Spinal reflexes, upper motor neurones and control of movement

Question 1

What do spinal interneurons receive input from?

Answer 1

Primary sensory axons
Descending axons from the brain
Collateral LMNs
Other interneurons

Question 2

What are the different types of input that can be given to a spinal interneurons?

Answer 2

Excitatory

Inhibitory

Question 3

What do inhibitory interneurons mediate?

Answer 3

Inverse myotatic response

Reciprocal inhibition

Question 4

What is reciprocal inhibition?

Answer 4

Reflex results in contraction of extensor muscle whilst simultaneously relaxing the antagonist flexor muscle

Question 5

Describe the pathway for reciprocal inhibtion

Answer 5

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

Question 6

What will excitatory interneurons mediate?

Answer 6

Flexor reflex

Crossed extensor reflex

Question 7

What is the flexor reflex?

Answer 7

Noxious stimulus causes the limb to flex by:
Contraction of flexor muscles via excitatory interneurons
Relaxation of extensor muscle via excitatory and inhibitor internueons

Question 8

What is the crossed extensor reflex?

Answer 8

Noxious stimulus causes the limb to extend via:
Contraction of extensor muscles via excitatory interneurons
Relaxation of flexor muscles via excitatory and inhibitory interneurons

Question 9

What does the crossed extensor reflex enhance?

Answer 9

Postural support during withdrawal of a foot from a painful stimulus

Question 10

What are the descending spinal tracts concerned with?

Answer 10

Control of movement 
Muscle tone
Spinal reflexes 
Spinal autonomic functions 
Modulation of sensory transmission

Question 11

Describe the lateral descending pathways

Answer 11

Under control from the cerebral cortex

Important for voluntary control of distal musculature

Question 12

Describe the ventromedial pathways

Answer 12

Under control from brain stem

Important for posture and locomotion

Question 13

Which pathways make up the lateral pathways?

Answer 13

Lateral corticospinal

Rubrospinal

Question 14

Which pathways makeup the ventromedial pathways?

Answer 14

Pontine reticulospinal 
Medullary reticulospinal 
Lateral vestibulospinal tract
Tectospinal tract
Ventral corticospinal tract

Question 15

Where do axons in the corticospinal tract decussate?

Answer 15

85% at medullary pyramids to form the lateral corticospinal tract
Remainder stay ipsilateral to form the ventral corticospinal tract to decussate more caudally

Question 16

Where will axons of the corticospinal tract terminate?

Answer 16

Dorsolateral region of ventral horn of grey matter

Location of LMNs and interneurons controlling distal muscle particular flexors

Question 17

Where are the cell bodies of the rubrospinal tract found?

Answer 17

Red nucleus - receives input from the motor cortex and cerebellum

Question 18

Where will axons of the rubrospinal tract decussate?

Answer 18

Ventral tegmental decussation and descend the spinal cord ventrolateral to the lateral corticospinal tract terminating at the ventral horn

Question 19

What is the function of the rubrospinal tract?

Answer 19

Exerts control over limb flexor muscles exciting LMNs of those muscles

Question 20

What are lesions of the lateral columns associated with?

Answer 20

Loss of fractionated movements
Slowing and impairment of accuracy of voluntary movements
Little effect on posture

Question 21

Where are cell bodies of the vestibulospinal tracts found?

Answer 21

Vestibular nuclei

Question 22

Where will the vestibular nuclei receive input?

Answer 22

CN 8
Vestibular labyrinths
Cerebellum

Question 23

Where will axons from the lateral vestibular nucleus descend?

Answer 23

Ipsilaterally as the lateral vestibulospinal tract as far as the lumbar spinal cord

Question 24

What is the function of the lateral vestibulospinal tract?

Answer 24

Upright position

Balanced posture by facilitating extensor MNs of antigravity muscles

Question 25

Where will axons from the medial vestibular nucleus descend?

Answer 25

Medial vestibulospinal tract as far as the cervical spinal cord

Question 26

What is the function of the medial vestibulospinal tract?

Answer 26

Activates cervical spinal circuits that control neck and back muscles guiding head movement

Question 27

Where do the cell bodies from the tectospinal tract reside?

Answer 27

Superior colliculus

Question 28

What input does the tectospinal tract receive?

Answer 28

Retina
Visual cortex
Afferents conveying somatosensory and auditory info

Question 29

Where will axons from the tectospinal tract run?

Answer 29

Decussate in dorsal tegmental decussation

Descend close to the midline to the cervical spinal cord

Question 30

What is the function of the tectospinal tract?

Answer 30

Influences muscles of neck, upper trunk and shoulders

Question 31

What is the function of the superior colliculus?

Answer 31

Map of the external world guiding the orientation of the head and eyes to visual stimulus

Question 32

Where do the pontine and medullary reticulospinal tracts arise from?

Answer 32

Reticular formation

Question 33

What is the course of the pontine reticulospinal tract?

Answer 33

Descends ipsilaterally

Question 34

What is the function of the pontine reticulospinal tract?

Answer 34

Enhances antigravity reflexes

Helps to maintain a standing posture by facilitating contraction of extensors of lower limbs

Question 35

What is the course of the medullary reticulospinal tract?

Answer 35

Descends bilaterally

Question 36

What is the function of the medullary reticulospinal tract?

Answer 36

Opposes the action of the pontine tract

Releases antigravity muscles from reflex control