Extrafusal muscle fiber

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

They generate tension, do 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.

[edit] External links

• f_05/12360939 at Dorland's Medical Dictionary
• Cartoon of intrafusal vs. extrafusal fibers

v • d • e Histology: muscle tissue skeletal muscle/general epimysium, fascicle, perimysium, endomysium, muscle fiber (intrafusal, extrafusal), myofibril sarcomere (a, i, and h bands; z and m lines), myofilaments (thin filament/actin, thick filament/myosin, elastic filament/titin, nebulin), tropomyosin, troponin (T, C, I) costamere (dystrophin, α,β-dystrobrevin, syncoilin, synemin/desmuslin, dysbindin, sarcoglycan, dystroglycan, sarcospan), desmin neuromuscular junction, motor unit, muscle spindle, excitation-contraction coupling, sliding filament mechanism myoblast, satellite cell, sarcoplasm, sarcolemma, sarcoplasmic reticulum, T-tubule cardiac muscle myocardium, intercalated disc, nebulette smooth muscle calmodulin, vascular smooth muscle