Extrafusal muscle fiber

Extrafusal muscle fiber is a term given to standard muscle fibers as to distinguish them from intrafusal muscle fibers. Extrafusal muscle fibers are innervated by alpha motor neurons and generate tension by contracting, thereby allowing for skeletal movement. Extrafusal muscle fibers are not to be confused with intrafusal muscle fibers which are innervated by gamma motor neurons and thus serve as a sensory proprioceptor.

The alpha motor neuron and the extrafusal muscle fibers it innervates make up the 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.

See also

• Intrafusal muscle fiber
• Type Ia sensory fiber
• Type II sensory fiber
• Alpha motor neuron
• Gamma motor neuron
• Beta motor neuron