Extrafusal muscle fiber

Extrafusal muscle fibers are a class of muscle fiber innervated by alpha motor neurons.

They are motor neurons and generate tension, mechanical work and allow for movement by contracting.

Compare with intrafusal muscle fiber - is of sensory type and innervated by gamma motor neurons.

Extrafusal muscle fibers and associated alpha motor neurons are called a motor unit. The connection between alpha motor neuron and extrafusal muscle fiber is a neuromuscular junction, and the neurotransmitter responsible for contraction is acetylcholine.