Iris sphincter muscle Iris sphincter muscle The iris sphincter muscle (pupillary sphincter, pupillary constrictor, circular muscle of iris, circular fibers) is a muscle in the part of the eye called the iris. It encircles the pupil of the iris, appropriate to its function as a constrictor of the pupil. It is found in vertebrates and some cephalopods. Initially, all the myocytes are of the smooth muscle type but, later in life, most cells are of the striated muscle type. Its dimensions are about 0.75 mm wide by 0.15 mm thick. In humans, it functions to constrict the pupil in bright light (pupillary light
Muscle coactivation ground. It is also believed to be important for postural control by stabilizing the spine. Muscle coactivation is absolutely necessary for learning a fine motor skill or for any activity involving stability. In order for muscle coactivation to occur, it must inhibit reciprocal innervation, which occurs when a muscle contracts and the synergist muscle relaxes. For muscle coactivation to occur, both the muscle and synergist muscle need to contract. Muscle coactivation is measured using a technique called electromyography(EMG). This is performed by using surface EMG that responds to electrical activity of the muscle through the skin. Electrical activity is only