Muscle spindles are specialized sensory receptors located within skeletal muscles. They detect changes in muscle length and the rate of that change, providing essential information about muscle stretch and tension. This feedback helps the body maintain balance and posture during movement. These structures consist of a bundle of intrafusal muscle fibers surrounded by a capsule. When a muscle stretches, the spindles send signals to the central nervous system, which processes the information and can trigger reflex actions to adjust muscle activity, ensuring smooth and coordinated movements.