In human skeletal muscle, what is the primary function of muscle spindles?

• A. Detect the position of joints by sensing pressure changes within synovial fluid
• B. Detect changes in muscle length (stretch) and the rate of stretch to help regulate muscle tone and reflexes
• C. Detect painful stimuli in muscle tissue and initiate withdrawal reflexes
• D. Detect changes in muscle tension at the tendon to prevent excessive force generation

Answer: (B)

Verified step by step guidance

1. Understand that muscle spindles are specialized sensory receptors located within skeletal muscles.
2. Recognize that their primary role is to monitor changes in muscle length, meaning they detect when a muscle is stretched.
3. Know that muscle spindles also sense the rate at which the muscle length changes, providing dynamic information about stretch speed.
4. Realize that this sensory input from muscle spindles is crucial for regulating muscle tone and initiating reflexes, such as the stretch reflex, which helps maintain posture and protect muscles from overstretching.
5. Differentiate muscle spindles from other sensory receptors: they do not detect joint position via synovial fluid pressure, pain stimuli, or tension at tendons (which is the role of Golgi tendon organs).