LMN Reflexes

Question 1

What are the 5 functional components of a reflex arc?

Answer 1

1) Stimulus eg. pain
2) AP along afferent spinal nerve
3) Integration centre within spinal cord - pass from sensory to motor
4) Motor neuron AP
5) Muscle/ gland responds

Question 2

In a myotactic stretch reflex, activation of the muscle spindle causes AP firing in what kind of nerve fibre?

Answer 2

1a afferent

Question 3

In the myotactic stretch reflex, contraction of the agonist muscle is a result of increased activity in which type of neuron?

Answer 3

Alpha motor neuron

Question 4

The myotactic stretch reflex requires 2 components, how many neurons is involved in each?

Answer 4

1) Contraction of agonist muscle (2 neurons - no interneuron)
2) Reciprocal inhibition of antagonist muscle groups (3 neurons requires an inhibitory interneuron)

Question 5

In reciprocal inhibition of the antagonist muscle groups during the myotatic reflex, what type of fibre is the interneuron?

Answer 5

1a inhibitory neuron

Question 6

The patellar tap reflex is an example of what kind of reflex?

Answer 6

Myotatic reflex

Question 7

The Golgi tendon reflex is an example of what kind of reflex?

Answer 7

Inverse myotatic reflex

Question 8

With increased muscle tension, Golgi tendon organ excitation causes increased firing in what king of neuron?

Answer 8

1b afferent

Question 9

How many neurons are involved in the inverse myotactic reflex?

Answer 9

3 - an inhibitory interneuron is involved

Question 10

Does the inverse myotatic reflex lead to contraction or relaxation of homonymous muscle (the one the signal came from)?

Answer 10

Relaxation - it is a protective mechanism

Question 11

The inverse myotatic reflex leads to decreased firing in what kind of nerve fibre via an interneuron?

Answer 11

alpha motor neuron fibre

Question 12

How does the inverse myotatic reflex affect antagonist muscle groups and how?

Answer 12

Contraction of antagonist muscle groups

Excitation of alpha motor neuron via an excitatory interneuron

Question 13

The myotatic stretch reflex and the inverse myotatic reflex are ipsilateral or contralateral?

Answer 13

Ipsilateral - all work on the same side from which the stimulus came

Question 14

What is the principle of the crossed extensor/ flexor withdrawal reflex?

Answer 14

Stimulus such as pain causes withdrawal on the ipsilateral side (flexion) and extension on contralateral side so don’t fall over

Question 15

In the crossed extensor/flexor withdrawal reflex, on activation of the cutaneous nociceptor there is increased activity in which 2 kinds of fibres?

Answer 15

A-delta and C afferents

Question 16

What is the effect on the ipsilateral flexors in the withdrawal reflex?

Answer 16

Polysynaptic activation of ipsilateral flexors (via excitatory interneuron)

Question 17

What is the effect on the ipsilateral extensors in the withdrawal reflex?

Answer 17

Polysynaptic inhibition of ipsilateral extensors (via an inhibitory interneuron)

Question 18

How many neurons are involved in the crossed extensor/ flexor withdrawal reflex to the contralateral side?

Answer 18

4 (2 interneurons)

Question 19

What is the effect on the contralateral extensors in the withdrawal reflex and how?

Answer 19

Polysynaptic excitation of the contralateral extensors via 2 excitatory interneurones

Question 20

What is the effect on the contralateral flexors in the withdrawal reflex and how?

Answer 20

Polysynaptic inhibition of the contralateral flexors via an excitatory neuron followed by an inhibitory neuron

Question 21

What type of fibre is the sensory afferent in the myotatic reflex?

Answer 21

1a

Question 22

What is the sensory stimulus in the myotatic reflex?

Answer 22

Change in muscle length

Question 23

What are the 3 proposed functions of the myotatic reflex?

Answer 23

1) Antigravity
2) Posture
3) Movement

Question 24

What type of fibre is the sensory afferent in the inverse myotatic reflex?

Answer 24

1b

Question 25

What is the sensory stimulus in the inverse myotatic reflex?

Answer 25

Change in muscle tension

Question 26

What are the 2 proposed functions of the inverse myotatic reflex?

Answer 26

1) Tension feedback

2) overload protection

Question 27

What is the sensory afferent in the flexor withdrawal reflex?

Answer 27

A delta and C fibres

Question 28

What is the sensory stimulus in the flexor withdrawal reflex?

Answer 28

Pain or damaging stimulus

Question 29

What are the 2 proposed functions of the withdrawal stimulus?

Answer 29

1) Damage limitation or avoidance

2) Maintained balance on limb withdrawal