Group Fitness Instructor

Answer: D - A motor unit is defined as an alpha motor neuron and all the muscle fibers it innervates. Alpha motor neurons innervate extrafusal fibers, the highly contracting fibers that give each muscle power. In contrast, gamma motor neurons innervate intrafusal muscle fibers (for example, muscle spindles). The function of intrafusal muscle fibers is not to provide force to the muscle; rather, their job is to keep the muscle taut so that it is highly reactive to stretch, no matter what degree of muscle elongation.