What structure detects force exerted by the muscle?

The Golgi tendon organ is a sensory receptor located at the junction of muscles and tendons, and it plays a critical role in detecting the force exerted by the muscle during contraction. Specifically, it senses changes in muscle tension or load, and when the muscle exerts force, the Golgi tendon organ becomes activated. This structure provides essential feedback to the central nervous system to help regulate muscle activity, prevent injury, and maintain optimal performance.

Muscle spindles, another type of sensory receptor, are primarily responsible for detecting changes in muscle length and the rate of that change (i.e., stretch), rather than force. Alpha motor neurons play a critical role in muscle contraction by transmitting signals from the nervous system to the muscle fibers, but they do not detect forces. Joint receptors are involved in sensing changes in joint position and movement, but they also do not specifically detect the force exerted by muscles. Thus, the Golgi tendon organ is uniquely designed for force detection, making it the correct answer in this context.