The Brain and the Eye

The brain is the most complex organ in the body, and the eye is the sense organ that supplies it with most of our information about the world. This lesson looks at both. It covers the main regions of the brain and what they do, how neuroscientists manage to study an organ so delicate, and why brain damage and tumours are so hard to treat. It then turns to the eye: its structure, how it focuses light on near and distant objects (accommodation), the pupil reflex, and the common vision defects of short and long sight and how lenses correct them. This is part of Topic B3 of OCR Gateway Science A.

Separate science / Higher note: Much of the detail in this lesson — particularly the named regions of the brain, the methods used to study the brain, and the detail of vision defects and accommodation — is content for the separate (triple) Biology course and for Higher tier candidates. Where a section is clearly beyond the Foundation core, it is flagged. Always check which tier and which course you are sitting.

By the end of this lesson you should be able to name the main parts of the brain and their functions, describe how the brain is studied, label the parts of the eye and explain their roles, describe accommodation and the pupil reflex, and explain how short and long sight are corrected.

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The Brain

The brain is part of the central nervous system. It is made of billions of interconnected neurones and it controls everything from heartbeat and breathing to memory, language and conscious thought. It is protected by the bones of the skull and is connected to the rest of the body through the spinal cord.

Main regions of the brain (separate science / Higher)

You should be able to name three main regions and give a function for each.

#	Region	Main function
1	Cerebrum (cerebral cortex)	The large, folded outer region; controls conscious thought, memory, language, intelligence and voluntary movement
2	Cerebellum	At the back, below the cerebrum; controls balance, posture and coordination of muscular movement
3	Medulla (medulla oblongata)	At the base, joining the spinal cord; controls unconscious activities such as heart rate and breathing rate

A simple way to remember them: the cerebrum is for thinking, the cerebellum is for coordinating movement and balance, and the medulla keeps you alive by running the automatic functions you never think about.

How neuroscientists study the brain (separate science / Higher)

The brain is extremely complex and very delicate, and it is encased in the skull, so studying it is difficult. Neuroscientists have used three main approaches:

• Studying patients with brain damage. If a small area is damaged (by injury, a stroke or surgery) and a particular ability is lost, that area is likely to be involved in that ability. This is how many functions were first mapped.
• Electrically stimulating the brain. A tiny electrical current applied to a specific region can produce a response (such as a movement or a sensation), showing what that region does.
• Scanning with MRI (magnetic resonance imaging). An MRI scanner produces detailed images of the brain's structure, and certain scans can show which areas become active during particular tasks (such as speaking or remembering). Scans allow the brain to be studied without surgery.

Exam Tip: If asked how the brain is studied, give the three methods — damaged patients, electrical stimulation and MRI scanning — and note that scanning is valuable because it is non-invasive (it does not require opening the skull).

Why brain damage and tumours are hard to treat (separate science / Higher)

Treating problems inside the brain and spinal cord is notoriously difficult for several reasons:

• The brain is delicate and easily damaged, and it is encased in the skull, making it hard to reach with surgery.
• The brain is extremely complex and not yet fully understood, so it is hard to know exactly which region is responsible for a problem.
• Nervous tissue in the brain and spinal cord does not readily repair itself once damaged.
• Many drugs cannot reach the brain because they are blocked from passing out of the blood into brain tissue, so treating tumours and infections with medicines is harder.
• Operating risks damaging healthy tissue nearby, which could cause permanent loss of function.

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The Eye

The eye is a sense organ that contains light receptors. It detects light (the stimulus), focuses it to form an image, and converts it into electrical impulses that travel to the brain along the optic nerve.

Structure of the eye

#	Part	Function
1	Cornea	Transparent front of the eye; refracts (bends) light, doing most of the focusing
2	Iris	Coloured ring of muscle; controls the size of the pupil
3	Pupil	The hole in the middle of the iris that lets light in
4	Lens	Focuses light onto the retina; can change shape to fine-tune focus
5	Ciliary muscles	Ring of muscle that changes the shape of the lens
6	Suspensory ligaments	Connect the ciliary muscles to the lens
7	Retina	Light-sensitive layer at the back containing light receptors
8	Optic nerve	Carries electrical impulses from the retina to the brain