Nuclear bag fibres are related to:
Ans. d. Length and velocity (Ref: Ganong 23/e p158; Guyton and Hall 11/e p.673- 76)Nuclear bag fibres are related to length and velocity.Dynamic nuclear bag fibers are highly sensitive to the rate of change in muscle length, providing velocity sensitivity to muscle stretch."Nuclear bag fibers can be divided into nuclear bag fibers type I and nuclear bag fiber type 2. The sum of these difference renders: (1) the nuclear bag type 1 fibers with little elasticity in their polar regions making them sensitive to dynamic changes (velocity of length change); and (2) nuclear bag type 2 with significant elasticity in their polar region making them sensitive to the changes in length (but not to the velocity of length change). Hence, nuclear bag fibers type I are also called dynamic nuclear bag fibers and nuclear bag fibers type II fibers are also called static nuclear bag fibers"- http ://pediatricneuro. com/alfonso/tip%20muscIe%20spindle.htmMuscle SpindleIt is 3- 12 mm tong structure consisting of 3-12 very small intrafusal muscle fibers, enclosed in a connective tissue capsule.Intrafusal fibers are more embryonal in character and have less distinct striations than the rest of fibers (extrafusal fibers) in the muscle.Muscle spindle acts through muscle stretch reflexQ.Muscle SpindleTypes of intrafusal fiber* Central (mid) part of fibers has few or no action and myosin filaments, so the ends of intrafusal fibers are contractile, whereas central portions probably are notQ* It's central portion functions as sensory receptor* Two types of intrafusal fibers are:* Primary ending is exerted by both nuclear bag and nuclear chain fibers.Sensory nerve endings* Central sensory receptor portion of muscle spindle is stimulated by stretching of midportion either by lengthening of whole muscle or even by contraction of end portion of intrafusal fibers.* Two type of sensory nerve endings areNuclear Bag FibersNuclear Chain FibersPrimary annulospiral endingsSecondary flower spray endings* Typically 2 (1-3) bag fibers occurs per spindle.* Nuclear bag fiber 1 with low level of myosin ATPase activity and nuclear bag fiber 2 with high level of myosin ATPase activityQ.* 3-9 fibers per spindle* Shorter and thinnerQ (about half) as compared to bag fibers* Nuclei are arranged in a chain throughout receptor area* Secondary ending is excited only by nuclear chain fibers* Are terminations of rapidly conducting (70-120 m/s) 17 m diameter group la afferent fibersQ.* It wraps (encircles) the central position of nuclear bag and nuclear chain fibersQ.* When the length of spindle receptor increases suddenly (i.e., dynamic response to rate of change of receptor length), only primary endings are stimulatedQ* Are terminations of group II sensory fibersQ (8 m diameter)* Located near the ends but only on nuclear chain fibersQ* May encircle fiber but usually it spreads like branches on a bush.
Force
Length
Tone
Length and velocity
Nerve Physiology