A muscle spindle, with γ motor and Ia sensory fibres

Intrafusal muscle fibres are skeletal muscle fibres that comprise the muscle spindle and are innervated by gamma motor neurons. These fibres are a proprioceptor that detect the amount and rate of change of length in a muscle.^[1] 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."

Intrafusal muscle fibres are not to be confused with extrafusal muscle fibres, which are innervated by alpha motor neurons and contract, generating skeletal movement.

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

[edit] See also

• Extrafusal muscle fibre

• Type Ia sensory fibre

• Type II sensory fibre

[edit] References

[edit] External links

• Histology at ucsd.edu
• Histology at umdnj.edu

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