A muscle spindle is a sensory receptor located within skeletal muscles. It detects changes in muscle length and the rate of that change, helping the body maintain balance and posture. Muscle spindles are composed of specialized muscle fibers called intrafusal fibers, which are surrounded by a capsule. When a muscle stretches, the muscle spindle sends signals to the nervous system, informing it about the degree of stretch. This information is crucial for coordinating movements and preventing injury. The central nervous system processes these signals to adjust muscle contractions accordingly, ensuring smooth and controlled motion.