Spinal Reflexes

Question 1

What are the subdivisions of intrafusal fibres?

Answer 1

Nuclear bag fibres = bag 1 (dynamic), bag 2 (static)

Chain fibres

Question 2

What are the features of bag 1 fibres?

Answer 2

Very sensitive to rate of change of muscle length

Innervated by dynamic gamma motor neurons

Question 3

What are the features of bag 2 fibres?

Answer 3

More sensitive to absolute length of muscle

Innervated by static gamma motor neurons

Question 4

What are some features of chain fibres?

Answer 4

Sensitive to absolute length of muscle

Innervated by static gamma motor neurons

Question 5

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

Answer 5

Ia (Aalpha) fibres and II (Abeta) fibres

Question 6

How are Ia afferent fibres organised?

Answer 6

Form primary annulospinal nerve ending winding around the centre of all intrafusal fibres

Question 7

How are II afferent fibres organised?

Answer 7

Form flowerspray endings on all intrafusal fibres except bag 1 type = more slowly conducting

Question 8

Do both types of afferent fibres that innervate intrafusal fibres respond to stretch the same way?

Answer 8

No = Ia fibres are more sensitive to rate of change of stretch, whereas II fibres are more sensitive to absolute length of intrafusal fibres

Question 9

What does the Ia afferent fibre respond to?

Answer 9

Rate of change of muscle length and absolute length of the muscle

Question 10

What does stimulation of the static gamma motor neuron cause?

Answer 10

Increase of steady state

Question 11

What does stimulation of the dynamic gamma motor neuron cause?

Answer 11

Enhances the dynamic response of the Ia afferent fibre to stretch

Question 12

What are the only kind of activities that cause static gamma motor neurons to be active?

Answer 12

Activities in which muscle length changes slowly and predictably

Question 13

What behaviours cause dynamic gamma motor neurons to be active?

Answer 13

Behaviours in which muscle length changes rapidly and unpredictably

Question 14

What do dynamic and static gamma motor neurons form?

Answer 14

A fusimotor system

Question 15

Where are golgi tendon organs located?

Answer 15

At the junction of muscle and tendon = in series with extrafusal fibres

Question 16

What is the function of golgi tendon organs?

Answer 16

Monitor changes in muscle tension = act to regulate muscle tension to protect from overload and keep within optimal range

Question 17

What are golgi tendon organs innervated by?

Answer 17

Groub Ib sensory afferents = myelinated, slightly slower conducting than Ia fibres

Question 18

Where do group Ib afferents synpase once they enter the spinal cord?

Answer 18

Upon inhibitory interneurons which in turn synapse upon alpha motor neuorns of the homonymous muscle = forms basis of reverse myotatic reflex

Question 19

What does the reverse myotatic reflex involve?

Answer 19

Polysynaptic pathway = inhibitory neuron is interposed between the Ib afferent and alpha motor neuron

Question 20

What is the reverse myotatic reflex important in?

Answer 20

Execution of fine motor acts

Question 21

Where are proprioceptive axons located?

Answer 21

In the connective tissue of joints

Question 22

What do proprioceptive axons respond to?

Answer 22

Changes in angle, direction and velocity of movement of a joint = also prevent excessive flexion or extension

Question 23

What are proprioceptive axons a mix of?

Answer 23

Fast adapting and slowly adapting units that have either high threshold or low threshold for activation

Question 24

What are examples of endings of proprioceptive axons?

Answer 24

Free nerve endings, golgi type endings, Paciniform endings, Ruffini endings

Question 25

What are some features of free nerve endings of proprioceptive axons?

Answer 25

Found in capsule and connective tissue Most numerous High threshold and slowly adapting Nocicepetive function

Question 26

What are some features of golgi type endings of proprioceptive axons?

Answer 26

Found only in ligaments High threshold and slowly adapting Protective role

Question 27

What are some features of Paciniform endings on proprioceptive axons?

Answer 27

Found in periosteum near articular attachments and fibrous part of joint capsule Low threshold and slowly adapting Acceleration detectors

Question 28

What are some features of Ruffini endings on proprioceptive axons?

Answer 28

Found mainly in joint capsule Low threshold and slowly adapting Static position and speed of movements

Question 29

Where does proprioceptive info arise from?

Answer 29

Muscle spindles, golgi tendon organs and joint receptors

Question 30

Where do spinal interneurons receive input from?

Answer 30

Primary sensory axons, descending axons from the brain, collaterals of LMN and other interneurons

Question 31

What types of input can spinal interneurons receive?

Answer 31

Excitatory or inhibitory

Question 32

What is the function of spinal interneurons?

Answer 32

Integrate incoming info to generate an output

Question 33

What is the function of inhibitory interneurons?

Answer 33

Mediate inverse myotatic response and reciprocal inhibition between extensor and flexor muscles

Question 34

What is the myotatic reflex an example of?

Answer 34

Reciprocal inhibition

Question 35

What occurs in the myotatic reflex?

Answer 35

Causes homonymous extensor muscle to contract but also causes simultaneous relaxation of antagonist flexor muscle

Question 36

What is the innervation of the myotatic reflex?

Answer 36

Ia afferent from muscle spindle extensor makes excitatory monosynaptic contact with alpha motor neuron innervating the homonymous muscle

Question 37

How does the Ia afferent fibre inhibit the alpha motor neuron that supplies the flexor muscle in the myotatic reflex?

Answer 37

Via polysynaptic pathways involving interneurons

Question 38

What is reciprocal inhibition important in?

Answer 38

Initiation of movement by the motor cortex

Question 39

What do excitatory interneurons mediate?

Answer 39

The flexor reflex and crossed extensor reflex

Question 40

What is the flexor reflex?

Answer 40

Noxious stimulus causes limb to flex by contraction of flexor muscles via exicitatory interneurons, and relaxation of extensor muscles via excitatory and inhibitory interneurons

Question 41

What is the crossed extensor reflex?

Answer 41

Noxious stimulus causes limb to extend by contraction of extensor muscles via excitatory interneurons, and relaxation of flexor muscles via excitatory and inhibitory interneurons

Question 42

What does the crossed extensor reflex enhance?

Answer 42

Postural support during withdrawl of a body part from painful stimulus