antagonist (muscle)

A muscle that has the opposite primary action to another muscle in the same eye. For example, the lateral rectus abducts the eye while its antagonist, the medial rectus, adducts the eye. Antagonist muscles work in pairs to produce smooth, coordinated eye movements. When one muscle contracts, its antagonist relaxes, allowing the eye to move in the desired direction. This reciprocal innervation is essential for precise ocular motility.