A proprioceptive receptor found embedded in muscle tendons consisting of encapsulated bundles (or fibrils) of collagen, which attach some 3 to 50 muscle fibers to tendons (see figure below). Innervated by a single, large, rapidly conducting afferent fiber (afferent Ib fiber so labeled to distinguish it from the Ia primary afferent that supplies the muscle spindle), it is compressed and activated by any increase of the tendon’s tension, due either to active contraction or passive stretch of the corresponding muscle. If activation is strong enough, it produces an action potential. After entering the spinal cord, the sensory axon of the organ synapses on inhibitory interneurons that in turn synapse on motoneurons. Such inhibition provides a smoothing signal as muscle contraction progresses. Another discovery accredited to Camillo Golgi (1844-1926) who gave the first comprehensive description in 1880.
Golgi tendon organ showing its afferent Ib fiber, its fixation in a tendon and its attachment to muscle fibers, as well as collagen fibrils that make it up.
See Action potential, Axon, Collagen, Interneurons, Monosynaptic and polysynaptic reflex, Motoneuron, Muscle fiber, Muscle spindle, Proprioception, Reflex