UMNs and Control of Movement Flashcards

1
Q

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

A

Can command rhythmic, alternating activity that moves a limb

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2
Q

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

A

Excitatory interneuron displays oscillatory (pacemaker) activity

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3
Q

How many levels are involved in the motor control hierarchy?

A

At least three levels

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4
Q

How are controlled movements initiated and influenced?

A

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

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5
Q

What is the motor control hierarchy at its simplest?

A
High = neocortical association areas and basal ganglia
Middle = motor cortex and cerebellum
Low = brainstem and spinal cord
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6
Q

Where do the descending spinal tracts arise from?

A

Cerebral cortex and brainstem

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7
Q

What are the descending spinal tracts involved in?

A

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

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8
Q

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

A

Lateral and ventromedial

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9
Q

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

A

Voluntary control of distal musculature = under control from cerebral cortex

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10
Q

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

A

Control of posture and locomotion = under control of brainstem

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11
Q

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

A

Corticospinal tract = longest and one of largest CNS tract

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12
Q

Where are the cell bodies of the corticospinal tract located?

A

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

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13
Q

Where do the axons of the corticospinal tract flow?

A

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

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14
Q

Where do most fibres of the corticospinal tract cross?

A

At the pyramidal decussation = forms the lateral corticospinal tract

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15
Q

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

A

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

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16
Q

Where do axons of the corticospinal tract terminate?

A

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

17
Q

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

A

The right side of the body

18
Q

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

A

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

19
Q

Where are the cell bodies of the rubrospinal tract located?

A

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

20
Q

Where do the axons of the rubrospinal tract cross over?

A

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

21
Q

Where do axons of the rubrospinal cord terminate?

A

In the ventral horn

22
Q

What are lesions of the lateral column associated with?

A

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

23
Q

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

A

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

24
Q

What are the ventromedial pathways?

A

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

25
Q

Where are the cell bodies of the vestibulospinal tract located?

A

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

26
Q

Where do the axons from the lateral vestibular nucleus descend?

A

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

27
Q

Where do the axons from the medial vestibular nucleus descend?

A

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

28
Q

Where are the cell bodies of the tectospinal tract located?

A

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

29
Q

Where do the axons of the tectospinal tract cross over?

A

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

30
Q

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

A

A map of the external world

31
Q

Where does the pontine (medial) reticulospinal tract arise?

A

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

32
Q

What does the pontine reticulospinal tract control?

A

Enhances antigravity reflexes of the spinal cord

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

33
Q

Where does the medullary (lateral) reticulospinal tract arise?

A

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

34
Q

What is the function of the medullary reticulospinal tract?

A

Opposes the action of the medial tract

Releases antigravity muscles from reflex control