UMNs and Control of Movement

Question 1

What is the function of a simple spinal central pattern generator?

Answer 1

Can command rhythmic, alternating activity that moves a limb

Question 2

What is the essential features of a simple spinal central pattern generator?

Answer 2

Excitatory interneuron displays oscillatory (pacemaker) activity

Question 3

How many levels are involved in the motor control hierarchy?

Answer 3

At least three levels

Question 4

How are controlled movements initiated and influenced?

Answer 4

By multiple sensory inputs and a need to move using internal mechanisms

Question 5

What is the motor control hierarchy at its simplest?

Answer 5

High = neocortical association areas and basal ganglia
Middle = motor cortex and cerebellum
Low = brainstem and spinal cord

Question 6

Where do the descending spinal tracts arise from?

Answer 6

Cerebral cortex and brainstem

Question 7

What are the descending spinal tracts involved in?

Answer 7

Control of movement, muscle tone, spinal reflexes, spinal autonomic functions and modulation of sensory transmission to higher centres

Question 8

What are the two important divisions of the descending spinal tract?

Answer 8

Lateral and ventromedial

Question 9

What is the lateral pathway of the descending spinal tract involved in?

Answer 9

Voluntary control of distal musculature = under control from cerebral cortex

Question 10

What is the ventromedial pathway of the descending spinal tract involved in?

Answer 10

Control of posture and locomotion = under control of brainstem

Question 11

What is the major lateral pathway of the descending spinal tract?

Answer 11

Corticospinal tract = longest and one of largest CNS tract

Question 12

Where are the cell bodies of the corticospinal tract located?

Answer 12

Motor cortex (BA4 and BA6) and somatosensory areas of the parietal cortex

Question 13

Where do the axons of the corticospinal tract flow?

Answer 13

To the base of the medulla forming a tract (the medullary pyramid)

Question 14

Where do most fibres of the corticospinal tract cross?

Answer 14

At the pyramidal decussation = forms the lateral corticospinal tract

Question 15

What happens to fibres of the corticospinal tract that don’t cross at the pyramidal decussation?

Answer 15

Stay ipsilateral to form the ventral corticospinal tract and decussate more caudally

Question 16

Where do axons of the corticospinal tract terminate?

Answer 16

In the dorsolateral region of the ventral horn and intermediate grey (location of LMNs and interneurons controlling distal muscles)

Question 17

What side of the body do the motor centres of the left hemisphere control?

Answer 17

The right side of the body

Question 18

What is a minor lateral pathway of the descending spinal tract?

Answer 18

The rubrospinal tract = exerts control over limb flexor muscle by exciting LMNs

Question 19

Where are the cell bodies of the rubrospinal tract located?

Answer 19

In the red nucleus = receives input from the motor cortex and cerebellum

Question 20

Where do the axons of the rubrospinal tract cross over?

Answer 20

Decussate at ventral tegmental decussation = descend spinal cord ventrolateral to the lateral corticospinal tract

Question 21

Where do axons of the rubrospinal cord terminate?

Answer 21

In the ventral horn

Question 22

What are lesions of the lateral column associated with?

Answer 22

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

Question 23

What are some features of lesions to the corticospinal tract alone?

Answer 23

Deficits are as profound as those of lateral column but major recovery can occur
Weakness of distal flexors and inability to move fingers independently persists

Question 24

What are the ventromedial pathways?

Answer 24

Vestibulospinal tract, tectospinal tract, pontine reticulospinal tract, medullary reticulospinal tract

Question 25

Where are the cell bodies of the vestibulospinal tract located?

Answer 25

Reside in vestibular nuclei = receive input via CN VIII from the vestibular labyrinths

Question 26

Where do the axons from the lateral vestibular nucleus descend?

Answer 26

Descend from Deiter's nucleus ipsilaterally as the lateral vestibulospinal tract as far as the lumbar spinal cord = balanced posture

Question 27

Where do the axons from the medial vestibular nucleus descend?

Answer 27

Descend as far as the medial vestibulospinal tract as far as the cervical spinal cord = activate cervical spinal circuits that control neck and back muscles

Question 28

Where are the cell bodies of the tectospinal tract located?

Answer 28

Reside in superior colliculus = receives input directly from the retina and also from the visual cortex and afferents conveying somatosensory/auditory info

Question 29

Where do the axons of the tectospinal tract cross over?

Answer 29

Decussate in the dorsal tegmental decussation = descend close to midbrain as the tectospinal tract to the cervical spinal cord

Question 30

What does the superior colliculus act as in the tectospinal tract?

Answer 30

A map of the external world

Question 31

Where does the pontine (medial) reticulospinal tract arise?

Answer 31

From the reticular formation = controlled by descending signals from the cortex and descends ipsilaterally

Question 32

What does the pontine reticulospinal tract control?

Answer 32

Enhances antigravity reflexes of the spinal cord | Helps to maintain a standing posture by facilitating contraction of the extensors of lower limbs

Question 33

Where does the medullary (lateral) reticulospinal tract arise?

Answer 33

From the reticular formation = controlled by descending signals from the cortex and descends bilaterally

Question 34

What is the function of the medullary reticulospinal tract?

Answer 34

Opposes the action of the medial tract | Releases antigravity muscles from reflex control