Intrafusal muscle fibers

Intrafusal muscle fibers are specialized muscle fibers found within a muscle spindle. They play a crucial role in the sensory system, providing the central nervous system with information about the degree of muscle length and changes in muscle length.

Structure

Intrafusal muscle fibers are smaller than the regular (extrafusal) muscle fibers. They are enveloped by a capsule that separates them from the rest of the muscle. Each muscle spindle contains several intrafusal muscle fibers, which can be classified into two types: nuclear bag fibers and nuclear chain fibers.

Nuclear bag fibers

Nuclear bag fibers are one type of intrafusal muscle fiber. They are called 'bag' fibers because their nuclei are clustered in bags. These fibers are sensitive to the rate of change in muscle length.

Nuclear chain fibers

Nuclear chain fibers are the other type of intrafusal muscle fiber. They are called 'chain' fibers because their nuclei are arranged in a chain-like manner. These fibers are sensitive to the absolute muscle length.

Function

Intrafusal muscle fibers play a key role in proprioception, which is the sense of the relative position of one's own parts of the body and strength of effort being employed in movement. They provide the central nervous system with information about muscle length and changes in muscle length, which is essential for coordinating muscle activity and maintaining posture.

Clinical significance

Abnormalities in intrafusal muscle fibers can lead to a variety of neurological disorders, including muscle spasticity, muscle weakness, and impaired proprioception.

See also

• Muscle spindle
• Proprioception
• Muscle fiber
• Central nervous system

References

Intrafusal muscle fibers Resources
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