Somatic Spinal Reflexes

There are three major somatic reflexes—the stretch reflex, the tendon reflex, and the flexor reflex.

The stretch reflex is a quick monosynaptic reflex that results in muscle contraction when the muscle is suddenly stretched.

Muscle spindles, muscle-specific sensory receptors, detect changes in muscle length and activate motor neurons that innervate the stretched muscle, causing it to contract.

The tendon reflex is a polysynaptic reflex that regulates muscle tension built during muscle contraction and prevents damage to the tendons.

Golgi tendon organs, sensory receptors in tendons, activate inhibitory interneurons to relax the tensed muscle. They can also activate excitatory motor neurons causing contraction of antagonistic muscles.

The flexor or withdrawal reflex leads to the withdrawal of a threatened body part from a painful stimulus.

A pain receptor detects the stimulus and, through a polysynaptic reflex arc, activates motor neurons that innervate the flexor muscles, causing them to contract.

The crossed-extensor reflex accompanies the flexor reflex and activates the extensor muscles in the opposite limb, allowing for balance and support.