descending pathways Flashcards
How many neurons in a descending pathway?
2
Where do lower motor neurons start?
in the ventral grey horn or nuclei in brain stem
name 3 consequences of lower motor neuron lesions?
muscle wasting/ weakness/ absent tendon reflexes
What causes LMN lesions?
injury or poliomyelitis
What are the 2 types of UMN?
corticospinal (cortex to spine, fine motor movement) and corticobulbar (cortex to brainstem)
What are the functions of UMN?
influence LMN activity, modify reflexes, superimpose more complex patterns of movement
How many descending pathways are there and what are they collectively known as?
4, the pyramidal system. other pathways can take over some corticospinal function but fine control lost
Once leaving the precentral gyrus where do UMN fibres pass?
through the internal capsule- fibres to body through posterior limb, fibres to face through genu
Where do the fibres of UMN run after leaving the internal capsule
cerebral peduncles, pons, then pyramids
Where do UMN fibres dessucate?
in the pyramids (aprox 85% fibres)
Where do the UMN fibres descend after dessucation?
lateral corticospinal tract
Where do the UMNs that descend ipsilaterally descend?
the anterior corticospinal tract, cross to ventral gery horn via ventral white commisure
Where do all UMNs contact cell bodies of LMNs?
contralateral ventral grey horn
Innervation of LMNs in the face is bilateral except..
hypoglossal- only served by contralateral hemisphere, facial- Upper face bilateral but lower face only contralateral
Where are the nuclei located?
floor of the 4th ventricle?
