1. this is H shaped with the central canal running thru the middle

 2. the gray contains dorsal & ventral horns and an intermediate area
   A. lateral horn:

 3. there are 3 main categories of neurons in the gray
   A. interneurons: these are the smallest

   B. motor neurons: in the ventral horn that supply skeletal muscle
     a. they consist of alpha & gamma motor neurons

   C. tract cells: cell bodies with axons that make up ascending fasciculi

 4. Laminae of Rexed: similar groups of neuronal cell bodies occur in long
    columns thru out the length of the cord

   A. laminae I – VI receive afferent axons
   B. autonomic motor neurons in laminae VII
   C. motor interneurons in laminae VIII for motor reflexes
   D. motor neurons mostly in laminae IX
   E. cells in laminae X surround the central canal (visceral pain perception)
 

II. white matter

 1. it consists of 3 funiculi (Kingsley p.168)
  A. dorsal funiculus (dorsal columns): consist of two sensory tracts
    a. gracile fasciculus (GF)
    b. cuneate fasciculus (CF): only in the cervical & upper thoracic cord
 
  B. lateral funiculus (lateral white columns)

  C. ventral funiculus (ventral white columns)
    a. anterior lateral system:

 2. ventral white commissure: axons cross here

 3. dorsolateral tract (of Lissauer):
 
 

I. dorsal column pathway (medial lemniscus system): This is a 3 neuron pathway.  This pathway carries discriminative touch & proprioceptive information  Kingsley p. 181

  1. first order neurons: these are the somatosensory receptors (neurons)

    A. cell bodies in the dorsal root ganglia & cranial nerve ganglia.
      a. somaosensory cranial nerves include: trigeminal (V), facial (VII),
          glossopharyngeal (IX), & the vagus (X).   (Kingsley p. 183)

    B. some synapse in the gray matter at their own segmental level

    C. some primary neuron fibers ascend (via GF & CF) & synapse in their
         corresponding nucleus (i.e., gracile & cuneate nuclei in the medulla)
 

  2. second order neurons: axons from these neurons ascend to thalamus
    A. cell bodies in the gracile & cuneate nuclei

    B. secondary neuron axons then decussate (cross the midline)
      a. internal arcuate fibers

    C. fobers synapse in the ventral posterior nucleus of the (thalamus)
      a. ventral posterior nucleus (VP): (Kingsley p.175)

  3. third order neurons: axons ascend to the somatosensory cortex

    A. cell bodies in the ventral posterior nucleus of the thalamus

    B. the fibers ascend to & synapse in the postcentral gyrus

    C. there are maps of the body on the somatosensory cortex (Kingsley p.
         185)
 

II. anterolateral columns: this system carries pain & temperature information (Kingsley p. 189)

 1. first order neurons: these are the somatosensory receptors
   A. upon entering the cord they soon synpase in the dorsal horn

 2. second order neurons: axons from neurons in Laminae IV,V, & IV (nucleus
     proprius) immediately decussate & ascend
   A. axons cross in the ventral white commissure & ascend

   B. many synapse in the brainstem, cerebellum, hypothalamus, or limbic
        system

   C. some second order axons synapse in the thalamus (spinothalamic tract).
        Kingsley p. 175 for thalamic areas
      a. intralaminar nuclei
      b. ventral posterior nucleus

 3. third order neurons: cell bodies in the thalamus
    A. axons ascend to the somatosensory cortex
 

I. two types of pain

  1. physiological pain: results from stimulation of nociceptors
    A. two  types of receptors are important
      a. stimulation of  A-delta fibers results in sharp localized pain

      b. stimulation of C fibers results in dull burning or aching pain which
          lingers after the stimulus is removed

  2. neuropathic (intractable) pain: pain that shows no useful function
   A. due to injury of the nervous system

   B. allodynia: is one example, previously nonpainful stimuli elicit pain

   C. often observed after amputation (phantom pain)

   D. entrapment syndrome: peripheral nerves become irritated & inflamed
     a. for example a bone can press on a nerve
       -ulnar nerve in the elbow (funny bone)
       -median nerve in the carpal tunnel of the wrist (carpal tunnel synd).

   E. CNS damage can also result in neuropathic pain
     a. most likely to occur after damage to the ventral posterior nucleus
 

II. Sensitization two types

 1. peripheral sensitization: (p. 152, 154, & 190 of Kingsley)

 2. central sensitization: physiological pain can cause changes in spinal cord-
    projection neurons that make the pain more intense
 

III. gate control theory: the transmission of painful information can be
inhibited by stimulation of mechanoreceptors (i.e., tactile stimulation) (Kingsley p. 192)
 
  1. how might this work?
    A. stimulation of non-nociceptive receptors causes excitation of inhibitory
         Interneurons which causes suppression of C pain fibers by way of
         presynaptic inhibition (i.e., it closes the pain gate)

  2. transcutaneous electrical neural stimulation (TENS):
 

IV. descending pain pathways: (Kingsley p 193)

  1. endogenous opioid systems have been implicated
    A. opiates inhibit the activity of inhibitory interneurons in the
         periaqueductal gray (PAG) causing excitation of descending axons
    B. the activity of axons descending form the PAG excite cells in the raphe
         nucleus
    C. the activity of descending axons from the raphe nucleus excites
         inhibitory interneurons in the spinal cord
    D. excitation of inhibitory interneurons inhibits neurons that send ascending
         pain messages to the brain (i.e., C fibers)
 

V. surgical procedures for pain

  1. cutting dorsal root fibers or anterolateral system (ALS) fibers

  2. lesions of the ventral posterior nucleus of the thalamus (where ALS
      synapses)

  3. lesions of areas of the cerebral cortex have also been attempted
 

VI. Damage to peripheral axons

 1. complete cuts of spinal or peripheral nerves results in losses in sensory &
    motor abilities
  A. sensory & motor axons travel together in nerves

 2. damage to a single dorsal root would cause you to lose sensory abilities in
    its corrsponding dermatome (Kingsley p. 196)
  A. dermatome: the area of skin supplied by axons from a single dorsal root
  B. cutaneous areas supplied by adjacent dorsal roots overlap

 3. damage to peripheral nerves would likely cause sensory loss in parts of
    more than one dermatone (Kingsley p. 198)

 4. peripheral neuropathy: degeneration in peripheral nerves that cause
    sensory loss & muscle weakness.
  A. this condition often effects long axons first so symptoms often start in
       the extremities (stocking & glove pattern) Kingsley p.199

 5. referred pain: visceral pain is often perceived as arising from surface areas
    see Kingsley page 200
 

VII. Damage to central neurons

 1. your likely to see dissociations of functions: e.g., sensory abilities affected
     but motor abilities in tact or visa versa
  A. spinal cord hemisection results in sensory dissociations (e.g., Brown-
       Sequard syndrome; Kingsley p. 199)
 

 2. brainstem or cerebral cortex lesions usually produce a deficit in all
     somatosensory modalities on the contralateral side of the body (Kingsley
     p. 199)

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