Stretch reflex requires gamma motor neurons to set the length of the muscle. This reflex is a muscle contraction in response to the stretching of the muscle. It is a monosynaptic reflex which provides an autoregulation of skeletal muscle length. When this happens, the spindle of the muscle is stretched thus increasing its nerve activity.
The stretch reflex is caused by a muscle spindle stretch. When the stretch impulse is received a rapid succession of events follows. The motor neuron is then activated. This will contract the stretched muscled and its supporting muscles while it inhibits the antagonists muscles.