Cambridge O Level Biology · Syllabus 5090 · Coordination and Control
Retina
What is Retina?
The light-sensitive layer lining the inside of the back of the eye. It contains light receptor cells, some of which are sensitive to different colours. Light focused onto the retina generates electrical impulses that travel along the optic nerve to the brain.
This definition is part of the Coordination and Control chapter in Cambridge O Level Biology.
Common mistakes with Retina
- Write it carefully. "The eye sees the object" will not earn a mark on a question about receptors. "Light receptors in the retina detect the light and impulses are sent along the optic nerve to the brain, where they are interpreted" earns several.
Questions students ask about Retina
What are the parts of the eye and what do they do?
The cornea refracts light entering the eye. The iris contains muscles that control the size of the pupil, which is the opening light passes through. The lens refracts light and focuses it on the retina, changing shape to do so. The ciliary muscles alter the tension in the suspensory ligaments, which are attached to the lens. The retina contains the light receptor cells, and the fovea is the region of the retina with the greatest density of them. The optic nerve carries impulses to the brain, and the blind spot is the point where it leaves, containing no light receptors.
What happens to the pupil in bright light?
The circular muscles of the iris contract and the radial muscles relax, so the pupil becomes smaller. Less light then reaches the retina, which reduces the risk of damage to the light receptors. In dim light the reverse happens: the radial muscles contract, the circular muscles relax, and the pupil becomes larger.
What is accommodation?
Accommodation is the change in shape of the lens that focuses a sharp image of a near or distant object on the retina. For a near object the ciliary muscles contract, the suspensory ligaments slacken, and the lens becomes thicker and more convex, refracting light more. For a distant object the ciliary muscles relax, the suspensory ligaments tighten, and the lens becomes thinner and less convex, refracting light less. Accommodation does not change the size of the pupil.