Intrafusal muscle fiber

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Intrafusal fibers are muscle fibers that comprise the muscle spindle. These fibers are walled off from the rest of the muscle by a collagen sheath. This sheath has a spindle or "fusiform" shape, hence the name "intrafusal." While the intrafusal fibers are wrapped with sensory receptors, their counterpart, extrafusal muscle fibers are the ones responsible for the power-generating component of muscle and are innervated by motor neurons.

It is by the sensory information from these two intrafusal fiber types that one is able to judge the position of their muscle, and the rate at which it is changing.

• Type Ia sensory fiber
• Type II sensory fiber

[edit] External links

• Histology at ucsd.edu
• Histology at umdnj.edu
• Cartoon of intrafusal vs. extrafusal fibers

v • d • e Nervous system, receptors: somatosensory system Medial lemniscus Touch/mechanoreceptors: Pacinian corpuscles – vibration • Meissner's corpuscles – light touch • Merkel's discs – pressure • Ruffini endings • Free nerve endings – pain • Hair cells • Baroreceptor Proprioception: Golgi organ – tension/length • Muscle spindle – velocity of change (Intrafusal muscle fiber • Nuclear chain fiber • Nuclear bag fiber) Spinothalamic tract Pain: Nociception and Nociceptors Temperature: Thermoreceptors

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