The iris in the human eye contracts and expands, controlling the amount of light that reaches the retina. What types of muscle control this?To which skeletal system does the sternum belong?

1. sphincter muscle and dilator muscle

2. Axial skeleton

Explanation:

1.The iris in the human eye is responsible for controlling the exposure of of light that reaches the retina. The movement of iris is controlled by a muscles called sphincter muscle and dilator muscle. sphincter muscle constricts the pupil in bright light while dilator muscle expands the pupil.

2.  Sternum belongs to the axial skeleton, which is a long flat bone located in the central part of the chest. Axial skeleton consists of 80 bones and strenum is one of them. Axial skeleton functions to provide protection to vital organs such as brain, heart and lungs. Strenum functions to protect heart.

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