Spinal Cord The Spinal Cord Basic Neuroscience by MikeJenny


									The Spinal Cord

       Basic Neuroscience

      James H. Baños, Ph.D.
Grey and White
     Grey and White Matter

Grey Matter = Cell Body

                 White Matter = Myelinated axon
        Grey and White Matter
   Grey matter
     Cortex
     Nucleus (CNS)

     Ganglion (PNS) Exception: Basal Ganglia
           Grey and White Matter
   White Matter
       Nerve (PNS)
       Tract (CNS)
       Fasciculus/Funiculus -- Group of fibers with common origin and
       Lemniscus -- Ribbon-like fiber tract
       Peduncle -- Massive group of fibers -- usually several tracts
          Grey and White Matter
   Tracts are named with origin first, then
       Corticospinal tract -- cortex to spinal cord
       Mammilothalamic tract -- Mammilary bodies to
       Spinocerebellar tract -- Spinal cord to cerebellum
       Corticobulbar tract -- Cortex to brain stem
The Spinal Cord
                  General Organization

   Spinal cord is SMALL!
       42-45 cm long
       1 CM wide at widest point
       Does not extend all the way to the bottom of the spinal column
   Pattern of grey/white matter is reversed in the cord
       White matter tracts on outside
       Grey matter on the inside
       Staining reverses this!!!
General Organization

                  White matter (tracts
                  of axons)

                  Grey Matter
                  (cell bodies)
                 General Organization

   Spinal cord is segmented anatomically
   Input and output occurs in groups of rootlets
    arranged in a series longitudinally along the cord
       Dorsal rootlets -- Input -- carry sensory information
       Ventral rootlets -- Output -- motor neurons
            General Organization

   Each set of rootlets forms a spinal nerve
    that innervates a corresponding segment
    of the body, called a dermatome
General Organization
             General Organization

   There are 31 segments in the spinal cord:
     8 cervical (C1 - C8)
     12 Thoracic (T1 - T12)

     5 Lumbar (L1 - L5)

     5 Sacral (S1 - S5)

     1 Coccygeal
             General Organization

   The spinal cord is housed within the
    vertebral column
General Organization

            Each cord segment has a
             corresponding vertebra of
             the same name (e.g., C3)
            Spinal nerves enter/exit
             underneath their
             corresponding vertebral
             General Organization

   But wait! Something doesn’t add up!
     How can spinal nerves exit below their
      corresponding vertebral segment if the cord is
      only 42cm-45cm long?
     Answer: Spinal nerves extend down to the
      appropriate vertebral segment forming the
      cauda equina
   This means cord segments and vertebral
    segments don’t line up
General Organization
             General Organization

   Cord is not of uniform thickness
    throughout its length. Why not?
              General Organization

   Cord is not of uniform thickness
    throughout its length. Why not?

   Answer:
     Segments of the cord innervate parts of the
      body that differ in complexity
     There are fewer white matter tracts lower in
      the cord.
General Organization

             Cervical enlargement
             C5 - T1

             Lumbar enlargement
             L2 - S3
The Spinal Cord in
  Cross Section
                Cord Sections

   Segments of the spinal cord have a similar
    organization, but vary in appearance.
   Always know where you are in the cord
    (i.e., cervical, thoracic, lumbar, sacral)
Cord Sections -- Cervical

               Cervical cord is wide,
                flat, almost oval in
                appearance. Why?
Cord Sections -- Cervical Enlargement

                    What’s different about
                     the cervical
                     enlargement . Why?


              Cervical Enlargement
Cord Section -- Thoracic

               Less White matter
                than cervical
               Rounder appearance
               Less prominent
                ventral horns than
                cervical enlargement
  Cord Section -- Lumbar

                        Less White matter
                         than thoracic
                        Rounder appearance
                        Larger ventral horns,
                         especially in lumbar

Lumbar Enlargement
Cord Section -- Sacral

              Not much white
              Mostly grey, although
               not much of that
             Cross Sectional Organization
 Posterior intermediate sulcus            Posterior median sulcus

Tract of

                                            Anterior white commisure
                             Anterior median fissure
Grey Matter

             Laminar
                 Laminae of
Grey Matter

             Posterior (dorsal)
             Intermediate Grey
             Anterior (ventral)
Grey Matter: Posterior Horn

                     Mostly Interneurons
                         Substantia gelatinosa
                              Pain/temp proc

                         Body of the posterior
                              Sensory proc
Grey Matter: Intermediate Grey

                       Clarke’s Column
                           T1-L3
                           Balance/proprio.
                       Intermediolateral
                           T1-L3
                           Sympathetic neurons
Grey Matter: Anterior Horn

                     Lower Motor
White Matter: The “Big Four” Pathways

                          Corticospinal tract
                          Dorsal Columns

                          Spinothalamic tract

                          Spinocerebellar tracts
                    The Big Four
   Corticospinal tract
       Voluntary motor

   Dorsal columns/ medial lemniscus
       Discriminative touch
       Conscious proprioception

   Spinocerebellar tract (dorsal and ventral)
       Unconscious proprioception

   Spinothalamic tract
      Pain/temperature
Corticospinal Tract
     Voluntary Motor
                     Corticospinal Tract

   First order neuron (upper motor neuron) originates in
    precentral gyrus
   Passes through internal capsule
   90% decussates in caudal medulla
       Lateral corticospinal tract
   10% undecussated
       Anterior corticospinal tract
   Synapses on second order neuron (lower motor neuron)
    in ventral gray of the cord
   Second order neuron innervates muscle
Motor Homunculus

