One of two types of somatic motoneurons, and in fact the largest spinal motoneuron, which innervates extrafusal muscle fibers located throughout a muscle. In addition to voluntary skeletal muscle contraction, alpha motoneurons also play a role in muscle tone, the continuous force generated by non-contracting muscle to oppose stretching. When a muscle is stretched, sensory neurons within the muscle spindle detect the degree of stretch and send a signal to the CNS. The CNS activates alpha motoneurons in the spinal cord that cause extrafusal muscle fibers to contract and thereby resist further stretching. This process is also called the stretch reflex.
See Central nervous system (CNS), Corticospinal tract (CST), Direct corticospinal connections or tracts, Extrafusal muscle fibers, Gamma (g) motoneuron, Intrafusal muscle fibers, Motoneuron, Motor unit, Muscle spindle, Muscle tone (or power), Reflex, Ventral horn