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Intrafusal muscle fiber

Skeletal muscle fibers

Skeletal muscle fibers

FieldValue
NameIntrafusal muscle fiber
Latinmyofibra intrafusalis
ImageMuscleSpindle.svg
CaptionA muscle spindle, with γ motor and Ia sensory fibers
FunctionProprioception
PartOfSkeletal muscle

Intrafusal muscle fibers are skeletal muscle fibers that serve as specialized sensory organs (proprioceptors). They detect the amount and rate of change in length of a muscle. They constitute the muscle spindle, and are innervated by both sensory (afferent) and motor (efferent) fibers.

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

Structure

Types

There are two types of intrafusal muscle fibers: nuclear bag fibers and nuclear chain fibers. They bear two types of sensory ending, known as annulospiral and flower-spray endings. Both ends of these fibers contract, but the central region only stretches and does not contract.

Intrafusal muscle fibers are walled off from the rest of the muscle by an outer connective tissue sheath consisting of flattened fibroblasts and collagen. This sheath has a spindle or "fusiform" shape, hence the name "intrafusal".

Innervation

They are innervated by gamma motor neurons and beta motor neurons. Gamma efferents from small multipolar neurons from anterior gray column innervate it. These form a part of neuromuscular spindles.

Function

Intrafusal muscle fibers detect the amount and rate of change in muscle length. It is by the sensory information from gamma motor neurons and beta motor neurons that an individual is able to judge the position of their muscles.

References

References

  1. Falkel, LORI. (2007-01-01). "Chapter 4 - Tissue-Specific Exercises for the Upper Extremity". Mosby.
  2. Casagrand, Janet (2008) ''Action and Movement: Spinal Control of Motor Units and Spinal Reflexes.'' University of Colorado, Boulder.
  3. Burke, David. (2014-01-01). "Fusimotor System". Elsevier.
  4. Johns, Paul. (2014-01-01). "Chapter 4 - Sensory and motor pathways". Churchill Livingstone.
  5. (2011). "Gray's Clinical Neuroanatomy: The Anatomic Basis for Clinical Neuroscience". Elsevier Saunders.
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This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page.

muscular-system
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