Download Changes in spinal cord

Spinal cord motor & sensory
Spinal
nerves
-31 pairs  8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
-C1 & C2 exception to rule below  they are not mixed, one is principally motor the other sensory
*Dorsal roots  sensory; cell bodies live in dorsal root ganglia
*Ventral roots  motor; cell bodies live in gray matter of ventral horn (cell bodies actually in
spinal cord itself)
Spinal
vasculature
-arteries arise from 2 sources  vertebral arteries & radicular arteries
-vertebral arteries
*give off branches in upper cervical region that will give rise to 3 spinal arteries  1 anterior & 2
posterior
*these arteries course the entire length of the spinal cord
-radicular arteries
*arise from regional arteries, such as the posterior intercostal & lumbar branches of the
descending aorta
*feed into the longitudinal arteries at various points along the spinal cord
-all these arteries do not supply enough blood to keep cord alive  if you accidently clip a small
artery, you can kill off a large portion of spinal cord
*takes a ton of blood to keep it alive!
-venous drainage  numerous veins – longitudinal veins anterior & posterior to cord
*connect to veins paralleling the dorsal & ventral roots
*drain into internal vertebral plexus found in epidural fat
Spinal
sensory
pathways
-5 separate modalities of sensation  proprioception & touch (mechanical senses) and
temperature, pain, itch (“protective” senses)
*different pathways in the spinal cord
-different sensory modalities end the cord in different areas  all still enter via dorsal root but at
different spots
*this is b/c spinal cord is laminar & it has a somatotopic organization  clinically, this makes it
easier to figure out where lesions are located on the spinal cord; but takes very little damage to
take out a large region of sensory/motor
-sensory homunculus of the parietal cortex (postcentral gyrus)
Mechanical
senses
-touch  mechanoreceptors; Pacinian corpuscles; myelinated A-beta fibers
-proprioception  mechanoreceptors; myelinated A-alpha & -beta fibers
*joints help you realize where you are/where muscles are
-dorsal column – medial lemniscus pathway (back of spinal column)
-primary neuron in DRG receiving information
-first synapse in brain stem  dorsal column nucleus
-receptors in peripheral tissue  input to soma in DRG; enter cord via dorsal horn; ascend in dorsal
columns; synapse in nuclei of dorsal column
-secondary neurons “decussate” or cross midline to opposite side of CNS
Protective
senses
-temperature  thermoreceptors; myelinated A-delta & unmyelinated C fibers
-pain  nociceptors; myelinated A-delta fibers (fast) & unmyelinated C fibers (slow)
-itch  histamine; unmyelinated C fibers
-anterolateral pathway
-primary neuron in DRG
-first synapse in dorsal horn of spinal cord at level it enters
-receptors in peripheral tissue (bare nerve endings)  input to soma in DRG; enter cord via dorsal
horn; SYNAPSE at or near level of entry to dorsal horn; secondary neurons in dorsal horn
-“decussate” via ventral commissure in spinal cord
*MOST NEURONS DECUSSATE AFTER FIRST SYNPASE NO MATTER WHERE LOCATED!
-ascend in anterolateral columns
Sensory
lesions
-cut spinal cord on L, L4  going to lose protective sensation on R lower side; lose L mechanical
senses from that point down
-Brown-Sequard Syndrome
Spinal
motor
pathways
-originate from 2 regions of CNS  cortical (frontal lobe, premotor & motor cortex, precentral
gyrus) & brain stem motor nuclei
*cortical (voluntary movements mainly)  lateral corticospinal tract; ventral corticospinaltract;
corticobulbar tract
*brain stem (nonvoluntary movements & coordinated movements mainly) rubrospinal tract;
reticulospinal tract; tectospinal tract; vestibulospinal tract (orienting self in space)
MOTOR INPUTS
-Brain stem nuclei - Mainly “automatic” stuff
-Primary motor cortex - Mainly voluntary movements
-Basal Ganglia and Cerebellum - Fine tuning, automatic actions
*No direct input to spinal motor neurons
-Secondary motor neurons and interneurons - Directly affect muscles; axons travel to PNS as the
motor portion of spinal nerves
*interneurons – linked sensory & motor neurons  gives you reflexes
-motor portion of spinal cord is somatotopicaly organized (precentral gyrus)
-motor homunculus
Motor
tracts
-two separate pathways
*lateral columns (black circle); usu. contralateral; decussate in brainstem
*ventral columns (red circle); usu. ipsilateral; decussate in spinal cord
CORTICOSPINAL TRACTS
-lateral
*frontal cortex to ventral horn neurons
*decussates in pyramids – junction of medulla & cord
*primary motor pathway for most muscles
*contralateral in cord
-ventral
*primary motor cortex to ventral horn of cervical & upper thoracic region only!
*ipsilateral in cord until it reaches terminal level – many fibers decussate in ventral commissure –
bilateral motor function
-corticobulbar
*terminated primarily in motor nuclei in pons & medulla
*principally associated with cranial nerve motor function
-rubrospinal  red nucleus to ventral horn of cervical spine ONLY; decussates in midbrain
-reticulospinal
*from reticular regions of pons & medulla to ventral horn
*descend in ipsilateral cord; but exert bilateral motor control
*branches or interneurons at terminal level
*mainly function to control “automatic functions” such as walking or posture
-tectospinal
*from superior colliculus to ventral horn of cervical region
*decussates at level of colliculus
*only functions in upper limb/neck
*tectum is associated with visual movements also- coordination of muscle with visual input?
Changes in
spinal cord
-vestibulospinal
*coordinate head & eye movements
*two separate nuclei  lateral – balance (ipsilateral path, but interneurons decussate); medial –
head/neck position (bilateral path)
-spinal cord varies in diameter depending on what region you observe
*cervical & lumbar portions are larger, & have much larger ventral horns  d/t presence of motor
neurons for limbs
Motor
nerve
damage
-damage to lateral tracts tends to lead to loss of function from level of damage down-contralateral
(b/c decussate at level enter spinal cord)
*leads to initial flaccid paralysis
*later patients will develop spastic paralysis & inappropriate reflexes
-damage to ventral tracts does not usu. present as severely, have some loss of function from level
of damage down- ipsilateral AND contralateral
*why does this not have as much effect as lateral tract damage?  b/c some decussate & some
do not on either side!