Question

Explain the mechanism of skeletal muscle stretch reflex, highlighting alpha-gamma co-activation and involved structures.

Answer 1

The stretch reflex is a muscle contraction in response to stretching within the muscle. A spinal reflex is a fast response that involves an afferent signal into the spinal cord and an efferent spinal out to the muscle.

When a muscle lengthens, the muscle spindle is stretched and its nerve activity increases. this increases alpha motor neuron activity, causing the muscle fiber contract and thus resist the stretching a secondary set of a neuron also causes the opposing muscle to relax. Gamma motoneurons regulate how sensitive the stretch reflex is by tightening or relaxing the fiber within the spindle. The several theories as to what may trigger gamma motoneurons to increase the reflex's sensitivity.

Alpha-gamma co-activation might keep the spindles taut when a muscle is contracted, preserving stretch reflex sensitivity even as the muscle fiber becomes shorter. Otherwise, the spindles would become slack and the relax would cease to function.

structure

the stretch reflex is accomplished through several different structures. In the muscle, there is muscle spindle, whose extrafusal muscle fibers lie parallel to the muscle and sense changes in length and velocity. the afferent sensory neuron is the structure that carries the signal from the muscle to the spinal cord.it carries this action potential to the dorsal root ganglion of the spinal cord. the efferent sensory neuron is the structure that carries the signal from the spinal cord back to the muscle. it carries the action potential from the ventral root of the spinal cord to the muscle down the alpha motor neuron.