Extrafusal muscle fiber

Extrafusal muscle fiber
Details
Identifiers
Latin	myofibra extrafusalis
TH	H3.03.00.0.00007
Anatomical terminology

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 sensory nerve endings in central noncontractile parts and by gamma motor neurons in contratile ends 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

References

• "Chapter 1: The Muscle Spindle and the Central Nervous System". Neuromuscular Reeducation with Electromyometric Feedback (PDF). Advanced Therapy Institute. Retrieved 30 November 2013.
• Smith, RS; Ovalle, Jr, WK (1973 October). "Varieties of fast and slow extrafusal muscle fibres in amphibian hind limb muscles". J Anat. 116 ((Pt 1)): 1–24. PMC 1271546. PMID 4273105‎. {{cite journal}}: Check |pmid= value (help); Check date values in: |date= (help)