lihasspindelissä

Lihasspindelissä, also known as muscle spindle, is a sensory receptor found in skeletal muscles. It plays a crucial role in proprioception, the sense of the relative position of one's own parts of the body and strength of effort being employed in movement. These specialized muscle fibers are enclosed within a connective tissue capsule.

There are two main types of sensory endings associated with muscle spindles: primary afferents and secondary afferents. Primary afferents, originating from Type Ia nerve fibers, are sensitive to changes in muscle length and the rate of change. Secondary afferents, from Type II nerve fibers, are primarily responsive to static muscle length.

The muscle spindle's structure allows it to detect and signal the stretch of the surrounding muscle. When a muscle is stretched, the spindle also stretches, activating the sensory neurons. This activation triggers a reflex arc, leading to a contraction of the same muscle (myotatic reflex) to resist the stretch. This mechanism is vital for maintaining posture, balance, and smooth, coordinated movements.

Muscle spindles are also involved in sensing effort. By monitoring the degree of stretch and the resulting muscle contraction, the nervous system can gauge the amount of force being generated. This information is processed in the brain to refine motor commands and adapt movements to changing conditions. Damage or dysfunction of muscle spindles can lead to impaired coordination, muscle weakness, and abnormal reflexes.