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Gamma motor neuron
Gamma motor neurons (γ motor neurons), also called gamma motoneurons, are a type of lower motor neuron that take part in the process of muscle contraction, and represent about 30% of fibers going to the muscle.〔Hunt, C. (1951) "The reflex activity of mammalian small-nerve fibres." Journal of Physiology. 115(4): 456–469.〕 Like alpha motor neurons, their cell bodies are located in the anterior horn of the spinal cord. They receive input from the bulboreticular facilitatory region of the pons in the brainstem. Their axons are smaller than alpha motor neurons, with a diameter of only 5 μm. Unlike the alpha motor neurons, gamma motor neurons do not directly adjust the lengthening or shortening of muscles. However, their role is important in keeping muscle spindles taut, thereby allowing the firing of alpha neurons to continue discharging, leading to muscle contraction. These neurons also play a role in adjusting the sensitivity of muscle spindles.〔Burke, D., Skuse, N.F., Stuart, D.G. (1979) "The regularity of muscle spindle discharge in man." Journal of Physiology. 291: 277–290〕
The presence of myelination in γ motor neurons allows a conduction velocity of 4 to 24 meters per second, significantly faster than with non-myelinated axons〔Andrew BL, Part NJ (1972) Properties of fast and slow motor units in hind limb and tail muscles of the rat. Q J Exp Physiol Cogn Med Sci 57:213-225.〕〔Russell NJ (1980) Axonal conduction velocity changes following muscle tenotomy or deafferentation during development in the rat. J Physiol 298:347-360.〕 but slower than in alpha motor neurons.
== General background of muscles ==
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