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3rd Year - Neurology > Peter's Physiology 6 - Spinal nerves, upper motor neurones and control of movement > Flashcards

Peter's Physiology 6 - Spinal nerves, upper motor neurones and control of movement Flashcards

1
Q

Which type of neurones allow communication between sensory and motor neurones in the CNS?

A

Interneurones

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2
Q

What 4 sources do spinal interneurons receive input from

A

Primary sensory axons
Descending axons from the brain
Collaterals (branches) of LMNs
Other interneurones

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3
Q

What type of signal can inputs to spinal interneurones be?

A

Excitatory or inhibitory (interneurones integrate incoming information to generate an output)

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4
Q

What are the 2 types of spinal interneurones?

A

Excitatory

Inhibitory

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5
Q

What 2 responses do inhibitory interneurones mediate in order to provide co-cordinate control of flexors and extensors in limb movement?

A

Inverse myotatic response

Reciprocal inhibition between extensor and flexor muscles

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6
Q

What is the inverse myotatic response?

Other name

A

Glogli tendon reflex

Skeletal muscle contraction causes the antagonist muscle to simultaneously lengthen and relax

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7
Q

What is reciprocal inhibition between extensor and flexor muscles?

A

Muscles on one side of a muscle real to accommodate contraction on the other side of that joint

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8
Q

What is another name for the myotatic reflex?

A

Stretch reflex

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9
Q

At a joint, voluntary contraction of an extensor will stretch an antagonist flexor, initiating what?
How is unopposed extension therefore brought about?

A

The myotatic reflex

Descending pathways that activate the alpha-MN controlling the extensors muscles also, via inhibitory interneurons, inhibit the alpha-MNs supplying the antagonist muscles (reciprocal inhibition)

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10
Q

What tract do neurones from the motor cortex travel down in reciprocal inhibition?

A

Corticospinal tract

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11
Q

What pathways do excitatory interneurones mediate?

A

Flexor reflex

Crossed extensor reflex

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12
Q

How does a noxious stimulus cause a limb to flex?

What is this reflex called?

A

Contraction of flexor muscles via excitatory interneurones
Relaxation of extensor muscles via excitatory and inhibitory interneurones

Flexor reflex

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13
Q

How does a noxious stimulus cause a limb to extend?

What is this reflex called?

A

Contraction of extensor muscles via excitatory internueornes
Relaxation of flexor muscles via excitatory and inhibitory interneurones

Crossed extensor reflex

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14
Q

What is the purpose of the crossed extensor reflex?

A

To enhance postural support during withsrawal of a foot from a painful stimulus (don’t want to fall over)

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15
Q

What are central pattern generators?

A

biological neural networks that produce rhythmic patterned outputs without sensory feedback

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16
Q

What type of activity can a simple spinal central pattern generator command?

A

Rhythmic, alternating activity that moves a limb

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17
Q

To produce a simpel spinal central pattern generator that can command rhythmic alternating activity that moves a limb, what must the excitatory interneurone display in terms of activity?

A

Oscillatory, or pacemaker, activity

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18
Q

What type of motor function do high level structures control?
What 2 structures are classified as high level?

A

Strategy
Neocortical association areas
Basal ganglia

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19
Q

What type of motor function do middle level structures control?
What 2 structures are classified as middle level?

A

Tactics
Motor cortex
Cerebellum

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20
Q

What type of motor function do low level structures control?

What 2 structures are classified as low level?

A

Execution
Brain stem
Spinal cord

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21
Q

In terms of motor control hierarchy, what is strategy?

A

Aim of movement?

How can it best be achieved?

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22
Q

In terms of motor control hierarchy, what is tactics?

A

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

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23
Q

In terms of motor control hierarchy, what is execution?

A

Activation of motor pools and interneurone polls that command the desired movement and make essential postural adjustments

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24
Q

From which 2 areas do descending spinal tracts origiante from?

A

Cerebral cortex

Brain stem

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25
Q

What are the 2 important groups of descending spinal tracts?

A

Lateral pathways

Ventromedial pathways

26
Q

What 2 pathways make up the lateral descending pathways?

A

Lateral corticospinal tract

Rubrospinal tract

27
Q

What 4 important pathways make up the ventromedial descending pathways?

A

Pontine reticulospinal tract
Medullary reticulospianl trat
Lateral vestibulospinal tract
Tectospinal tract

28
Q

What structure control input to the lateral descending spinal tracts?

A

Cerebral cortex

29
Q

What actions are the lateral descending spinal tract pathways important for?

