The functions of the main regions of the brain (cerebral cortex, cerebellum, medulla), the structure of the eye and how it focuses light, accommodation, and how the eye responds to changes in light intensity (Higher tier content).

What this dot point is asking

This is Higher tier content. OCR wants you to state the functions of the main regions of the brain, describe the structure of the eye, explain how the eye focuses light (accommodation), and explain how the eye responds to changes in light intensity.

The regions of the brain

The brain is the part of the CNS that coordinates conscious and unconscious activities. You need three regions:

• Cerebral cortex. The outer, folded layer. It controls conscious thought, memory, intelligence, language and voluntary (conscious) movement.
• Cerebellum. At the back of the brain. It coordinates movement and balance, making movements smooth and precise.
• Medulla (medulla oblongata). At the base of the brain. It controls unconscious activities such as heart rate and breathing.

The brain is difficult to study because it is very complex, delicate and protected inside the skull, so accessing it risks damage. Scientists learn about it by studying people with brain damage, by stimulating regions electrically, and by using scans such as MRI.

The structure of the eye

The eye is the receptor organ for light. Its main parts are:

• Cornea. The transparent front layer that refracts (bends) light as it enters.
• Iris. The coloured ring of muscle that controls the size of the pupil, and so how much light enters.
• Pupil. The hole in the middle of the iris that light passes through.
• Lens. Focuses the light onto the retina; it can change shape (accommodation).
• Ciliary muscles and suspensory ligaments. Control the shape of the lens.
• Retina. The light-sensitive layer at the back, containing receptor cells that detect light and send impulses to the brain.
• Optic nerve. Carries impulses from the retina to the brain.

Accommodation: focusing the lens

To focus on a near object:

• The ciliary muscles contract.
• The suspensory ligaments slacken (loosen).
• The lens becomes thicker and more curved, so it refracts the light more strongly.

To focus on a distant object:

• The ciliary muscles relax.
• The suspensory ligaments pull tight.
• The lens becomes thinner and less curved, so it refracts the light less.

Responding to light intensity (the iris reflex)

The iris reflex controls the amount of light entering the eye, protecting the retina from damage:

• In bright light, the circular muscles of the iris contract and the radial muscles relax, making the pupil smaller, so less light enters.
• In dim light, the radial muscles contract and the circular muscles relax, making the pupil larger, so more light enters.

This is a reflex, so it happens automatically without conscious thought.