Descending tracts in spinal cord Flashcards
corticospinal tract
where does it originate
main tract for nearly all voluntary muscle activity
originates in precentral gyrus of frontal lobe (Brodmann’s area 4) `
other name for corticospinal tract
because many of the cell bodies have pyramidal shape
also because it decussates in the pyramids in the medulla oblongata
where are the cell bodies of neurons that motor supply
foot and leg muscles:
head and face muscles:
foot and leg muscles: medial aspect of the precentral gyrus
head and face muscles: lateral aspect of the precentral gyrus
route through the brain of the corticospinal tract
cell bodies in the cortex
axons pass through internal capsule
pass down into cerebral peduncles in the midbrain
continues down the brainstem to the pyramids of the medulla oblongata
majority cross in the pyramidal decussation
become lateral corticospinal tract
route of the lateral corticospinal tract
at each level of the cord axons peel off and enter the ventral horn
terminate by synapsing with lower motor neurons
corticospinal tract axons that do not cross over medulla
minority
continue down on the same side to enter white columns of spinal cord
most will cross lower down
known as ventral corticospinal tract
ventral corticospinal tract
axons peel off and cross over to other side at each level of the spinal cord
enter the ventral horn and terminate on lower motor neurons
corticospinal fibres that do not cross anywhere
3%
end in synapses ipsilateral side as motor cortex
upper motor neurons of corticospinal tracts
route
single uninterrupted neuron
synapse on lower motor neurons in the ventral horn
lower motor neurons
route
send their axons out of spinal cord via ventral roots
branch out in peripheral nerves to voluntary muscles `
suppressor part of the pyramidal tract
fibres that do not initiate impulses to voluntary muscles
prevent lower motor neurons from over discharging
effect of damage to suppressor fibres of corticospinal tract
lower motor neurons are freed from control and fire excessively
in response to reflex stimuli or discharge spontaneously
rubrospinal tract route
what muscles does it supply
from red nucleus in the midbrain to lower motor neurons in the cervical part of the spinal cord
for upper limb muscles
vestibulospinal tract route
what muscles does it supply
from vestibular nuclei to lower motor neurons in spinal cord
for axial musculature
reticulospinal tract route
what muscles does it supply
from brain reticular formation to lower motor neurons in the spinal cord
axial musculature
where do upper motor lesions occur
anywhere along corticospinal tract
from cell bodies in cerebral cortex
descending axons in the internal capsule, brain stem and spinal cord
most common injury site and cause of upper motor lesions
cerebral hemisphere before pyramidal decussation
most often results from artery occlusion and deprived blood supply
if upper motor lesion is above pyramidal decussation, where will signs be seen
muscles on the opposite side of the body
why can a person who is paralysed on one side of the body make crude movements of the trunk musculature on that side
3% of corticospinal fibres do not cross over and they supply the muscles
regaining some lost functions after a stroke
involves cortical plasticity
neurons can take on new functions with training and therapy
effect of upper motor neurons on:
reflexes
suppressor part of tract
lower motor neurons
reflexes: not affected
suppressor part of tract: no longer effective
lower motor neurons: over discharge and fire spontaneously
upper motor neuron paralysis
spasticity
Babinski reflex can be elicited
Babinski reflex
when the sole of the foot is stroked in a heel to toe direction the toes bend upwards
when patients have upper motor neuron lesion
healthy patients toes curl downward
lower motor neuron lesion
occurs when cell bodies of the ventral horn are selectively destroyed or when a nerve is cut
muscles are deprived of nerve supply
muscle paralysis in lower motor lesion
unable to contract
become soft, atrophic and flaccid
reflexes in lower motor lesions
muscles cannot respond to sensory stimuli
