns due to
  incoordinate speech muscles
• abnormal walking or balance
• alcohol overdose also suppresses the
  activity of the cerebellum
                           The Limbic System
•   called the emotional brain                                 corpus
•   group of structures that surround the brain                callosum
    stem
                                                                       cingulate gyrus
                                                hypothalmic nuclei                 anterior thalmic nuclei
•   involved in olfaction and memory
                                                                                         fornix
•   emotion – anger, fear, happiness…
      – associated with specific responses –
          behavioral patterns
•   basic behavioral patterns
      – -preparing for attack, laughing,
          crying, blushing
      – also includes sexual behaviors for
          the continuation of the species
      – connects with the hypothalamus to
          regulate these behaviors
•   main components:                             olfactory tract
      – 1. limbic lobe: rim of cerebral cortex                                         mamillary body
          on the medial surface of                     amygdala
             each hemisphere – includes the                                      parahippocampal gyrus
                hippocampus (memory)                              hippocampus
      – 2. dentate gyrus
      – 3. amygdala: stimulation - rage
      – 4. olfactory bulbs
      – 5. septal nuclei
      – 6. mammillary bodies of the
          hypothalamus
Medical Application: Alzheimer’s Disease
-loss or reasoning, memory
-11% of population over 65 (4 million people)
-unknown cause – thought to be genetic factors + environmental &
            lifestyle
-neuronal plasma membranes contain a protein = amyloid precursor protein (APP)
            abundant in presynaptic axon terminals
            -cleavage of APP yields a secreted product = sAPPa that is secreted by the
            presynaptic terminals normally
            -if APP is cleaved at the wrong site – beta-amyloid
            -two forms of beta-amyloid are possible based on cleavage site – the longer
            form (Ab40) is harmless
            -but the form Ab42 – 10% of the cleaved b-amyloid – aggregates to form
            plaques and is neurotoxic
-underlying causes for Ab plaque formation remain unknown
-about 15% of cases appear to have a genetic link – familial Alzheimer’s
            -mutations in 3 genes: prenisilin-1, -2 and APP lead to early onset forms
            (less the 15% of all cases) – prenisilins cleave APP
            -mutations in these genes can shift the balance of b-amyloid to the harmful form,
            -so can age
-also mutations in gene coding for apolipoprotein E (ApoE) a protein that helps transport
cholesterol in the blood
            -may account for 85% of the cases – late-onset Alzheimers
            -mutated genes for apoE = apoE4 – may increase risk of development
            -may predispose you to Ab plaque formation, or may hasten the onset - ?????
          Medical Application: Alzheimer’s Disease
  •    -brain abnormalities:
  •          1. loss of ACh releasing neurons from the nucleus basalis (below
  •                     the globus pallidus)
  •          2. beta-amyloid plaques
  •          3. neurofibrillary tangles
  •    -plaque – central core of b-amyloid, surrounded by degenerating nerve endings
        – the plaques attract microglia – inflammatory reaction against the plaque, including the
          secretion of toxic chemicals that harm “bystander” neurons
  •    -tangles – bundles of abnormal filaments that accumulate in the cell
  •          bodies of the affected neurons
        – probably form in response to the formation of Ab plaques – bind to the neurons and alter
        the proper formation of the neurons cytoskeleton – production of tangles
  •    the Ab plaques are also thought to lead to excessive influx of Ca ions which kills the
       cells
        – hippocampal neurons (long-term memory) seem to be vulnerable


  •    -treatments: drugs that inhibit acetylcholinesterase improve alertness by increasing
       Ach signaling in the brain
  •          e.g. Donepezil – only ones currently approved (Aricept)
        – may improve the symptoms – they don’t slow the degeneration


http://en.wikipedia.org/wiki/Alzheimer#Acetylcholinesterase_inhibitors
                                                        I - Olfactory
                                                        II - Optic
                                                        III - Oculomotor
                                                        IV-Trochlear
                                                        V - Trigeminal
                                                        VI - Abducens
                                                        VII - Facial
                                                        VIII - Acoustic
                                                        IX - Glossopharyngeal
                                                        X - Vagus
                                                        XI - Accessory
                                                        XII - Hypoglossal


-cranial nerves – 12 pairs
-considered part of the peripheral nervous system (PNS)
-olfactory & optic contain only sensory axons = sensory nerves
-remaining are either motor or mixed nerves – both motor and sensory axons
“some say my mother bought my brother some bad beer, my my”
                               Spinal Cord
• length in adults = 16 to 18 inches
• Cervical and lumbar
  enlargements
    – cervical = C4 to T1, nerves to and
      from upper limbs
    – lumbar = T9 to T12, nerves to and
      from lower limbs
• Tapers to conus medullaris
• filium terminale arises from the
  CM - extension of the pia mater that
   anchors the SC to the coccyx
• 31 segments each with
    – Dorsal root ganglia
        • Sensory neuron cell bodies
    – Pair of dorsal roots
    – Pair of ventral roots
                       Spinal Meninges
• Specialized membranes
• Provide physical stability and shock absorption
• Three layers
   – Dura mater = dense irregular CT
       • continuous with the brain’s DM
       • above it is the epidural space
   – Arachnoid = continuous with brain
       • above it is the subdural space
       • below is the subarachnoid space
       • avascular
   – Pia mater = connective tissue
       • collagen and elastin bundles
       • well vascularized
• The Pia Mater
     – Innermost meningeal layer
     – Bound firmly to underlying tissue
     – Denticulate ligaments bind pia mater to the arachnoid




-spinal tap: under local anesthetic
-long needle is inserted into the
subarachnoid space and CSF is
withdrawn or antibiotics or
anesthetics are given
-given between L3 & L4 or
L4 & L5
    Histology of the Spinal Cord

• Central gray matter
   – Contains cell bodies of
     neurons and glial cells +
     unmyelinated axons
   – Gray matter projections are
     horns
• Peripheral white matter
   – Myelinated and
     unmyelinated axons
   – Tracts or columns
    Organization of Gray Matter
• Posterior gray horns
   – Somatic and visceral
     sensory nuclei
• Anterior gray horns
   – Somatic motor control
• Lateral gray horns
   – Visceral motor neurons
• Gray commissures
   – Axons of interneurons
     crossing cordated and
     unmyelinated axons
           Organization of White Matter
• Six columns (funiculi)
    – Anterior, lateral and posterior
      white columns
    – Contain tracts
        • Ascending tracts relay
          information from spinal cord
          to brain
        • Descending tracts carry
          information in the opposite
          direction
•   Spinothalamic tract
     –   pain, temperature, deep pressure &
         crude touch
•   Posterior columns
     –   proprioception, discriminative touch,
         two-point discrimination, pressure and
         vibration
•   Direct pathways (corticospinal &
    corticobulbar)
     –   precise, voluntary movements
     –   corticobulbar: cerebral cortex to brain
         stem and out via cranial nerves to
         muscles of head and neck
     –   corticospinal: also called the pyramidal
         tracts (lateral and anterior)
           •   cerebral cortex to spinal cord and out to
               voluntary muscles (synapses with lower
               motor neurons in the ventral gray horn)
•   Indirect pathways (rubrospinal,
    vestibulospinal)
     –   programming automatic movements,
         posture & muscle tone, equilibrium &
         coordination of visual reflexes
     –   rubrospinal: alternate route for
         voluntary movements of arms and legs
           •   red nucleus of midbrain through the
               lateral column
     –   vestibulospinal:

								
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