Which mechanoreceptor responds to changes in muscle length?

• A. Golgi tendon organs
• B. Tendons
• C. Muscle spindles
• D. Proprioception

Answer: (C)

Muscle spindles, a type of proprioceptive receptor, respond to changes in muscle length. They’re built into the muscle and become stretched when the muscle lengthens, sending signals to the nervous system about how long the muscle is and how fast it’s changing length. This information helps regulate muscle tone and coordinate movement, including triggering protective reflexes if a muscle is stretched too quickly.

Golgi tendon organs sit at the junction of muscle and tendon and detect tension rather than length, helping prevent injury from excessive force. Tendons themselves are connective tissue, not receptors. Proprioception describes the sense of body position and movement, which relies on receptors like muscle spindles but isn’t itself a receptor. So the receptor that best fits “responds to changes in muscle length” is the muscle spindle.