Iris radial muscles are responsible for which action?

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Multiple Choice

Iris radial muscles are responsible for which action?

Iris radial muscles are the dilator part of the iris. When they contract, they pull the iris outward like spokes on a wheel, enlarging the pupil to let more light in. This dilation happens in dim light or during situations that require more light or heightened alertness, driven by the sympathetic system. The muscle that actually narrows the pupil is a circular band called the sphincter pupillae, so closing the pupil isn’t due to the radial fibers. The iris doesn’t rotate, and changing the cornea’s shape isn’t controlled by the iris at all—shape changes in near vision involve the lens and ciliary muscle, not the iris. So the action produced by the iris radial muscles is opening the pupil.

Iris radial muscles are the dilator part of the iris. When they contract, they pull the iris outward like spokes on a wheel, enlarging the pupil to let more light in. This dilation happens in dim light or during situations that require more light or heightened alertness, driven by the sympathetic system. The muscle that actually narrows the pupil is a circular band called the sphincter pupillae, so closing the pupil isn’t due to the radial fibers. The iris doesn’t rotate, and changing the cornea’s shape isn’t controlled by the iris at all—shape changes in near vision involve the lens and ciliary muscle, not the iris. So the action produced by the iris radial muscles is opening the pupil.

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