Lihasspindeli

Lihasspindeli, 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. Muscle spindles are specialized stretch receptors that detect changes in muscle length and the rate of change of muscle length.

Each muscle spindle contains several small, specialized muscle fibers called intrafusal fibers. These fibers are innervated by both sensory and motor neurons. The sensory neurons, known as Ia afferents, are responsible for transmitting information about muscle stretch to the central nervous system. The motor neurons, called gamma motor neurons, innervate the intrafusal fibers and can alter their sensitivity to stretch.

When a muscle is stretched, the intrafusal fibers within the muscle spindle are also stretched. This stretching activates the Ia afferent neurons, sending signals to the spinal cord and brain. In response to this sensory input, a reflex arc can be triggered, causing the muscle to contract, a phenomenon known as the stretch reflex. This reflex is essential for maintaining posture, balance, and for rapid, involuntary adjustments during movement.

Muscle spindles are distributed throughout most skeletal muscles, with a higher density found in muscles responsible for fine motor control, such as those in the hands and face. Their continuous monitoring of muscle length and tension allows for precise and coordinated muscle activity, contributing to smooth and controlled movements. Damage or dysfunction of muscle spindles can lead to problems with coordination, balance, and proprioception.