Reflexes

Question 1

What is a stretch reflex?

Answer 1

Muscle contraction in response to being stretched

Question 2

Why is a stretch reflex referred to as a monosynaptic reflex?

Answer 2

No interneurones involved

only one synapse

Question 3

Other than stretch reflexes, what other types of reflexes are monosynaptic?

Answer 3

None

It is the only known type

Question 4

An increased load is applied to a muscle, causing it to stretch. What will happen in terms of tension and length?

Answer 4

Stretch reflex causes further contraction ∴ increased tension

Muscle restores original length

Question 5

What neurones make the muscle ‘know’ that it is back to original length?

Answer 5

Gamma afferent neurones

Question 6

Describe the concept of reciprocal inhibition.

Answer 6

Agonist + antagonist muscles connect to a joint

Sensory fibres link directly to both

Excitatory signal sent to one muscle, whereas an inhibitory signal is sent to the other

One contracts, the other relaxes

Question 7

In terms of reciprocal inhibition, explain what happens when the patellar tendon is hit with a hammer (knee-jerk).

Answer 7

Stimulus on tendon ∴ afferent impulse to spinal cord

Diverges at spinal cord to 2 efferent neurones

1 efferent alpha goes to quad and stimulates contraction

1 efferent alpha goes to hamstring and causes it to relax

Question 8

What is responsible for causing the inverse stretch reflex?

Answer 8

Golgi tendon organs

Question 9

How does the inverse stretch reflex work when a muscle contracts and shortens?

Answer 9

Inhibitory agonist interneurones activated

Excitatory antagonist interneurones activated

Causes a collapse in resistance

Question 10

Flexor (withdrawal) reflex uses what type of receptors?

Answer 10

Pain receptors

Question 11

Describe how the flexor reflex is protective.

Answer 11

Withdraws part of the body away from painful stimulus

Question 12

In the flexor reflex, a single nociceptive pain receptor can trigger a massive response.

What feature of the circuitry of the reflex enables this?

Answer 12

A(gamma) nociceptive fibre branches a lot in the spinal cord

∴ activate interneurones in several spinal segments

∴ lots of Alpha motoneurons stimulate lots of flexor muscle fibres

Question 13

Why is the ‘contralateral limb’ extended when a flexor reflex is triggered?

Answer 13

Balance

Question 14

Which is slower, the flexor reflex or the stretch reflex?

Answer 14

Flexor

Nociceptive fibres have a much smaller diameter than muscle spindle afferents ∴ conduct slower