The sphincter pupillae muscle is controlled by the parasympathetic fibers of the oculomotor nerve (cranial nerve III). Activation of these fibers causes constriction of the pupil (miosis).
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The external anal sphincter is primarily supplied by the inferior rectal nerve, a branch of the pudendal nerve.
Sphincter muscles are circular muscles that control the opening and closing of various body passages and openings. They help regulate the flow of substances, such as food or waste, through these passages by contracting and relaxing. Examples include the sphincter muscles of the gastrointestinal tract and the urinary system.
A sphincter muscle controls a circular opening in the body. It serves to regulate the passage of substances through the opening by contracting or relaxing. Examples include the anal sphincter and the sphincter muscles in the digestive system.
The cranial nerve that innervates the ear is the vestibulocochlear nerve (CN VIII). It has two branches: the vestibular nerve that controls balance and the cochlear nerve that controls hearing.
An abducent nerve is a nerve which controls the lateral rectus muscle in the eye.