Final answer:
A stretch reflex is a type of reflex that occurs when a skeletal muscle is stretched. It helps to maintain muscles at a constant length and prevent over-stretching or over-contraction of muscles.
Step-by-step explanation:
A stretch reflex is a type of reflex that occurs when a skeletal muscle is stretched. When the muscle is stretched, sensory neurons called muscle spindles increase their rate of firing. This increase in firing causes the muscle to contract, which relieves the stretch. This reflex is useful because it helps to maintain muscles at a constant length. It prevents over-stretching of muscles, which can lead to tearing. It also helps to prevent over-contraction of muscles, ensuring that they can function properly without becoming too tense or rigid.