Basic Stretch Reflex

Question 1

What is the stretch reflex?

Answer 1

An automatic muscle contraction that occurs in response to muscle stretch to maintain muscle length and posture.

Question 2

Why is the stretch reflex important?

Answer 2

It helps maintain posture, muscle tone, and joint stability, and protects muscles from overstretching.

Question 3

What receptor detects muscle stretch?

Answer 3

The muscle spindle.

Question 4

Where are muscle spindles located?

Answer 4

Within the muscle belly, arranged in parallel with muscle fibres.

Question 5

What happens when a muscle is stretched?

Answer 5

Muscle spindles are activated and send sensory signals to the spinal cord.

Question 6

Which type of sensory neuron carries stretch information?

Answer 6

Ia afferent sensory neurons.

Question 7

Where does the stretch reflex integrate?

Answer 7

In the spinal cord.

Question 8

Is the stretch reflex monosynaptic or polysynaptic?

Answer 8

Monosynaptic for the agonist muscle.

Question 9

What happens to the agonist muscle during the stretch reflex?

Answer 9

It contracts to resist the stretch.

Question 10

Which neuron activates the agonist muscle?

Answer 10

Alpha motor neuron.

Question 11

What happens to the antagonist muscle during the stretch reflex?

Answer 11

It relaxes.

Question 12

What mechanism causes relaxation of the antagonist muscle?

Answer 12

Reciprocal inhibition via inhibitory interneurons.

Question 13

Why is reciprocal inhibition important?

Answer 13

It allows smooth and efficient movement by preventing opposing muscle contraction.

Question 14

What is an example of the stretch reflex in clinical testing?

Answer 14

The patellar (knee jerk) reflex.

Question 15

What does an exaggerated stretch reflex suggest?

Answer 15

Upper motor neuron (UMN) lesion.

Question 16

What does a reduced or absent stretch reflex suggest?

Answer 16

Lower motor neuron (LMN) lesion or peripheral neuropathy.

Question 17

How does the brain influence the stretch reflex?

Answer 17

Descending pathways modulate reflex excitability.

Question 18

Why is the stretch reflex clinically relevant in stroke?

Answer 18

Loss of inhibitory control can lead to hyperreflexia and spasticity.

Question 19

What role does the stretch reflex play in spasticity?

Answer 19

Increased reflex excitability causes velocity-dependent resistance to stretch.

Question 20

Is the stretch reflex voluntary?

Answer 20

No, it is involuntary and automatic.