What is muscle spindle ?« Back to Questions List

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Posted by Tarik Paik
Asked on December 5, 2018 2:06 pm
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It essentially consist of modified muscle fibres called intrafusal fibries. The end of these fibries are striated and inverted by γ – motor neurons.
These are again two types – (i) nuclear bag fibers which has a bulged central part of a nuclear more concentrated. (ii) Nuclear chain fibers which are of uniform diameter and nuclei distributed uniformly.

I A afferent fibers innervate the central part of these fibers ( annulospiral ending ).
The peripheral parts are inverted by Gr-II afferent with flower- spray endings.
When the muscle in streached, it is stimulated. Afferent impulse is generated in the afferent ending s. It travels along the afferent and reach the α – motor neurone in the spinal cord.

The motor neurone is excited. The impulse passes out via the axons of these neurones and reach the neuro-muscular junction ,in the extrafusal fibers . The muscle fibres are excited by the release of neurotransmitter,acetylcholine. Muscle action potential develops. It excites the muscle and muscle contracts.

Posted by aalkhadiza
Answered On December 5, 2018 2:32 pm