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Second Year - Biomedical Sciences BS22001 > Lecture 11 - Neuromuscular Reflexes > Flashcards

Lecture 11 - Neuromuscular Reflexes Flashcards

1
Q

What are reflexes

A

Rapid, automatic responses generated by the circuitry of the spinal cord

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2
Q

What do reflexes coordinate

A

The action of muscle groups at the spinal level

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3
Q

When skeletal muscle is pulled, it pulls back and this is known as

A

The myotatic reflex

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4
Q

What is change in length/rate of muscle registered by

A

A sensory organ known as the muscle spindle

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5
Q

What type of arc is the myotatic reflex

A

A monosynaptic reflex arc

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6
Q

The stretch of a muscle spindle causes the activation of

A

Ia afferents

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7
Q

When the Ia afferents are stimulated this causes

A

The excitatory synaptic transmission in the spinal cord which activates the alpha motor neurone

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8
Q

When alpha motor neurones are stimulated they cause

A

The contraction of the homonymous muscle

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9
Q

What does the muscle spindle consist of

A

A fibrous capsule, intrafusal fibres, sensory afferents that innervate intrafusal fibres, and gamma motor neurone efferents that innervate the intrafusal fibres

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10
Q

What do intrafusal fibres consist of

A

A non-elastic equatorial region and contractile polar ends

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11
Q

What is the non-contractile equatorial region of the intrafusal fibre innervated by

A

Ia sensory neurones

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12
Q

What type of input does the contractile polar ends receive

A

Efferent input from gamma motor neurones

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13
Q

Where are the cell bodies from gamma motor neurones found

A

In the ventral horn of the spinal cord

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14
Q

What does stimulation of gamma motor neurones cause

A

The contraction of the muscle spindle

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15
Q

During voluntary movements, what alpha and gamma motor neurones are active

A

Both alpha and gamma motor neurones are co-activated

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16
Q

Why are alpha and gamma motor neurones both activated

A

So that the intrafusal fibres contract in parallel with the extrafusal fibres

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17
Q

What maintains the sensitivity of the muscle spindle

A

Alpha and gamma motor neurones being co-activated and the intrafusal and extrafusal fibres contracting in parallel

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18
Q

What are the two groups of intrafusal fibres

A

Nuclear bag fibres and chain fibres

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19
Q

Two types of nuclear bag fibres

A

Bag 1/dynamic and bag 2/static

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20
Q

Characteristics of bag 1 fibres

A

Very sensitive to the rate of change of muscle length and are innervated by dynamic gamma motor neurones

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21
Q

Characteristics of bag 2

A

Sensitive to the absolute length of the muscle and are innervated by static gamma motor neurones

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22
Q

Characteristics of chain fibres

A

Sensitive to the absolute length of the muscle and are innervated by static gamma motor neurones

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23
Q

What are the two types of afferent fibres that innervate intrafusal fibres

A

Ia afferents and II fibres

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24
Q

What do Ia afferents form

A

A primary annulospial nerve ending

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25
Q

What do II fibres form

A

A flowerspray ending on all intrafusal fibres except the bag 1 dynamic type

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26
Q

What do both types of afferent fibres respond to

A

Stretch

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27
Q

What are Ia fibres more sensitive to

A

The rate of change of the intrafusal fibre

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28
Q

What are II fibres more sensitive to

A

The absolute length of the intrafusal fibres

29
Q

Stimulation of the static gamma fibres causes

A

The static response to increase

30
Q

Which motor neurones are active in activities in which muscle length changes slowly and predictably

A

Only static gamma motor neurones

31
Q

Which motor neurones are active when muscle length changes rapidly and unpredictably