              Motor Homonculus

       Arms           Legs

              Corticospinal Tract

Spinal Cord
                 Medulla   Pons   Midbrain
            Upper & Lower Motor Neurons
                      Upper Motor Neuron
Motor Ctx
                          Motor Cortex to Ventral Grey Horn
                          Modulatory influence on stretch reflex arc

    UMN               Lower Motor Neuron
                          Ventral Grey Horn to Neuromuscular Junction
                          Efferent of stretch reflex arc
Ventral                   Helps maintain tone
Grey Horn             Sensory Neuron
                          Stretch receptors in muscle and tendons
                          Helps maintain tone
    LMN                   Afferent of basic stretch reflex arc
      Upper & Lower Motor Neurons
                Maintenance of Tone
                  Input from stretch receptors causes
                   lower motor neuron to supply tonic
UMN                stimulation to the muscle
                  The upper motor neuron modulates
                   this -- will tend to “override” the
                   tonic signal from the sensory
      Upper & Lower Motor Neurons
                Reflex Arc
                   Afferent is sensory neuron
                    detecting a sudden stretch
                   Signal is strong and results in a
                    strong response by the lower motor
                   Strong signal usually overcomes
                    mild cortical input from the UMN
            Upper & Lower Motor Neurons
                      Upper Motor Neuron Signs
Motor Ctx
                          Spastic paresis
                          Hypertonia
                          Hyperreflexia
                          No muscle atrophy (until perhaps late in the
                          Positive Babinski
Grey Horn             Why?
                          Loss of voluntary UMN signal
                          Loss of modulation of tone and reflexes by
    LMN                    UMN -- the circuit runs unchecked
            Upper & Lower Motor Neurons
                      Lower Motor Neuron Signs
Motor Ctx
                          Flaccid paresis/paralysis
                          Muscle fasciculations
                          Hypotonia
                          Hyporeflexia
                          Muscle atrophy
Ventral                   Negative Babinski
Grey Horn             Why?
                          Loss of LMN for voluntary movement
                          Loss of efferent component of reflex arc and
    LMN                    tone pathway
              Babinski’s Sign
   In response to stimulation of the sole of the foot,
    the toes will usually curl downward.
   When UMN inhibition is removed, the toes will
    curl upward (Dorsiflexion). This is referred to as
    a positive Babinski or presence of Babinski’s
            Related Terms…
   Spasticity -- Increased muscle tone and
    increased reflex contraction (UMN)

   Clonus -- Rythmic contractions and
    relaxations seen when a spastic muscle is
    stretched (UMN)
            Basics of Localization

   If all limbs are checked for upper and
    lower motor neuron signs, you can begin
    to localize lesions
   Left-right differences are also very
 Dorsal Column/
Medial Lemniscus
    Discriminative Touch
  Conscious Proprioception
      Dorsal Columns/Medial Lemniscus

   First order neuron begins in receptor
   Enters cord at tract of Lissauer
   Legs run in fasciculus gracilis (medial dorsal)
   Arms run in fasciculus cuneatus (lateral dorsal)
   Synapse on nucleus gracilis and nucleus cuneatus
    (caudal medulla)
   2nd order neuron decussates and runs from NG & NC to
    thalamus (as medial lemniscus)
   3rd order neuron runs from thalamus to postcentral
      Dorsal Columns/Medial Lemniscus

Spinal Cord
               Medulla   Pons   Midbrain
Spinocerebellar Tracts

   Unconscious Proprioception
    Dorsal (Posterior) Spinocerebellar Tract
   Involves Clark’s Column, a longitudinal gray matter body
    from about T1 to L3
   Below Clark’s Column:
        Runs with f. cuneatus, synapses in Clark’s Column, joins dorsal
         spinocerebellar tract
   Level of Clark’s Column
        Synapses in Clark’s Column, joins dorsal spinocerebellar tract
   Above Clark’s Column
        Runs with f. cuneatus, synapses in lateral cuneate nucleus
         (caudal medulla), projects to ipsilateral cerebellum
Dorsal (Posterior) Spinocerebellar Tract

L3            T1

Spinal Cord
                   Medulla       Pons   Midbrain

                        To Cerebellum
Ventral (Anterior) Spinocerebellar Tract
   Supplements Dorsal Spinocerebellar Tract
   Information from more diverse array or receptors
   Originates from scattered cells in the
    intermediate grey caudal to L1 (which in turn
    have input from proprioceptive axons or their
   Crosses twice, to end up in ipsilateral
Ventral (Anterior) Spinocerebellar Tract

Spinal Cord
              Medulla   Pons   Midbrain
Spinothalamic Tract
    Pain and Temperature
                 Spinothalamic Tract

   First order neurons originate in pain receptors, enter
    cord at tract of Lissauer, and synapse in substantia
    gelatinosa or nucleus proprius
   Second order neurons cross at the anterior white
    commissure, rising 1 or 2 cord levels in the process, and
    form contralateral spinothalamic tract
   A third order neuron (not technically spinothalamic tract)
    projects to the cortex
Spinothalamic Tract
              Spinothalamic Tract

Spinal Cord
                 Medulla   Pons   Midbrain
L1   L1

L2   L2

L3   L3

L4   L4
L5   L5
             Coming Up…
   Lab Week Overview: Monday
   Virtual Labs
   Wet lab day: Thursday
   Lab Practical Exam: Friday

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