8/23 Spinal Cord & Spinal Nerves - Glendinning Flashcards Preview

M2 Neuron Brain Behavior > 8/23 Spinal Cord & Spinal Nerves - Glendinning > Flashcards

Flashcards in 8/23 Spinal Cord & Spinal Nerves - Glendinning Deck (24)

spinal nerves


spinal cord

31 pairs of spinal nerves → form part of peripheral nervous system







spinal cord ends approx L1 at conus medullaris

below conus medullaris, find spinal nerves arranged in cauda equina within lumbar cistern (aka inside dural sac)

  • injury below L1? cauda equina lesion


relationship between spinal nerves and vertebral column


C1-C7 exit ABOVE vertebrae

C8 exits below C7 vertebra

all other spinal nerves exit below vertebrae


spinal nerve components and location in spinal cord

dorsal root → dorsal horn : primary sensory afferents

ventral horn → ventral root : "lower" or alpha motor neuron (efferent) to sk muscle

lateral horn (T1-L3) → ventral root

  • lateral horn contains sympathetic preganglionics in intermediolateral nucleus (intermediate nucleus)


parasympathetic nervous system


pregang neurons

arise from cranial nerves (III, VII, IX, X)


also from S2-S4 intermediate zone (intermediomedial nucleus)


distribution of white matter and grey matter at diff levels of spinal cord

more white matter at the top, more grey matter at the bottom


sensory info is coming in at successively higher levels of teh spinal cord

motor is giving off as it goes down






spinal nerves innervate the skin in an orderly, rostral-caudal arrangement

  • touching a segment of skin stimulates/tests a specific dermatome → a specific spinal nerve and spinal cord segment

myotomes are the set of muscles innervated by a single spinal nerve




typical sx

damage to a spinal nerve

most common: herniated disc

also seen: osteophytes, spinal stenosis or foraminal stenosis (hypertrophy of ligamentum flavum or facet)


typical sx:

  • burning, tingling pain that radiates from back along dermatome
    • lancinating or stabbing pain (pay attn to LOCATION)
  • numbness (anesthesia, analgesia)
  • worsening of symptoms with caughing, sneezing, straining
  • muscle weakness
  • **T1 radiculopathy can cause Horner's synrome
    • interrupts sympathetic pathway to eye
      • constricted pupil (miosis)
      • anhidrosis (decr sweating of skin of face)
      • ptosis (drooping) eyelid


external features of the spinal cord

  • dorsal median sulcul
  • dorsal intermediate sulcus
  • dorsalateral sulcus
  • ventral median fissure → LARGE, containing anterior spinal artery


blood supply of spinal cord

anterior spinal artery → 1 in ventral median fissure

  • supplies anterior 2/3 of spinal cord

posterior spinal artery → 2 in posterolateral sulci

  • supplies posterior 1/3 of spinal cord


  • series of branches from anterior and posterior spinal arteries that form a crown around the cord


anterior and posterior radicular arteries arise from segmental arteries at each spinal level to supply roots and ganglia

  • Artery of Adamkiewicz : unusually large ant radicular artery arising from left of T9-L1 → supplies most of lumbar and sacral spinal cord

anterior and posterior spinal medullary arteries arise at intermittent levels (from radicular arteries?) to augment blood supply



radicular arteries supplying the spinal cord


associated clinical issues

cervical radicular artery

thoracic radicular arteries

great radicular artery of Adamkiewicz


clinical issues:

  • T4-T9 watershed area → underperfusion
  • fracture dislocations of vertebra → interfere with blood supply
  • arterial disease obstructing great radicular artery
  • occlusion of aorta during surgery → ischemia


lamina and functional organization of grey matter

spinal cord grey matter is divided into lamina based on cytoarchitecture

10 lamina


I-VI dorsal horn

  • sensory processing

VII intermediate zone

  • sympathetic pregang neurons in intermediolateral cells column (T1-L3)
  • parasympathetic neurons in intermediomedial cell colum (S2-S4)