A

Dynamic gamma motor neurones

32
Q

Where are the Golgi tendon organs located

A

The junction of the muscle and tendon

33
Q

What do the Golgi tendon organs monitor

A

The changes in muscle tension

34
Q

What are Golgi tendon organs in series with

A

Extrafusal fibres

35
Q

What innervates the Golgi tendon organs

A

Ib sensory afferents

36
Q

Characteristics of Ib afferents

A

Myelinated and slightly slower conducting than Iafibres

37
Q

Where do group Ib afferents synapse

A

Upon inhibitory interneurones

38
Q

What do the inhibitory interneurones synapse upon

A

The alpha motor neurones

39
Q

What forms the basis of the inverse myotatic reflex

A

Ib afferents entering the spinal cord and synapse upon inhibitory interneurones, which in turn synapse upon the alpha motor neurones of the homonymous muscle

40
Q

What is the polysnaptic pathway

A

The way in which an inhibitory interneurone is interposed between the Ib afferents and alpha motor neurones

41
Q

What does the inverse myotatic reflex protect

A

The muscle from overloading

42
Q

As muscle tension increases, what occurs

A

Inhibition of alpha motor neurones slows its contraction

43
Q

When muscle tension falls, what occurs

A

The inhibition of the alpha motor neurone is reduced and muscle contraction increases

44
Q

Where are proprioceptive axons present

A

In connective tissue of joints

45
Q

What do proprioceptive axons respond to

A

Changes in angle, direction and velocity of movement of a joint

46
Q

What do the proprioceptive axons prevent

A

Excessive flexion and extension

47
Q

What are proprioceptive axons made up of

A

A mixture of rapidly adapting (RA) and slow adapting (SA) units that either have a high threshold (HT) or low threshold (LT) for activation

48
Q

Where are free nerve endings found

A

In the capsule and connective tissue

49
Q

What type of proprioceptive axons are found within free nerve endings

A

High threshold and slow adapting receptors

50
Q

What is the role of receptors in free nerve endings

A

They have a protective role

51
Q

Paciniform endings are found where

A

In the periosteum

52
Q

What type of proprioceptive axons are found within the paciniform endings

A

Low threshold and slow adapting receptors

53
Q

What are the proprioceptive axon receptors in the paciniform

A

The are accelerated detectors

54
Q

Where are ruffini endings found

A

Mainly in joint capsules

55
Q

What type of proprioceptor axons are found in the ruffini endings

A

Low threshold and slow adapting

56
Q

What do the proprioceptor axons within the ruffini endings do

A

They monitor the static position and speed of movements

57
Q

Where do spinal interneurones receive input from

A

Primary sensory organs (Ia and Ib fibres), descending axons from the brain, collaterals of the lower motor neurones and other interneurones

58
Q

What are the two types of interneurone input

A

Excitatory or inhibitory

59
Q

What do the inhibitory interneurones mediate

A

The inverse myotatic reflex and reciprocal inhibition between extensor and flexor muscles

60
Q

What do the interneurones integrate

A

Incoming information to generate an output

61
Q

What are the two types of interneurones

A

Excitatory and inhibitory

62
Q

What does the myotatic reflex cause

A

The homonymous extensor muscle to contract but the antagonist flexor muscle must simultaneously relax

63
Q

What is reciprocal inhibition important in

A

The inhibition of movement by the motor cortex

64
Q

What initiates the myotatic reflex

A

Voluntary contraction of an extensor muscle will stretch an antagonist flexor

65
Q

What do the excitatory interneurones mediate

A

The flexor reflex and crossed extensor reflex

66
Q

What happens in the flexor reflex

A

A noxious stimulus causes the limbs to flex by contraction of flexor muscles via excitatory interneurones and the relaxation of extensor muscles via excitatory and inhibitory interneurones

67
Q

What happens in the crossed extensor reflex

A

A noxious stimulus causes the limb to extend by contraction of the extensor muscles via excitatory interneurones and relaxation of the flexor muscle via excitatory and inhibitory interneurones

68
Q

What does the crossed extensor reflex enhance

A

Postural support during withdrawal of the foot from a painful stimulus

Second Year - Biomedical Sciences BS22001 (28 decks)

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