The proprioceptor responsible for detecting muscle length is called:

The proprioceptor responsible for detecting muscle length is known as the muscle spindle. Muscle spindles are specialized sensory receptors located within the belly of muscles and are sensitive to stretch. When a muscle is stretched, the muscle spindles detect this change in length and send signals to the central nervous system regarding the muscle's current position and movement. This information is crucial for maintaining balance, coordinating movements, and providing feedback during activities that require precise control, such as dancing or playing sports.

Joint receptors, on the other hand, are primarily involved in detecting changes in the position and movement of joints, while the Golgi tendon organ is responsible for sensing tension in the tendons rather than length changes in muscles. Cutaneous receptors are related to sensations in the skin, such as touch, pressure, and temperature, and do not play a direct role in detecting muscle length. The specificity of the muscle spindle for this proprioceptive function makes it essential for motor control and proprioception.