Chapter: 3 Movement in & out of Cells

To allow it to adjust the size of the pupil , the iris contains muscles.

• To allow it to adjust the size of the pupil , the iris contains muscles.
• Circular muscles are arranged in circles around the pupil .
• When they contract, they make the pupil get smaller.
• Radial muscles run outwards from the edge of the pupil dilate, or get larger.
• This is called the iris reflex or the pupil reflex .
• The circular muscles and radial muscles are antagonistic muscles.
• They work together to control an action and have opposite effects.
• When one muscle contract, the other relaxes.