Overview
This lecture covers the pupillary mechanism of the eye, explaining how the pupil changes size in response to light and the roles of specific muscles in this process.
Structure of the Eye Related to the Pupillary Mechanism
- The iris is the colored part of the eye, made of muscle tissue.
- The iris includes two muscle types: outer radial muscles (radiate outward) and inner circular muscles (form a ring around the pupil).
- The pupil is the central black opening that lets light enter the eye.
Purpose and Function of the Pupillary Mechanism
- The pupillary mechanism controls the size of the pupil to regulate the amount of light entering the eye.
- Adjusting pupil size protects the eye from too much or too little light, aiding vision in different lighting conditions.
Pupil Response in Different Light Conditions
In Dim Light
- Radial muscles contract.
- Circular muscles relax.
- The pupil dilates (gets bigger).
- More light enters the eye.
In Bright Light
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Radial muscles relax.
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Circular muscles contract.
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The pupil constricts (gets smaller).
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Less light enters the eye.
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The process for dim and bright light is opposite; learning one helps recall the other.
The Pupillary Mechanism as a Reflex
- The pupillary mechanism is an example of a reflex action.
- Exam questions may ask to explain both the pupillary mechanism and the reflex arc involved.
Key Terms & Definitions
- Pupil — Black central opening allowing light to enter the eye.
- Iris — Colored part of the eye, made of muscle, that changes pupil size.
- Radial Muscles — Outer iris muscles that contract to enlarge the pupil.
- Circular Muscles — Inner iris muscles that contract to shrink the pupil.
- Pupillary Mechanism — Process controlling pupil size in response to light.
Action Items / Next Steps
- Review the roles of radial and circular muscles in pupil adjustment.
- Practice explaining the pupillary mechanism as a reflex for exam preparation.
- Know key terms and be able to apply them to diagram-based questions.