Nuclear bag fiber
A nuclear bag fiber is a type of intrafusal muscle fiber that lies in the center of a muscle spindle. Each has many nuclei concentrated in bags and they cause excitation of both the primary and secondary nerve fibers.
|Nuclear bag fiber|
|Anatomical terms of microanatomy|
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.
- Boyd, I A; Gladden, M H; McWilliam, P N; Ward, J (February 1977). "Control of dynamic and static nuclear bag fibres and nuclear chain fibres by gamma and beta axons in isolated cat muscle spindels". Journal of Physiology. 265 (1): 133–162. doi:10.1113/jphysiol.1977.sp011709. PMC 1307812. PMID 139469.