A nuclear bag fiber is a type of
intrafusal muscle fiber
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.Casagrand, Janet (2008) ''Action and Movement: Spinal Control o ...
that lies in the center of a
muscle spindle
Muscle spindles are stretch receptors within the body of a skeletal muscle that primarily detect changes in the length of the muscle. They convey length information to the central nervous system via afferent nerve fibers. This information can be ...
. Each has many
nuclei concentrated in bags and they cause excitation of the
primary sensory fibers.
There are two kinds of bag fibers based upon contraction speed and motor innervation.
#BAG2 fibers are the largest. They have no striations in middle region and swell to enclose nuclei, hence their name.
#BAG1 fibers, smaller than BAG2.
Both bag types extend beyond the spindle capsule.
These sense dynamic length of the muscle. They are sensitive to length and velocity.
See also
*
Nuclear chain fiber
A nuclear chain fiber is a specialized sensory organ contained within a muscle. Nuclear chain fibers are intrafusal fibers that, along with nuclear bag fibers, make up the muscle spindle responsible for the detection of changes in muscle len ...
References
External links
* http://www.unmc.edu/Physiology/Mann/mann11.html
Nervous system
Muscular system
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