Summary
Highlights
Golgi Tendon Organs (GTOs) are proprioceptive organs found in muscle tendons. This video will cover their basic anatomy, function, and the associated reflex arc.
Skeletal muscles attach to bones via tendons, composed of dense regular connective tissue with collagen fibers. When muscles contract and shorten, they pull on tendons, stretching these collagen fibers. GTOs are clusters of sensory receptors that detect this stretch, measuring the degree of tension generated by the muscle. The more force a muscle generates, the greater the stretch on these fibers, leading to a higher rate of action potentials sent by the GTOs to the brain, allowing it to monitor muscle tension.
Beyond proprioception, GTOs have a crucial protective function. If a muscle generates too much force, the GTOs trigger a reflex that causes the contracted muscle to relax and its antagonist muscle to contract. This prevents damage to the tendon, such as tearing it from the bone. Examples with bicep curls demonstrate how GTO firing increases with greater weight, and how at extreme weights, the GTOs would inhibit the bicep to prevent injury.
When excessive force is detected, GTOs send signals to the spinal cord via afferent neurons (type 1b). These neurons synapse with interneurons. One interneuron inhibits the motor neuron of the contracting muscle (e.g., quadriceps), causing it to relax and reduce force. Another interneuron activates the motor neuron of the antagonist muscle (e.g., hamstrings), causing it to contract. This polysynaptic reflex protects the muscle and tendon from damage by reducing the force of the primary muscle and engaging the opposing muscle.
GTOs serve two main functions: monitoring muscle tension for proprioception and initiating a protective polysynaptic reflex to prevent injury when excessive force is generated, causing the primary muscle to relax and the antagonist to contract.