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CNS CLERKSHIP > Spinal Reflexes, UMN and Control of Movement > Flashcards

Spinal Reflexes, UMN and Control of Movement Flashcards

1
Q

Spinal interneurons receive input from?

A
  • Primary sensory axons (Ia and Ib fibres).
  • Descending axons from the brain.
  • Collaterals (branches) of LMNs.
  • Other interneurons.
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2
Q

Input to spinal interneurons may be either?

A

Excitatory or inhibitory.

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3
Q

Interneurons integrate incoming information to generate what?

A

An output.

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4
Q

Inhibitory interneurons mediate?

A
  • Inverse myotatic response.

- Reciprocal inhibition between extensor and flexor muscles.

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5
Q

Describe the myotatic reflex.

A

Causes the homonymous extensor muscle (quadriceps) to contract - but for the leg to extend, the antagonist flexor muscle (hamstring) must simultaneously relax.

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6
Q

With regards to myotatic reflex:

Describe the connection between the Ia afferent from the muscle spindle extensor and the homonymous muscle.

A

Ia afferent from muscle spindle extensor makes excitatory monosynaptic contact with the a-MN innervating the homonymous muscle.

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7
Q

With regards to myotatic reflex:

Which pathway involves an inhibitory interneurone?

A

A polysynaptic pathway.

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8
Q

With regards to myotatic reflex:

The Ia fibre inhibits what?

A

The a-MN supplying the flexor muscle.

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9
Q

Reciprocal inhibition is important in the initiation of movement by which cortex?

A

Motor cortex.

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10
Q

At a joint, voluntary contraction of an extensor will stretch an antagonist flexor, initiating what?

A

The myotatic reflex.

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11
Q

Descending pathways activating the a-MN controlling extensor muscles also inhibit a-MNs supplying antagonist muscles via what?

A

Inhibitory neurons.

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12
Q

Descending pathways activating the a-MN controlling extensor muscles also inhibit a-MNs supplying antagonist muscles to allow what?

A

Unopposed extension.

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13
Q

Excitatory interneurons mediate?

A
  • Flexor reflex.

- Crossed extensor reflex.

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14
Q

With regards to the flexor reflex, noxious stimulus causes a limb to flex by?

A
  • Contraction of flexor muscles via excitatory interneurones.
  • Relaxation of extensor muscles via excitatory and inhibitory interneurones.
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15
Q

With regards to the crossed extensor reflex, noxious stimulus causes a limb to extend by?

A
  • Contraction of extensor muscles via excitatory interneurons.
  • Relaxation of flexor muscles via excitatory and inhibitory interneurons.
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16
Q

What reflex enhances postural support during withdrawal of a foot from a painful stimulus?

A

Crossed extensor reflex.

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17
Q

A simple spinal central pattern generator (CPG) can command what limb activity?

A
  • Rhythmic, alternating activity that moves a limb.
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18
Q

What is the essential feature for an excitatory interneurone to display?

A

Oscillatory or pacemaker activity.

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19
Q

Controlled movements of the body (motor control) are initiated/influenced by?

A
  • Multiple sensory inputs.

- A need to move using internal mechanisms.

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20
Q

What is the function of high level brain structures e.g. neocortical association areas and basal ganglia, in motor control?

A
  • Strategy.
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21
Q

What is the function of middle level brain structures e.g. motor cortex and cerebellum, in motor control?

A
  • Tactics.
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22
Q

What is the function of low level structures e.g. brain stem and spinal cord, in motor control?

A
  • Execution.
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23
Q

Describe “strategy” in terms of motor control.

A
  • What is the aim of the movement?

- How is the movement best achieved?

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24
Q

Describe “tactics” in terms of motor control.

A
  • What sequence of muscle contractions and relaxations in time and space will fulfil the strategic aim?
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25
Q

Describe “execution” in terms of motor control.

A
  • Activation of motor pools and interneuron pools that command desired movements and make essential postural adjustments.
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26
Q

Descending spinal tracts originate where?

A
  • Cerebral cortex.

- Brain stem.

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27
Q

Descending spinal tracts are involved in what?

A
  • Control of movement.
  • Muscle tone.
  • Spinal reflexes.
  • Spinal autonomic functions.
  • Modulation of sensory transmission to higher centres.
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28
Q

Lateral descending pathways are under control from what?

A
  • Cerebral cortex.
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29
Q

Lateral descending pathways are important for voluntary control of what?

A
  • Distal musculature, particularly in discrete, skilled movements.
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30
Q

Ventromedial descending pathways are under control from what?

A

The brainstem.

31
Q

Ventromedial descending pathways are important for control of what?

A

Posture and locomotion.

32
Q

The major lateral descending pathway is what?

A

Corticospinal (pyramidal) tract.

33
Q

Where are the cell bodies of the corticospinal tract?

A
  • Motor cortex (about 2/3).

- Somatosensory areas of parietal cortex (1/3).

34
Q

Axons of the corticospinal tract course to the base of the medulla to form a tract known as?

A

The medullary pyramid.

35
Q

Most fibres of the corticospinal tract decussate where?

A

Pyramidal decussation to form lateral corticospinal tract (75-90%).

36
Q

The majority of corticospinal fibres decussate at the pyramidal decussation, what happens to the rest?

