Flashcards in Spinal reflexes, upper motor neurones and control of movement Deck (36)
What do spinal interneurons receive input from?
Primary sensory axons
Descending axons from the brain
What are the different types of input that can be given to a spinal interneurons?
What do inhibitory interneurons mediate?
Inverse myotatic response
What is reciprocal inhibition?
Reflex results in contraction of extensor muscle whilst simultaneously relaxing the antagonist flexor muscle
Describe the pathway for reciprocal inhibtion
1a afferent from muscle spindle extensor makes an excitatory monosynaptic contact with alpha motor neuron innervating the homonymous muscle
Via polysynaptic pathway involving an inhibitory interneuron, the 1a fibre also inhibits the alpha motor neurone supplying the flexor muscle
What will excitatory interneurons mediate?
Crossed extensor reflex
What is the flexor reflex?
Noxious stimulus causes the limb to flex by:
Contraction of flexor muscles via excitatory interneurons
Relaxation of extensor muscle via excitatory and inhibitor internueons
What is the crossed extensor reflex?
Noxious stimulus causes the limb to extend via:
Contraction of extensor muscles via excitatory interneurons
Relaxation of flexor muscles via excitatory and inhibitory interneurons
What does the crossed extensor reflex enhance?
Postural support during withdrawal of a foot from a painful stimulus
What are the descending spinal tracts concerned with?
Control of movement
Spinal autonomic functions
Modulation of sensory transmission
Describe the lateral descending pathways
Under control from the cerebral cortex
Important for voluntary control of distal musculature
Describe the ventromedial pathways
Under control from brain stem
Important for posture and locomotion
Which pathways make up the lateral pathways?
Which pathways makeup the ventromedial pathways?
Lateral vestibulospinal tract
Ventral corticospinal tract
Where do axons in the corticospinal tract decussate?
85% at medullary pyramids to form the lateral corticospinal tract
Remainder stay ipsilateral to form the ventral corticospinal tract to decussate more caudally
Where will axons of the corticospinal tract terminate?
Dorsolateral region of ventral horn of grey matter
Location of LMNs and interneurons controlling distal muscle particular flexors
Where are the cell bodies of the rubrospinal tract found?
Red nucleus - receives input from the motor cortex and cerebellum
Where will axons of the rubrospinal tract decussate?
Ventral tegmental decussation and descend the spinal cord ventrolateral to the lateral corticospinal tract terminating at the ventral horn
What is the function of the rubrospinal tract?
Exerts control over limb flexor muscles exciting LMNs of those muscles
What are lesions of the lateral columns associated with?
Loss of fractionated movements
Slowing and impairment of accuracy of voluntary movements
Little effect on posture
Where are cell bodies of the vestibulospinal tracts found?
Where will the vestibular nuclei receive input?
Where will axons from the lateral vestibular nucleus descend?
Ipsilaterally as the lateral vestibulospinal tract as far as the lumbar spinal cord
What is the function of the lateral vestibulospinal tract?
Balanced posture by facilitating extensor MNs of antigravity muscles
Where will axons from the medial vestibular nucleus descend?
Medial vestibulospinal tract as far as the cervical spinal cord
What is the function of the medial vestibulospinal tract?
Activates cervical spinal circuits that control neck and back muscles guiding head movement
Where do the cell bodies from the tectospinal tract reside?
What input does the tectospinal tract receive?
Afferents conveying somatosensory and auditory info
Where will axons from the tectospinal tract run?
Decussate in dorsal tegmental decussation
Descend close to the midline to the cervical spinal cord