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
Frontalis muscle paler in color. It is located on the front of the head. The muscle has no bony attachments. Its medial fibers are continuous with those of the procerus; its immediate fibers blend with the corrugator and orbicularis oculi muscles, thus attached to the skin of the eyebrows; and its lateral fibers are also blended with the latter muscle over the zygomatic process of the frontal bone. From these attachments the fibers are directed upward, and join the galea aponeurotica below the coronal suture. The medial margins of the frontalis muscles are joined together for some distance above the root of