Lecture 11 - Neuromuscular Reflexes

Question 1

What are reflexes

Answer 1

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

Question 2

What do reflexes coordinate

Answer 2

The action of muscle groups at the spinal level

Question 3

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

Answer 3

The myotatic reflex

Question 4

What is change in length/rate of muscle registered by

Answer 4

A sensory organ known as the muscle spindle

Question 5

What type of arc is the myotatic reflex

Answer 5

A monosynaptic reflex arc

Question 6

The stretch of a muscle spindle causes the activation of

Answer 6

Ia afferents

Question 7

When the Ia afferents are stimulated this causes

Answer 7

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

Question 8

When alpha motor neurones are stimulated they cause

Answer 8

The contraction of the homonymous muscle

Question 9

What does the muscle spindle consist of

Answer 9

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

Question 10

What do intrafusal fibres consist of

Answer 10

A non-elastic equatorial region and contractile polar ends

Question 11

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

Answer 11

Ia sensory neurones

Question 12

What type of input does the contractile polar ends receive

Answer 12

Efferent input from gamma motor neurones

Question 13

Where are the cell bodies from gamma motor neurones found

Answer 13

In the ventral horn of the spinal cord

Question 14

What does stimulation of gamma motor neurones cause

Answer 14

The contraction of the muscle spindle

Question 15

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

Answer 15

Both alpha and gamma motor neurones are co-activated

Question 16

Why are alpha and gamma motor neurones both activated

Answer 16

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

Question 17

What maintains the sensitivity of the muscle spindle

Answer 17

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

Question 18

What are the two groups of intrafusal fibres

Answer 18

Nuclear bag fibres and chain fibres

Question 19

Two types of nuclear bag fibres

Answer 19

Bag 1/dynamic and bag 2/static

Question 20

Characteristics of bag 1 fibres

Answer 20

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

Question 21

Characteristics of bag 2

Answer 21

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

Question 22

Characteristics of chain fibres

Answer 22

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

Question 23

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

Answer 23

Ia afferents and II fibres

Question 24

What do Ia afferents form

Answer 24

A primary annulospial nerve ending

Question 25

What do II fibres form

Answer 25

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

Question 26

What do both types of afferent fibres respond to

Answer 26

Stretch

Question 27

What are Ia fibres more sensitive to

Answer 27

The rate of change of the intrafusal fibre

Question 28

What are II fibres more sensitive to

Answer 28

The absolute length of the intrafusal fibres

Question 29

Stimulation of the static gamma fibres causes

Answer 29

The static response to increase

Question 30

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

Answer 30

Only static gamma motor neurones

Question 31

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

Answer 31

Dynamic gamma motor neurones

Question 32

Where are the Golgi tendon organs located

Answer 32

The junction of the muscle and tendon

Question 33

What do the Golgi tendon organs monitor

Answer 33

The changes in muscle tension

Question 34

What are Golgi tendon organs in series with

Answer 34

Extrafusal fibres

Question 35

What innervates the Golgi tendon organs

Answer 35

Ib sensory afferents

Question 36

Characteristics of Ib afferents

Answer 36

Myelinated and slightly slower conducting than Iafibres

Question 37

Where do group Ib afferents synapse

Answer 37

Upon inhibitory interneurones

Question 38

What do the inhibitory interneurones synapse upon

Answer 38

The alpha motor neurones

Question 39

What forms the basis of the inverse myotatic reflex

Answer 39

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

Question 40

What is the polysnaptic pathway

Answer 40

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

Question 41

What does the inverse myotatic reflex protect

Answer 41

The muscle from overloading

Question 42

As muscle tension increases, what occurs

Answer 42

Inhibition of alpha motor neurones slows its contraction

Question 43

When muscle tension falls, what occurs

Answer 43

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

Question 44

Where are proprioceptive axons present

Answer 44

In connective tissue of joints

Question 45

What do proprioceptive axons respond to

Answer 45

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

Question 46

What do the proprioceptive axons prevent

Answer 46

Excessive flexion and extension

Question 47

What are proprioceptive axons made up of

Answer 47

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

Question 48

Where are free nerve endings found

Answer 48

In the capsule and connective tissue

Question 49

What type of proprioceptive axons are found within free nerve endings

Answer 49

High threshold and slow adapting receptors

Question 50

What is the role of receptors in free nerve endings

Answer 50

They have a protective role

Question 51

Paciniform endings are found where

Answer 51

In the periosteum

Question 52

What type of proprioceptive axons are found within the paciniform endings

Answer 52

Low threshold and slow adapting receptors

Question 53

What are the proprioceptive axon receptors in the paciniform

Answer 53

The are accelerated detectors

Question 54

Where are ruffini endings found

Answer 54

Mainly in joint capsules

Question 55

What type of proprioceptor axons are found in the ruffini endings

Answer 55

Low threshold and slow adapting

Question 56

What do the proprioceptor axons within the ruffini endings do

Answer 56

They monitor the static position and speed of movements

Question 57

Where do spinal interneurones receive input from

Answer 57

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

Question 58

What are the two types of interneurone input

Answer 58

Excitatory or inhibitory

Question 59

What do the inhibitory interneurones mediate

Answer 59

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

Question 60

What do the interneurones integrate

Answer 60

Incoming information to generate an output

Question 61

What are the two types of interneurones

Answer 61

Excitatory and inhibitory

Question 62

What does the myotatic reflex cause

Answer 62

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

Question 63

What is reciprocal inhibition important in

Answer 63

The inhibition of movement by the motor cortex

Question 64

What initiates the myotatic reflex

Answer 64

Voluntary contraction of an extensor muscle will stretch an antagonist flexor

Question 65

What do the excitatory interneurones mediate

Answer 65

The flexor reflex and crossed extensor reflex

Question 66

What happens in the flexor reflex

Answer 66

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

Question 67

What happens in the crossed extensor reflex

Answer 67

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

Question 68

What does the crossed extensor reflex enhance

Answer 68

Postural support during withdrawal of the foot from a painful stimulus