reciprocal innervation

Reciprocal innervation is a fundamental principle in physiology that describes how muscles with opposite functions work together. When one muscle or group of muscles contracts, the opposing muscles relax. This coordinated action ensures smooth and efficient movement.

For example, when you flex your arm, the biceps muscle contracts, while the triceps muscle on the back of your arm relaxes. This is achieved through nerve signals sent from the spinal cord. Afferent nerve fibers from the contracting muscle stimulate inhibitory interneurons, which then inhibit the motor neurons controlling the antagonist muscle, causing it to relax. This principle is crucial for most body movements, including walking and eye movements.1