Extrafusal muscle fiber

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Extrafusal muscle fiber
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Latin	myofibra extrafusalis
Gray's	subject #
System
MeSH	[1]
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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

External links

• Dorlands/Elsevier f_05/12360939
• Diagram at colorado.edu

Histology: muscle tissue

skeletal muscle/general: epimysium, fascicle, perimysium, endomysium, muscle fiber, myofibril

sarcomere (a, i, and h bands; z and m lines), myofilaments (thin filament/actin, thick filament/myosin, elastic filament/titin), tropomyosin, troponin

neuromuscular junction, intrafusal muscle fiber, extrafusal muscle fiber, motor unit, muscle spindle, sliding filament mechanism

myoblast, satellite cells, sarcoplasm, sarcolemma, sarcoplasmic reticulum, T-tubule

cardiac muscle: myocardium, intercalated disc

smooth muscle: calmodulin, vascular smooth muscle