The eyes have it.When night falls, it's difficult to see well. To see better, you turn on a light. When the sun rises, you turn the light off because you don't need it any longer. What you really are trying to do is control the amount of light around you. Your eyes can control the amount of light, too. Let's take a closer look. In the center of your eye is a colored ring called the iris. Light enters your eye through the pupil, a round, black opening in the center of your iris. Two muscles in the iris control the amount of light entering the pupil. The sphincter muscle Noun 1. sphincter muscle - a ring of muscle that contracts to close an opening anatomical sphincter, sphincter muscle, musculus - one of the contractile organs of the body forms a circle around the pupil. The dilator dilator /di·la·tor/ (di-lat´er) 1. a structure that dilates, or an instrument used to dilate. 2. dilator muscle. di·la·tor n. 1. muscle moves away from the pupil like bicycle bicycle, light, two-wheeled vehicle driven by pedals. The name velocipede is often given to early forms of the bicycle and to its predecessor, the dandy horse, a two-wheeled vehicle moved by the thrust of the rider's feet upon the ground. spokes. These eye muscle patterns are different for everyone. In fact, they are as individual as your fingerprints Impressions or reproductions of the distinctive pattern of lines and grooves on the skin of human fingertips. Fingerprints are reproduced by pressing a person's fingertips into ink and then onto a piece of paper. . Look closely at your iris in a mirror. Can you see the sphincter sphincter /sphinc·ter/ (sfingk´ter) [L.] a ringlike muscle which closes a natural orifice or passage.sphinc´teralsphincter´ic anal sphincter , sphincter a´ni and dilator muscles? The muscles of the iris have two important, but completely different jobs. Together they work like window blinds to control the amount of light entering your eye. Here's how: If there's too much light entering your eye--the sphincter muscle tightens around the pupil, making it smaller so less light can enter. If there's not enough light entering your eye--the dilator muscle pulls the pupil open wider, letting in more light. Your brain controls these movements. It senses the amount of light inside your eye. It then lets the iris know whether to enlarge TO ENLARGE. To extend; as, to enlarge a rule to plead, is to extend the time during which a defendant may plead. To enlarge, means also to set at liberty; as, the prisoner was enlarged on giving bail. or decrease the size of your pupil. Your eyes and brain work together as built-in window shades! |
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