Nuclear chain fiber
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2007-10-17T19:22:57Z
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Reverted 1 edit by [[Special:Contributions/SwiftGus|SwiftGus]] identified as [[WP:VAND|vandalism]] to last revision by [[User:Rjwilmsi|Rjwilmsi]]. using [[WP:TW|TW]]
[[Image:MuscleSpindle.svg|right|264px|thumbnail|A muscle spindle, with γ motor and Ia sensory fibers]]
A '''Nuclear chain fiber''' is a specialized [[Sensory receptor|sensory]] [[organ (anatomy)|organ]] contained within a [[muscle]]. '''Nuclear chain fibers''' are [[intrafusal]] fibers which, along with [[nuclear bag fiber]]s, make up the [[muscle spindle]] responsible for the detection of changes in muscle length.
There are 3-9 '''nuclear chain fibers''' per muscle spindle that are half the size of the [[nuclear bag fiber]]s. Their nuclei are aligned in a chain and they excite the secondary nerve. They are static while the nuclear bag fibers are dynamic in comparison. The name "nuclear chain" refers to the structure of the central region of the fiber, where the sensory axons wrap around the intrafusal fibers.
The secondary nerve association involves an efferent and afferent pathway that measure the stress and strain placed on the muscle (usually the [[extrafusa]]l fibers connected from the muscle portion to a bone). The afferent pathway resembles a spring wrapping around the nuclear chain fiber and connecting to one of its ends away from the bone. Again, depending on the stress and strain the muscles sustains, this afferent and efferent coordination will measure the "stretch of the spring" and communicate the results to the [[central nervous system]].
Also note that a similar structure attaching one end to muscle and the other end to a tendon is known as a [[Golgi tendon]]. However, golgi tendons differ from nuclear chain and [[nuclear bag fibers]] in that they are considered [[series and parallel circuits#Series circuits|in series]] rather than [[series and parallel circuits#Parallel circuits|in parallel]] to the muscle fibers.
==Innervation==
As [[intrafusal]] muscle fibers, '''nuclear chain fibers''' both send [[afferent]] innvervation and receive [[efferent]] innervation. The afferent innervation is via Group II and Ia neruons. These project to the [[nucleus proprius]] in the [[dorsal horn]] of the [[spinal cord]]. Efferent innervation is via [[Gamma motoneurons|static γ nerons]]. Stimulation of γ neurons causes the nuclear chain to shorten along with the [[extrafusal]] muscle fibers. This shortening allows the nuclear chain fiber to be sensitive to changes in length while its corresponding muscle is flexed.
==External links==
* http://www.unmc.edu/Physiology/Mann/mann11.html
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[[Category:Nervous system]]
[[Category:Muscular system]]
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