Question

In the muscle spindle, the intrafusal fiber is composed of three parts. The first part is ____, the second part is ____, and the third part is ____. The DRG _____ portion surrounds the _____ part of the intrafusal fiber. The non-contractile part is deformed by contraction.

Answer 1

The muscle spindle's intrafusal fibers are composed of nuclear bag fibers, nuclear chain fibers, and a non-contractile axial region. The sensory portion of the dorsal root ganglion neuron wraps around the non-contractile part and conveys information about muscle stretch.

Step-by-step explanation:

The muscle spindle is a sensory receptor within the muscle that is sensitive to changes in muscle length and the rate of that change. The intrafusal fibers within the muscle spindle are composed of three parts: the nuclear bag fibers, the nuclear chain fibers, and the axial region, which is non-contractile. The dorsal root ganglion (DRG) neuron's sensory portion surrounds the middle, non-contractile part of the intrafusal fiber. When a muscle contracts, it can deform the non-contractile central portion, thereby activating the sensory neuron to send information about muscle stretch to the central nervous system.