A

Remainder stay ipsilateral to form the ventral corticospinal tract and decussate more caudally.

37
Q

Where do axons of the corticospinal tract terminate?

A

In the dorsolateral region of the ventral horn and intermediate grey.

38
Q

The termination of axons of the corticospinal tract is the location of what?

A

LMNs and interneurons controlling distal muscles - particularly flexors.

39
Q

Irrespective of the level of decussation, the left hemisphere of the brain controls which musculature?

A

Right musculature.

40
Q

Name a minor lateral descending pathway that is phylogenetically older than the corticospinal tract.

A

Rubrospinal tract.

41
Q

Where are the cell bodies of the rubrospinal tract located?

A

Red nucleus.

42
Q

The cell bodies of the rubrospinal tract are located in the red nucleus, which receives input from what?

A
  • Motor cortex and the cerebellum.
43
Q

Where do axons of the rubrospinal tract decussate?

A

Ventral tegmental decussation.

44
Q

Where do axons of the rubrospinal tract descend after decussating?

A

The spinal cord ventrolateral to the lateral corticospinal tract.

45
Q

Where do axons of the rubrospinal tract terminate?

A

Ventral horn.

46
Q

The rubrospinal tract exerts control over what?

A

Limb flexor muscles by exciting LMNs of those muscles.

47
Q

Lesions of the lateral columns are associated with?

A
  • Loss of fractionated movements.
  • Slowing and impaired accuracy of voluntary movements.
  • Little effect on normal posture.
48
Q 
A person with:
- Loss of fractionated movements.
- Slow and impaired accuracy of voluntary movements.
- Little effect on normal posture.
Most likely has a lesion where?
A

Lateral columns.

49
Q

A lesion of the corticospinal tract alone initially causes what?

A

Deficits as profound as a lesion of the lateral column, but may recover over time.

  • But weakness of distal flexors and inability to move fingers independently persist.
50
Q

A lesion of the corticospinal tract will recover with time, but this recovery is reversed if there is also a lesion where?

A

The rubrospinal tract.

51
Q

Where do cell bodies of the vestibulospinal tracts reside?

A

In the vestibular nuclei (lateral and medial).

52
Q

Cell bodies of vestibulospinal tract reside in the lateral and medial vestibular nuclei that receive input via which CN?

A

CN VIII - vestibular nerve.

53
Q

Cell bodies of vestibulospinal tract reside in the lateral and medial vestibular nuclei that receive input via CN VIII from where?

A

Vestibular labyrinths + cerebellum.

54
Q

Axons of the vestibulospinal tracts from the lateral vestibular nucleus (Deiter’s nucleus) descend ipsilaterally as what?

A

Lateral vestibulospinal tract.

55
Q

Axons of the vestibulospinal tracts from the lateral vestibular nucleus (Deiter’s nucleus) descend ipsilaterally as the lateral vestibulospinal tract as far as where?

A

The lumbar spinal cord.

56
Q

The lateral vestibulospinal tract aids in what?

A

Holding body upright and balancing posture by facilitating extensor MNs of anti-gravity muscles.

57
Q

Axons of the vestibulospinal tracts from the medial vestibular nucleus descend as what?

A

The medial vestibulospinal tract.

58
Q

Axons of the vestibulospinal tracts from the medial vestibular nucleus descend until where?

A

The cervical spinal cord.

59
Q

Axons of the vestibulospinal tracts from the medial vestibular nucleus activate what?

A

Cervical spinal circuits controlling the neck and back muscles that guide head movements.

60
Q

Where do cell bodies of the tectospinal tract reside?

A

Superior colliculus/optic tectum.

61
Q

The superior colliculus/optic tectum receives direct input from where?

A

The retina, visual cortex and afferents conveying somatosensory and auditory information.

62
Q

Axons of the tectospinal tract decussate where?

A

Dorsal tegmental decussation.

63
Q

Axons of the tectospinal tract decussate at the dorsal tegmental decussation and then descend where?

A

Close to midline as the tectospinal tract.

64
Q

The tectospinal tract influences what?

A

Movement of the muscles of the neck, upper trunk and shoulders in reflex to visual stimuli.

65
Q

The superior colliculus may guide the orientation of the head and eyes to what?

A

Important, new visual stimuli.

66
Q

The pontine and medullary reticulospinal tracts arise from what?

A

The reticular formation.

67
Q

What is the reticular formation?

A

Diffuse mesh of neurons located along the length and at the core of the brainstem.

68
Q

The pontine (medial) reticulospinal tract descends?

A

Ipsilaterally.

69
Q

What is the function of the pontine (medial) reticulospinal tract?

A
  • To enhance antigravity reflexes of the spinal cord.

- Aids maintenance of standing posture by facilitating contraction of extensors of lower limbs.

70
Q

The medullary (lateral) reticulospinal tract descends?

A

Bilaterally.

71
Q

Function of the medullary (lateral) reticulospinal tract?

A
  • Oppose action of the medial tract.

- Release antigravity muscles from reflex control.

72
Q

Pontine and medullary reticulospinal tracts are what type of pathways?

A

Ventromedial.

73
Q

Activity in both the pontine and medullary reticulospinal tracts is controlled by what?

A

Descending signals from the cortex.

CNS CLERKSHIP (43 decks)

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