A

Voluntary control of distal musculature, particularly discrete, skilled movements e.g. hands and fingers in a “fractionated” manner

30
Q

What structure controls input to the ventromedial spinal tract pathways?

A

Brainstem

31
Q

What actions are the ventromedial pathways important for?

A

Control of posture and locomotion

32
Q

What is another name for the corticospinal tract?

A

Pyramdial tract

33
Q

Where are cell bodies of the corticospinal tract located?

A

About 2/3rds = motor cotetx

About 1/3rd = somatosensory areas of parietal cortex

34
Q

What does the axons of the corticospinal tract form at the medulla?

A

Medullary pyramid

35
Q

Where do most fibres in the corticospinal tract decussate?

A

At the pyramidal decussation (on medulla)

36
Q

What do the decussated fibres of the corticospinal tract form at the pyramidal decussation?
What are the remainder of fibres called?

A

Lateral corticospinal tract

Ventral corticospinal tract (decussate more caudally)

37
Q

Where do axons of the corticospinal tracts terminate?

A

In the dorsolateral region of the ventral horn and intermediate grey

38
Q

In terms of the corticospinal tract, what side of muscualture does the left hemisphere control?

A

Right musculature

39
Q

Where are the cell bodies of the rubrospinal tract located?

What does this receive input from?

A 
Red nucleus (midbrain)
Motor cortex and cerebellum
40
Q

Where do axons of the rubrospinal tract decussate?

A

At the ventral segmental decussation in the midbrain

41
Q

Where do axons of the rubrospinal tracts terminate?

A

Ventral horn

42
Q

What do axons of the rubrospinal tract control?

A

Limb flexor muscles

43
Q

What 2 problems can lesions of the lateral descending pathways cause?

A

Loss of “fractionated” movements i.e. shoulders elbow, wrist and fingers cannot be moved independently
Slowing and imapirment of accuracy of voluntary movements

44
Q

What difference to the problems caused by a lesion to the lateral descending pathways can occur if the rubospinal tract is spared?

A

Initially causes same deficits as pronoun lesions although major recovery can occur (due to rubrospinal tracts taking over)

45
Q

Where do the cell bodies of the vestibulospinal tracts reside?

A

Vestibular nuclei (lateral and medial) in the pons

46
Q

What do the vestibulospinal tracts receive input from?

A 
Vestibular larbyrinthys (via CN VIII)
Cerebellar input also important
47
Q

Where do axons from the lateral vestibular nucleus descend to?
How do they do this?

A

Lumbar spinal cord

Via the lateral vestibulospinal tract

48
Q

Do inputs to the vestibulospinal tracts control the ipsilateral or contralateral sides of the body?

A

Ipsilateral

49
Q

What do outputs from the lateral vestibulospinal tract do?

A

Helps to hold us upright and balance upright by facilitating extensor MNs of antigravity muscles e.g. of the leg

50
Q

Where do axons from the medial vestibular nucleus descend to?
How do they do this?

A

Cervical spinal cord

Via the medial vestibulospinal tract

51
Q

What do outputs from the medial vestibulospinal tract do?

A

Activate cervical spinal circuits that control neck and back muscles guiding head movements

52
Q

Where do the cell bodies of the tectospinal tract reside?

A

In the superior colliculus of the midbrain

53
Q

What does the tectospinal tract receive input from?

A

Retina
Visual cortex
Afferents conveying somatosensory and auditory information

54
Q

Where do axons of the tectospinal tract decussate?

A

In the dorsal tegmental decussation of the midbrain

55
Q

Give an example of an action the tectospinal tract controls?

A

Orientation of the head and eyes to an important, new, visual stimulus

56
Q

Which is the medial and which is the lateral reticulospinal tracts?

A 
Medial = pontine
Lateral = medullarly
57
Q

Where do both reticulospinal tracts arise?

A

Reticular formation

58
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

59
Q

Does the pontine reticulospinal tract descend ispilaterally, contralaterally or bilaterally?

A

Ipsilaterally

60
Q

What 2 functions does the pontine reticulospinal tract mediate?

A

Enhances antigravity reflexes of the spinal cord

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

61
Q

Does the medullary reticulospinal tract descend ispilaterally, contralaterally or bilaterally?

A

Bilaterally

62
Q

What 2 functions does the medullary reticulospinal tract mediate?

A

Opposes the action of the medial tract

Releases antibgravity muscles from reflex control

3rd Year - Neurology (17 decks)

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