The Brain

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Edexcel IAL Biology · Nervous System

The Brain

Big idea: Different regions of the brain are physically specialised for different jobs — some run things you never think about (like breathing), others handle conscious thought — and scientists can now watch these regions light up in real time using scanners like fMRI and PET, which is how we know which bit does what.

Summary — What This Chapter Covers

The brain + spinal cord = the central nervous system (CNS), built from billions of interconnected neurones.
The brain isn't one lump — it has distinct regions (cerebrum, hypothalamus, pituitary gland, cerebellum, medulla oblongata), each doing a different job.
The cerebrum handles conscious activity (thought, vision, speech, memory) and is split into two hemispheres joined by the corpus callosum.
The medulla oblongata runs unconscious survival functions like heart rate and breathing.
Four main scanning techniques let scientists study the living brain without surgery: CT, MRI, fMRI, PET — each with a different trade-off between structure, function, cost, and safety.
Neurotransmitter imbalances cause real diseases: low dopamine → Parkinson's disease; low serotonin → linked to depression. Drugs treat these by manipulating neurotransmitter levels at the synapse.

Topic 1: Human Brain Structures & Functions

1The Cerebrum — the "conscious control centre"

The cerebrum is the biggest part of the human brain — about 80% of total brain mass. Basically, whenever you're doing something you're aware of doing — seeing, hearing, talking, thinking, remembering — the cerebrum is behind it.

Think of it like this: if your brain were a company, the cerebrum is the head office where all the deliberate decision-making happens — reading this sentence, deciding what to have for lunch, recalling your friend's birthday. Everything "on purpose" runs through here.

The cerebrum is split into two cerebral hemispheres, connected by a thick band of nerve fibres called the corpus callosum (literally the "bridge" that lets the two halves talk to each other). Confusingly for your intuition, the wiring is crossed:

Right hemisphere → controls the left side of the body
Left hemisphere → controls the right side of the body

Zoom into the cerebrum's structure and you find two layers:

Cerebral cortex (grey matter) — the thin outer layer made of neurone cell bodies. It's heavily folded (all those wrinkles you see in brain pictures), and that folding is not decoration — it dramatically increases surface area, which means more neurones can be packed in, which means more possible connections, which means the brain can support more complex behaviour.
White matter — underneath the cortex, made of myelinated axons that carry signals between neurones (myelin is what makes it look pale/white compared to the darker cell-body-rich grey matter).

Logic Chain to Remember More folding → more surface area → more neurones fit → more connections → more complex behaviour possible.

This single chain of reasoning explains why cortex folding is evolutionarily significant, and it's a favourite thing for exam questions to test.

Practice Question

Explain why the highly folded structure of the cerebral cortex is important for brain function.

2The Hypothalamus — the internal "thermostat and messenger"

monitors the blood

3

4

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3Pituitary Gland — the "master gland"
4The Cerebellum — movement's fine-tuner
5The Medulla Oblongata — the survival core
1CT (Computerised Tomography)
2MRI (Magnetic Resonance Imaging)
3fMRI (Functional MRI)
4PET (Positron Emission Tomography)
1Parkinson's Disease

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