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In the nervous system, gamma motor neurons (γ-MNs) are slow-conducting lower motor neurons that innervate intrafusal muscle fibers. They form part of the reflex circuit that underlies muscle spindles and are therefore an integral part of the sense of body position. These neurons synapse on the poles of the muscle spindles and cause contraction of the spindles so that they remain taut when the surrounding extrafusal fibers have contracted and would otherwise relieve tension on the spindles. This ensures the muscle's stretch reflex is always active. Gamma motor neuron activity also regulates how strongly the muscle responds to a given amount of stretch, thus allowing small changes in muscle length to cause large changes in muscle force.
