Muscle Spindle

**The muscle spindle** is a neuromuscular mechanism for regulating muscle tension present in the skeletal muscles of humans and other vertebrates. It is one of the key elements of the neuromuscular system, playing a role in the innervation and control of skeletal muscles.

Muscle spindles are a chain of contracted muscle cells located next to each other and between which there are sarcoplasms of smooth muscle joints. Each spindle muscle cell contains three types of muscle fibers: α, β and γ. α fibers are located closer to the center of the cell, β fibers are located towards the periphery, and γ fibers are located at the edges of the spindle. Alpha fibers are equipped with nerve endings that can excite muscle cells when they are activated.

Normally, muscle spindle fibers are not stimulated spontaneously, but when the muscle relaxes, they are stimulated by stretch at a fixed length of the muscle. As a result, each spindle fiber begins to contract, counteracting the stretch of the muscle and putting it under tension. If a muscle is under tension, the tubules in the spindle fibers excite the motor neurons responsible for innervating that muscle, thereby increasing the excitation of the motor neurons and giving a “warning” to the muscle to contract. In general, the muscle spindle functions to control muscle tension and contraction by detecting stretch in the muscle and triggering a contraction signal. When activated, the muscles become more sensitive to stimuli and can contract very quickly, which is useful for exercise using the fusiform system.