Gammamotorneurones

Gamma motor neurons, also known as gamma motoneurons or small motor neurons, are a class of motor neurons originating in the spinal cord. They play a crucial role in regulating muscle tone and proprioception. Unlike alpha motor neurons, which innervate the extrafusal muscle fibers responsible for generating muscle force, gamma motor neurons innervate the intrafusal muscle fibers within muscle spindles. These intrafusal fibers are specialized sensory receptors that detect changes in muscle length.

The primary function of gamma motor neurons is to adjust the sensitivity of muscle spindles. When a gamma motor neuron is activated, it causes the intrafusal muscle fibers to contract. This contraction stretches the non-contractile central region of the muscle spindle, where the sensory afferent endings are located. By contracting the intrafusal fibers, gamma motor neurons ensure that the muscle spindle remains sensitive to changes in muscle length even when the main muscle is contracting. This mechanism is essential for maintaining muscle tone and for providing accurate feedback about limb position to the central nervous system.

There are two types of gamma motor neurons: static gamma motor neurons and dynamic gamma motor neurons. Static gamma motor neurons primarily influence the resting length of the muscle spindle, while dynamic gamma motor neurons are more involved in responding to rapid changes in muscle length. The activity of gamma motor neurons is modulated by descending pathways from the brain, allowing for voluntary control over muscle tone and proprioceptive feedback. Disruptions in gamma motor neuron function can lead to issues with muscle tone, coordination, and proprioception.