VIII-IX ventral horn

  • motor neurons and interneurons

X grey matter surrounding central canal


nuclei of spinal cord grey matter and functions

substantia gelatinosa : tip of dorsal horn - pain processing

nucleus proprius : processing of touch

intermediolateral nucleus : 

Clarke's nucleus : processing of proprioception


spinal cord white matter

TRACTS (made up of axons)

long pathways to and from cortex/brainstem

  • interruption of long pathways is why spinal cord injuries lead to major loss of fx BELOW LEVEL OF LESION

short pathways to and from SC segments


3 sections:

  • dorsal funiculus
  • lateral funiculus
  • ventral funiculus


stretch reflex

feedback control of motor neurons

  • stimulus: stretch
  • response: contraction


ex. load increases → biceps/brachioradialis stretch → reflex contraction of biceps/brachioradialis & simultaneous inhibition of triceps


clinical stretch reflex : quadriceps muscle

muscle stretch receptor excited → Ia afferent makes excitatory synapse onto...

  • quadriceps motor neurons → muscle contraction
  • inhibitory interneuron → inhibits hambstring (flexor) motor neurons


location and grading of stretch reflexes

0+ absent

1+ trace

2+ normal

3+ brisk

4+ non sustained clonus

5+ sustained clonus

*1+ 2+, 3+ are generally considered normal UNLESS asymmetry/diff between upper and lower limbs



  • L3-4 patella
  • C5-6 biceps
  • C5-6 brachioradialis
  • C7-8 triceps
  • S1 Achilles


muscle spindles

arranged in parallel with skeletal muscle fibers

proprioceptors : provide information about body position/movement

  • comprised of inftrafusal muscle fibers within a connective tissue capsule


Group IA afferent: respond to rapid stretch (dynamic)

Group II afferent: respond to sustained stretch (tonic)


muscle spindle modulation by gamma motor neurons

gamma motor neurons only innervate muscle spindle intrafusal fibers

  • DONT cause skeletal muscle fibers to contract
  • instead, firing results in increased excitability of the muscle spindle

why do you need gamma motor neurons?

  • when muscle is contracted/shortened, intrafusal spindle fiber is slack
  • gamma fires to get rid of that slack so that the muscle can still be responsive
  • maintain the prioprioceptor feedback of a muscle no matter what the length of the muscle is


therefore...stretch PLUS increased gamma efferent discharge = robust contraction


*extrafusal fiber aka skeletal muscle


normally, alpha and gamma motor neurons are coactivated

  • alpha innervate sk muscle
  • gamma innervate intrafusal 
    • gamma activity increases during skilled movements and motor learning


why is the stretch reflex used clinically?

absent or decreased?  pathology to afferent, efferents, or spinal cord connection

increased? pathology above spinal cord segment



muscle tone

resting tension in a muscle produced by muscle elasticity

  • contributes to postural control, ability to store energy when muscle is stretched (ex. walking, balancing)

hypotonia when spinal nerves are damaged

hypertonia when you get supraspinal lesions because stretch reflexes are increased


Ib inhibitory reflex

stimulus: muscle tension

circuit: Golgi-tendon-organ → Ib afferent → Ib inhibitory interneuron → motor neuron to homonymous muscle

(also hits excitatory interneuron → motor neuron to antagonist muscles)


Golgi tendon organ responds to CONTRACTION (not stretch)




used to think it was for protection BUT turns out mostly active during small movements → helps us achieve more fine, coordinated movements


flexor withdrawal reflex

feedback control to remove a limb from a painful stimulus

ex. if you step on a tack...

  • stimulated leg flexes to withdraw
  • opposite leg extends to support


central pattern generators

used to generate circuits for walking


spinal shock

spinal cord injury → immediate flaccid paralysis

  • loss of all motor and autonomic fx below lesion
    • flaccid paralysis
    • bowel and bladder paralysis
    • loss of vasomotor tone (hypotension)
  • usually 1-6 weeks



loss of descending facilitation that keeps the spinal cord circuits in a continual state of activation/readiness

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