The Golgi tendon reflex (also called negative or inverse stretch reflex) is a bisynaptic reflex, initiated by the Golgi tendon organ located in muscle tendons. Like muscle spindles, Golgi tendon organs are also stretch receptors. However unlike the muscle spindle, which acts as a length-detector, the Golgi tendon organ acts as a tension-detector. This difference in sensory function occurs because muscle spindle is disposed in parallel to the extrafusal fibers while the Golgi tendon organ is disposed in series to the extrafusal fibers.
The Golgi tendon organ is innervated by Aα sensory fibers, which are called I-b fibers by sensory physiologists. These afferent fibers terminate on inhibitory interneurons in the dorsal gray horn of the spinal cord. The interneurons terminate on the α- motoneurons in the ventral gray horn of the spinal cord. The Golgi tendon reflex is a protective reflex that prevents excessive rise in muscle tension. When the muscle contracts isometrically, the tendon gets stretched and the tension in the tendon rises markedly. This rise in tension is sensed by the Golgi tendon a which stimulates the I-b afferents. These afferents stimulate the inhibitory interneurons in the spinal cord and thereby, inhibit the α-motoneuron discharge to the muscle, which consequently relaxes. This reflex relaxation of the extrafusal muscle fibers response to rise in muscle tension is called the negative (inverse) stretch reflex.