The brain and the eye – GCSE Combined Science Biology

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The brain and the eye work as a team. The eye collects light from the world, and the brain makes sense of the signals it receives. This lesson looks at both.

It matters because everything you see, feel and remember depends on them. It also explains why glasses help people see clearly, and why brain problems are so hard to treat.

By the end you will be able to name the main parts of the brain and say what each does. You will describe the parts of the eye. You will also explain focusing, the pupil reflex and sight defects.

Regions of the brain

The brain is the coordination centre of the nervous system. Different regions do different jobs, but they work together.

The cerebral cortex is the wrinkled outer layer. It controls consciousness, intelligence, memory and language. Consciousness means being aware of what is happening around you.

The cerebellum sits at the back and controls balance. It also coordinates movement, so your muscles work together smoothly. The medulla controls unconscious activities, which are things you do without thinking, such as breathing and heart rate.

Studying the brain

The brain is very complex, so it is hard to study. Scientists have found out what each region does in three main ways.

They studied patients with brain damage, to see which abilities were lost. They electrically stimulated parts of the brain, to see what response followed. They also use MRI scans, which show which parts of the brain are active during a task.

Treating brain disease and injury is difficult. The brain is delicate and hard to reach, and surgery can cause damage. Many conditions cannot be repaired yet.

Parts of the eye

Light enters the eye through the cornea, the clear front surface. The cornea refracts the light, which means it bends it. The iris is the coloured ring of muscle. It controls how much light gets in through the hole in the middle, called the pupil.

The lens then focuses the light onto the retina. The retina is the layer at the back that has the receptor cells. Rods work in dim light. Cones detect colour.

The optic nerve carries impulses from the retina to the brain, which makes the image.

Focusing on near and far

Accommodation is the way the eye focuses on near and far objects, like a phone camera refocusing. It does this by changing the shape of the lens. Muscles around the lens do this. They are the ciliary muscles, and they pull on the suspensory ligaments, which hold the lens.

To look at something near, the ciliary muscles contract. The ligaments slacken and the lens becomes thicker and more curved. It refracts light more.

To look at something far away, the ciliary muscles relax. The ligaments pull tight and the lens becomes thinner and less curved.

The pupil reflex

The pupil changes size to control how much light reaches the retina. This is a reflex, which is a fast, automatic response.

In bright light, the circular muscles of the iris contract and the radial muscles relax. The pupil gets smaller. This stops too much light damaging the retina.

In dim light, it is the other way round. The radial muscles contract and the circular muscles relax. The pupil gets bigger and more light enters.

Sight defects

In short sight, distant objects look blurred. The light focuses in front of the retina, because the eyeball is too long or the lens is too strong. A concave lens corrects it.

In long sight, near objects look blurred. The light focuses behind the retina, because the eyeball is too short or the lens is too weak. A convex lens corrects it.

Defects can also be treated with contact lenses, with laser surgery to reshape the cornea, or by replacing the lens.

Recap

Cerebral cortex: thought and memory. Cerebellum: balance and coordination. Medulla: breathing and heart rate.

In the eye, the cornea refracts, the iris controls the pupil, the lens focuses and the retina detects light.

Near object: ciliary muscles contract and the lens is thick. Bright light: the pupil gets smaller.

Short sight is corrected with a concave lens. Long sight is corrected with a convex lens.