Eye

1. Sense organs are groups of receptor cells that respond to a specific stimulus (light).

1.1. Other sense organs respond to temperature, touch, sound and chemicals.

2. Cornea

2.1. Transparent layer which coats the iris and refracts light into the eye.

3. Iris

3.1. Coloured section that controls how much light enters the pupil by contracting/dilating.

4. Pupil

4.1. "Hole" in the iris allows light to pass through to the lens.

5. Retina

5.1. Contains light receptors (rod/cone cells) sensitive to lights of different colours.

6. Fovea

6.1. Light is focused here when you look directly at an object and has the greatest number of receptors (cone cells).

7. Optic Nerve

7.1. Carries nerve impulses to the brain.

8. Pupil reflex

8.1. Bright light may damage the retina. Muscles in the iris contract, making the diameter of the pupil smaller to ensure less light enters (reflex action).

9. Photoreceptor cells

9.1. Rods

9.1.1. Sensitive to dim light. Used for night vision.

9.1.1.1. Located around the periphery of the retina.

9.2. Cones

9.2.1. Sensitive to bright light. See colour such as red, green and blue light.

9.2.1.1. Concentrated at the fovea.

10. Accomodation

10.1. Changes that occur in the eye to focus on objects at different distances.

10.2. Close object

10.2.1. Lens need to be wide and thick to refract light more strongly. Suspensory ligaments must be loose to hold the lens in position. Ciliary muscles to which the ligaments are attached need to contract.

10.3. Far object

10.3.1. Lens need to be narrow and thin to refract light less strongly. Suspensory ligaments must be pulled tight and ciliary muscles relax.