The brain
- The brain controls complex behaviour. It is made of billions of interconnected neurones and has different regions for different jobs.
- The cerebral cortex is responsible for consciousness, intelligence, memory and language.
- The cerebellum coordinates muscle activity and balance.
- The medulla controls unconscious activities such as heart rate and breathing.
- Scientists study the brain using patients with brain damage, electrical stimulation of different areas and MRI scans. Treating brain damage and disease is difficult because the brain is complex and delicate.
Parts of the eye
- The retina contains receptor cells sensitive to light intensity and colour.
- The optic nerve carries impulses from the retina to the brain.
- The sclera is the tough white outer layer; the cornea is the transparent front part that refracts light into the eye.
- The iris controls the size of the pupil and so how much light enters the eye.
- Ciliary muscles and suspensory ligaments change the shape of the lens to focus light on the retina.
Accommodation
- To focus on a near object, the ciliary muscles contract, the suspensory ligaments loosen, and the lens becomes thicker so it refracts light more.
- To focus on a distant object, the ciliary muscles relax, the suspensory ligaments are pulled tight, and the lens is pulled thin so it refracts light less.
Vision problems
- Myopia (short-sightedness): distant objects look blurred because light is focused in front of the retina. It is corrected with concave lenses.
- Hyperopia (long-sightedness): near objects look blurred because light is focused behind the retina. It is corrected with convex lenses.
- Treatments include glasses, hard and soft contact lenses, laser surgery to change the shape of the cornea, and replacing the lens.
Key terms
- Cerebral cortex
- The part of the brain responsible for consciousness, intelligence, memory and language.
- Cerebellum
- The part of the brain that coordinates muscle activity.
- Medulla
- The part of the brain that controls unconscious activities such as breathing and heart rate.
- Retina
- The layer at the back of the eye containing light-sensitive receptor cells.
- Cornea
- The transparent front of the eye that refracts light.
- Iris
- The coloured ring of muscle that controls the size of the pupil.
- Ciliary muscles
- Muscles that change the shape of the lens.
- Suspensory ligaments
- Fibres that connect the ciliary muscles to the lens.
- Accommodation
- Changing the shape of the lens to focus on near or distant objects.
- Myopia
- Short-sightedness, corrected with a concave lens.
- Hyperopia
- Long-sightedness, corrected with a convex lens.