Descending pathways Flashcards
where do upper motor neurones originate
1st order neurones in the cerebrum and the subcortical structures
where do lower motor ebonies originate from
originate and have their cell bodies in the brain stem and spinal cord (ventral grey horn)
what are the three descending pathways
corticospinal - from cortex to spinal cord which initiates movement - body muscles
corticonucelar - from cortex to brainstem - control facial muscles and initiate movement
extrapyramidal - 3 different tracts which modify and coordinate movement
what is the general route of the corticospinal/nucelar pathway
cerebral cortex to precentral gyrus to internal capsule to brainstem / spinal cord
what is the nerve difference between the corticonucelar and spinal tracts
nuclear - cranial nerves
spinal - spinal nerves
what are the locations of the descending fibres in the midbrain, pons and medulla
midbrain - cerebral peduncles (crus cerebri)
pons - ventral pons as fascicles
medulla - pyramids
which of the nucelar/spinal descending pathways cross the midline
corticospinal decussate at the pyramids but corticonucelar does not
what are the 6 steps in the corticospianl tract
cerebral cortex internal capsule crus cerebrii ventral pons open medulla (rostral pyramids) crossing at the decussation of pyramids in the closed medulla
what happens to the cortospianl tract after the decussation of pyramids and what does this mean
85% fibres cross and enter the lateral corticospinal tract (contralateral)
15% don’t cross and enter the anterior corticospinal tract (ipsilateral)
bilateral innervation
what is the somatotropin organisation of the lateral corticospinal tract and what is its role
neurones for the leg are lateral and for the arm medial
leave through ventral grey horn for limb musculature
attach to lower motor neurones on the same side
what is the role of the anterior corticospinal tract
contact lower motor on both sides (both ventral grey horns) for axial musculature (bilateral innervation)
what is the main method of innervation of LMN’s for the corticonucelar pathway and give an example
bilateral except for the lower facial and extrinsic tongue muscles which are under contralateral control
hypoglossal nerve = contralateral central
what is the corticonucelar input to facial motor nuclei
bilateral input to facial nucelli in the pons via internal capsule
upper face = LMN’s from both nuclei
lower face LMNs from the ipsilateral facial nuclei which receives input fromm the centrallatersal cortex
how can lower motor neurone damage occur and where does it occur
injury to ventral grey horn or axon as it leaves the spinal cord
may be due to poliomyelitis - acute viral infection of neurone - muscle wasting
what would an LMN lesion of descending motor pathway cause at the level of the lesion
hyporeflexia or areflexia
muscle wasting, weakness hypotonia
