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
Depressor supercilii muscle Depressor supercilii muscle The depressor Supercilii is an eye muscle of the human body. The nature of this muscle is in some dispute. Few printed anatomies include it (Netter, et al.) and many authorities consider it to be part of the orbicularis oculi muscle. On the other hand, many dermatologists, ophthalmologists and plastic surgeons hold that the depressor supercilii is a distinct muscle and has a definite, individual effect on the movement of the eyebrow and skin of the glabella. The depressor supercilii originates on the medial orbital rim, near the lacrimal bone, and inserts on the medial aspect of