fusimotoriska

Fusimotoriska refers to the efferent innervation of muscle spindles, which are sensory receptors found within skeletal muscles. Muscle spindles are responsible for detecting changes in muscle length and the velocity of those changes. The fusimotor system, also known as the gamma motor system, consists of gamma motor neurons that originate in the spinal cord and project to specialized muscle fibers within the muscle spindle called intrafusal fibers.

Activation of gamma motor neurons causes the intrafusal fibers to contract. This contraction serves to adjust the sensitivity of the muscle spindle to stretch. By altering the tension of the intrafusal fibers, the fusimotor system can fine-tune the muscle spindle's ability to report changes in overall muscle length. This is crucial for maintaining precise control over muscle movements, posture, and reflexes. For instance, if a muscle is stretched, the muscle spindle sends a signal to the central nervous system, which can then trigger a reflex contraction to oppose the stretch. The fusimotor system modulates this reflex by ensuring the spindle remains responsive even when the main muscle is shortened. Without this precise control, muscle movements would be jerky and less accurate.