5- motor tracts Flashcards
what is the internal capsule
bidirectional white matter pathway containing descending motor fibres of UMN and ascending axons of 3* sensory neurones
what is in the anterior limb of the internal capsule
axons connecting the motor cortex with the cerebellum
what is in the genu of the internal capsule
contains axons of the upper motor neurones supplying the face
what is in the posterior limb of the internal capsule
axons of motor neurones supplying upper limb, trunk and lower. also 1/3 of sensory axons connecting thalamus to post central gyrus
what does the lateral CST and the ventral CST supply
lateral- distal muscles
ventral- proximal and trunk
describe the destinations of axons past the medullary pyramids
85% decussate to form lateral CST
15% remain ipsilateral and descend in the ventral funicular as the ventral cst. descussate at level of target LMN
where are the cell bodies of UMN and LMN located
upper- primary motor cortex, pre-central gyrus, frontal lobe
lower- most in ventral horn of spinal cord, some in brainstem
where are LMN not found
basal ganglia/cerebellum
describe the neurones involved in a reflex arc
afferent from spindle fibres in patellar ligament synapses onto the lower motor neurone to cause contraction of quadriceps. the sensory neurone also sends descending fibres down spinal cord which synapse onto inhibitory inter-neurones to prevent hamstring contraction. modulated by descending pathways.
describe the effect of stroke on reflexes
can damage modulatory fibres, causing unusual reflexes
where are upper and lower limb fibres located in the CST compared to in motor homunculus
CST- upper- medially, lower- laterally
homunculus- upper lateral , lower medial
describe the innervation of the trigeminal, facial and ambiguous nuclei and the effect of stroke on them
- trigeminal, upper facial and nucleus ambiguous have bilateral and so are less affected by stroke. swallowing muscles/ mastication/forehead spared
- lower facial has unilateral and so is affected by stroke
what do thalamic radiations contain
tertiaryy ascending sensory fibres
describe how spasticity occurs in UMN lesion
- cortical lesion such as stroke destroys CST and descending inhibitory neurones
- LMN enters spinal shock
- still has muscle spindle and so has excitatory inputs, however has lost all inhibitory inputs from the descending inhibitory pathway
- causes increase in activity, action potentials and muscle contraction
why does spasticity cause flexion not extension
although both muscle groups have equal loss of innervation, the flexors are more powerful muscle groups
