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Neurology > Spinal Reflexes, Upper Motor Neurones and Control of Movement > Flashcards

Spinal Reflexes, Upper Motor Neurones and Control of Movement Flashcards

1
Q

What do spinal interneurones receive input from?

A
  • Primary sensory axons.
  • Descending axons from the brain.
  • Collaterals (branches) of LMN’s.
  • Other interneurons.
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2
Q

What can input to spinal neurones be either?

A

Excitatory
OR
Inhibitory

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3
Q

What generate incoming info to generate an output?

A

Interneurones

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4
Q

Interneurones are either excitatory or inhibitory

A

TRUE

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5
Q

What do inhibitory interneurones mediate?

A
  • The inverse myotatic response.

* RECIPROCAL INHIBITION between extensor and flexor muscles

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6
Q

What is reciprocal inhibition important in the initiation of?

A

Movement by the motor cortex

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7
Q

At a joint, what will the voluntary contraction of an extensor stretch?

A

An antagonistic flexor

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8
Q

What does stretching of an antagonistic flexor do?

A

Initiates the myotatic reflex

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9
Q

Once this myotatic reflex is initiated, however, what happens to allow unopposed extension to still occur?

A

The descending pathways that activate the α-MN controlling the extensor muscles also, via inhibitory interneurons, inhibit the α-MNs supplying the antagonist muscles

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10
Q

What do excitatory interneurones mediate?

A
  • The flexor reflex.

* The crossed extensor reflex

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11
Q

Describe the flexor reflex.

A

A noxious stimulus causes limb to flex by:

  • contraction of flexor muscles by EXCITATORY INTERNEURONES.
  • relaxation of extensor muscles via EXCITATORY + INHIBITORY INTERNEURONES.
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12
Q

Describe the crossed extensor reflex.

A

A noxious stimulus causes limb to extend by:

  • contraction of extensor muscles via EXCITATORY interneurons.
  • relaxation of flexor muscles via EXCITATORY + INHIBITORY interneurons
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13
Q

Why is the crossed extensor reflex important?

A

It enhances postural support during withdrawal of a foot from a painful stimulus so you don’t fall over

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14
Q

What are the controlled movements of the body influenced by?

A
  • Multiple sensory inputs.

* A need to move using internal mechanisms

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15
Q

What is found high in the brain? What is its function?

A

Strategy area
Neocortical areas
Basal ganglia

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16
Q

What is found in the middle of the brain? What is its function?

A

Tactics area
Motor cortex
Cerebellum

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17
Q

What is found low in the brain? What is its function?

A

Execution
Brain stem
Spinal cord

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18
Q

Where do the descending spinal tracts originate from?

A

The cerebral cortex and brain stem

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19
Q

What functions are the descending spinal cord tracts concerned with?

A 
1 – Control of movement. 
2 – Muscle tone. 
3 – Spinal reflexes. 
4 – Spinal autonomic functions. 
5 – Modulation of sensory transmission to higher centres
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20
Q

Name 2 important descending spinal tracts.

A

Lateral + Ventromedial

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21
Q

What are lateral pathways under the control of?

A

Cerebral cortex

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22
Q

What are lateral pathways important for?

A

Voluntary control of distal musculature, particularly discrete, skilled, movements (ie. hands and fingers in a ‘fractionated’ manner)

23
Q

What are ventromedial pathways under the control of?

A

Brain stem

24
Q

What are ventromedial pathways important for?

A

Posture and locomotion

25
Q

Name a minor lateral pathway.

A

The rubrospinal tract

26
Q

Where are the cell bodies of the rubrospinal tract located?

A

In the red nucleus, which receives input from the motor cortex and cerebellum

27
Q

Where do axons of the rubospinal tract decussate?

A

At the ventral tegmental decussation

28
Q

Once axons of the rubospinal tract have decussated, what do they do?

A

Descend the spinal cord ventrolateral to the lateral corticospinal tract

29
Q

Where do axons of the rubospinal tract terminate?

A

Ventral horn

30
Q

What are the effects of lesions of the lateral collumns?

A
  • Loss of ‘fractionated’ movements ie. shoulders, elbow, wrist and fingers can’t be moved independently.
  • Slowing and impairment of accuracy of voluntary movements.
  • Little effect on normal posture (ie. standing and sitting).
31
Q

Describe the deficits caused by lesions of the corticospinal tract alone.

A

Deficits are as profound as those caused by a lesion of the lateral columns, but over time, major recovery can occur

32
Q

Although recovery can occur from deficits caused by lesions of the cortiospinal tract, what can occur?

A

Weakness of the distal flexors, and an inability to move fingers independently

33
Q

When does recovery of lesions of the corticospinal tract not occur?

A

If the rubospinal tract is also lesioned

34
Q

Where are the cell bodies of the vestibulospinal tract located?

A

In the vestibular nuclei (lateral and medial).

35
Q

Where do vestibular nuclei receive input from? What is this via?

A

From the vestibular labyrinths – via CN VIII.

Cerebellar input is also important

36
Q

Describe how axons from the lateral vestibular nucleus (Deiter’s nucleus) descend.

A

Descend ipsilaterally as the lateral vestibulospinal tract as far as the lumbar spinal cord

37
Q

What do Deiter’s nucleus help to do?

A

Hold upright and balanced posture by facilitating extensor MNs of antigravity muscles (ie. of the leg).

38
Q

What do the axons of the medial vestibular nucleus descend as? Where to?

A

Descend as the medial vestibulospinal tract, as far as the cervical spinal cord

39
Q

What do medial vestibular nucleus axons activate?

A

Cervical spinal circuits that control neck and back muscles, guiding head movements

40
Q

Where are the cell bodies of the tectospinal tract located?

A

In the superior colliculus (aka optic tectum)

41
Q

Where does the superior colliculus receive input from?

A
  • Direct input – from the retina.
  • From visual cortex.
  • Afferents conveying somatosensory and auditory information.
42
Q

Where do axons of the tectospinal tract decussate?

A

In the dorsal tegmental decussation

43
Q

After decussation, describe how axons of the tectospinal tract descend?

A

Descend close to the midline as the tectospinal tract to the cervical spinal cord, influencing the muscles of the neck, upper trunk and shoulders

44
Q

What does the superior colliculus act as?

A

A map of the external world, guiding orientation of the head and eyes to an important, new, visual stimulus

45
Q

Where do Pontine (medial) + Medullary (lateral) Reticulospinal Tracts arise from?

A

Reticular formation

46
Q

What is the reticular formation?

A

A diffuse mesh of neurones that are located along the length, and at the core of the brainstem

47
Q

How does the pontine tract descend in the spinal cord?

A

IPSILATERALLY

48
Q

Where does the pontine tract enhance?

A

Anti-gravity reflexes of the spinal cord

49
Q

What is the function of the pontine tract?

A

A standing posture.

By facilitating contraction of the extensors of the lower limbs

50
Q

How does the medullary tract descend?

A

BILATERALLY

51
Q

What does the medullary tract oppose?

A

The action of the medial tract

52
Q

What does the medullary tract do to anti-gravity muscles?

A

Releases them from reflex control

53
Q

What is activity in both the pontine and medullary reticulospinal tracts controlled by?

A

Descending signals from the cortex

Neurology (42 decks)

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