2.87 Response: Eyes

understand the function of the eye in focusing near and distant objects, and in responding to changes in light intensity

Light --[Cornea --> Lens --> Focused on retina]--> Eye

1. Retina
- Rods and cones; cells sensitive to light
        - Rods: Dim light
        - Cones: Colour and details
- Responds to stimuli (light) by sending impulses to the brain along optic nerve
- Image on retina is inverted
- Brain flips image right way up

2. Focusing
- Cornea bends most of the light rays
- Lens can also bend rays slightly
- Shape of lens controlled by ciliary muscles

Source: http://www.sapdesignguild.org/editions/edition9/images/accomodation.png

3. Focusing on a distant object
- Ciliary muscles relax
- Suspensory ligaments tighten
- Lens pulled into thin shape
- Distant object focused onto retina

4. Focusing on a near object
- Ciliary muscles contract
- Suspensory ligaments relax
- Lens thickens
- Near object focused onto retina

5. Response to changes in light intensity
- Iris: controls amount of light allowed to enter the eye
- Contains circular and radial muscles

a) Bright light
- Circular muscles contract, radial muscles relax
- Pupil is made smaller/constricts
- Too much light entering the eyes can cause damage

b) Dim light
- Circular muscles relax, radial muscles contract
- Pupil is made bigger/dilates
- Aids seeing in darker places

Source: http://michellebiology.blogspot.com