M1TI Osteopathic Manipulative Medicine (OMM) Practice Test

Where are the contractile regions of intrafusal fibers located?

At the center of the fiber. In the ends of the fiber. Throughout the fiber length equally. Not contractile at all.

Correct Answer:

In the ends of the fiber.

Explanation:

Intrafusal fibers within a muscle spindle are arranged with a noncontractile central region that houses the sensory endings, while the contractile elements are located at the ends (poles) of the fiber. Gamma motor neurons tighten these polar regions, adjusting spindle sensitivity as the muscle length changes. Because the center is noncontractile and the ends contain the contractile machinery, the contractile regions are at the ends of the intrafusal fiber.

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