Where are muscle spindles located?

• A. In tendon
• B. In synovial capsule
• C. In bone
• D. In muscle belly

Answer: (D)

Muscle spindles are sensory receptors embedded within skeletal muscle and detect changes in muscle length and the speed of stretch. They are located inside the muscle belly as intrafusal fibers arranged in parallel with the normal, or extrafusal, muscle fibers. This placement lets them continuously monitor how much the muscle is lengthening during movement and contribute to the stretch reflex and motor control. They are not located in tendons, bones, or the synovial capsule—the tendon houses Golgi tendon organs, and the joint capsule has its own sensory receptors—whereas muscle spindles reside within the muscle tissue itself, throughout the muscle belly.