A nuclear bag fiber is a type of intrafusal muscle fiber that lies in the center of a muscle spindle. Each has a large number of nuclei concentrated in bags and they cause excitation of both the primary and secondary nerve fibers.

There are 2 kinds of bag fibers based upon contraction speed and motor innervation. 1) Bag2 fibers - are the largest. They have no striations in middle region and swell to enclose nuclei (hence the word BAG!) 2) Bag1 fibers - are smaller than bag2.

Both bag types extend beyond the spindle capsule.

[edit] See also

• nuclear chain fiber.

[edit] External links

• http://www.unmc.edu/Physiology/Mann/mann11.html

This muscle article is a stub. You can help Wikipedia by expanding it. v • d • e

This neuroscience article is a stub. You can help Wikipedia by expanding it. v • d • e

v • d • e Nervous system, receptors: somatosensory system (GA 10.1059) Medial lemniscus Touch/mechanoreceptors: Pacinian corpuscles – vibration • Meissner's corpuscles – light touch • Merkel's discs – pressure • Ruffini endings - stretch • Free nerve endings – pain • Hair cells • Baroreceptor Proprioception: Golgi organ – tension/length • Muscle spindle – velocity of change (Intrafusal muscle fiber • Nuclear chain fiber • Nuclear bag fiber) Spinothalamic tract Pain: Nociception and Nociceptors Temperature: Thermoreceptors