MUSCLE PHYSIOLOGY

Detailed explanation-1: -The spindles are stretched when the muscle lengthens. This stretch causes the sensory neuron in the spindle to transmit an impulse to the spinal cord, where it synapses with alpha motor neurons. This causes activation of motor neurons that innervate the muscle.

Detailed explanation-2: -When a muscle lengthens, the muscle spindle is stretched and its nerve activity increases. This increases alpha motor neuron activity, causing the muscle fibers to contract and thus resist the stretching. A secondary set of neurons also causes the opposing muscle to relax.

Detailed explanation-3: -The tap of the reflex hammer on the tendon stretches the muscle and therefore excites a volley of activity from the muscle spindles in the afferent axons. The afferent volley is relayed to the motor neurons in the brainstem or spinal cord, and an efferent volley returns to the muscle (see Figure 1.5).

Detailed explanation-4: -The stretch reflex or myotatic reflex refers to the contraction of a muscle in response to its passive stretching by increasing its contractility as long as the stretch is within physiological limits.