Extrafusal muscle fiber Extrafusal muscle fiber Extrafusal muscle fibers are the skeletal standard muscle fibers that are innervated by alpha motor neurons and generate tension by contracting, thereby allowing for skeletal movement. They make up the large mass of skeletal muscle tissue and are attached to bone by fibrous tissue extensions (tendons). Each alpha motor neuron and the extrafusal muscle fibers innervated by it make up a motor unit. The connection between the alpha motor neuron and the extrafusal muscle fiber is a neuromuscular junction, where the neuron's signal, the action potential, is transduced to the muscle fiber by the neurotransmitter acetylcholine. Extrafusal
Skeletal muscle "flexor" and "extensor"; "abductor" and "adductor"; "levator" and "depressor"; "supinator" and "pronator"; "sphincter", "tensor", and "rotator" muscles. A flexor muscle decreases the anterior angle at a joint; an extensor increases the anterior angle at a joint. An abductor moves a bone away from the midline; an adductor moves a bone closer to the midline. A levator raises a structure; a depressor moves a structure down. A supinator turns the palm of the hand up; a pronator turns the palm down. A sphincter decreases the size of an opening; a tensor tenses a body part; a rotator turns a bone around