Intrafusal muscle fiber

Intrafusal muscle fiber
A muscle spindle, with γ motor and Ia sensory fibers
Latin	myofibra intrafusalis
Code	TH H3.03.00.0.00012

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

There are two types of intrafusal muscle fibers: nuclear bag and nuclear chain fibers. They bear two types of sensory ending, known as annulospiral and flower-spray endings.

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

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.

See also

• Alpha motor neuron
• Beta motor neuron
• Extrafusal muscle fiber
• Gamma motor neuron
• Type Ia sensory fiber
• Type II sensory fiber

References

External links

• Histology at ucsd.edu
• Histology at umdnj.edu
• "Chapter 1: The Muscle Spindle and the Central Nervous System". Neuromuscular Reeducation with Electromyometric Feedback. Advanced Therapy Institute. Retrieved 30 November 2013.