Lecture 6: Lower Motor Neurons Flashcards
Where are alpha lower motor neurons located in the spinal cord?
Ventral horn; Proximal muscles more medial, distal are lateral, flexors are more dorsal to extensors
How are small and large motor neurons matched to muscles?
Small- 1 type muscles fibers that cause slow slowly-fatiguing constractions
Large- IIb fibers that cause large fast quickly fatiguing contractions
Lower motor neuron signs
No reflexes, flaccid paralysis, hypotonia, fasciculations, muscle atrophy
Upper motor neuron signs
Hyperreflexia, spastic paralysis, Hypertonia, + Babinski sign
Corticospinal pathway
Motor cortex to spinal cord tract
Ventromedial pathways
Reticulo, tecto, and vestibulospinal pathways that are involved with proximal/axial muscles
Lateral motor pathways
Corticospinal and rubrospinal; fine movements in distal muscles
What cortex layer do corticospinal fibers arise from?
5
Where do corticospinal neurons cross the midline?
Pyramidal decussation in lower medulla
Where do rubrospinal neurons cross the midline?
Right away in midbrain
Lesion in corticospinal path
In spinal cord- ipsilateral motor deficit
Above spinal cord- contralateral motor deficit
Lesion in rubrospinal path
Contralateral motor deficit no matter where along the length the lesion is
Vestibulospinal path
From ear via CN VIII; ventromedial pathway down to ipsilateral proximal limb and axial muscles to keep balance
Reticulospinal path
Input from motor cortex; descend ipsilaterally to act on alpha and gamma MNs; probably to do with postural adjustment
Tectospinal path
Input from retina to superior colliculus in midbrain; sends input across the midline to muscles that turn head towards stimulus
