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.

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).

2The Hypothalamus — the internal "thermostat and messenger"

The hypothalamus sits just above the pituitary gland and constantly monitors the blood as it passes through the brain. When it detects that something is off-balance, it either releases hormones directly or tells the pituitary gland to release hormones — making it central to several homeostatic mechanisms (the body's self-regulating processes).

Its four key jobs to know:

• Regulating body temperature — monitors blood temperature and triggers a response if it strays too high or low.
• Osmoregulation — monitors the water balance (concentration) of the blood. If blood is too concentrated, it releases ADH, which increases water reabsorption in the kidneys.
• Regulating digestive activity — controls hormones linked to appetite and digestive enzyme secretion.
• Controlling endocrine functions — triggers the pituitary gland to release hormones controlling metabolism, growth, puberty, sexual function, sleep, and mood.

3Pituitary Gland — the "master gland"

Sitting directly below the hypothalamus, the pituitary gland produces a wide range of hormones. Some act directly on the body; others act as a trigger, stimulating other endocrine glands to release their own hormones — which is why it's nicknamed the "master gland."

It has two functionally distinct sections:

• Anterior pituitary — produces and releases its own hormones.
• Posterior pituitary — doesn't make its own hormones; it stores and releases hormones that were actually made by the hypothalamus, e.g. ADH and oxytocin.

4The Cerebellum — movement's fine-tuner

The cerebellum's job is to coordinate movement. This includes balance — which sounds simple but is actually a highly complex task, requiring constant coordination between the eyes, the semicircular canals in the ears (which detect head movement), and dozens of muscles working together in real time.

5The Medulla Oblongata — the survival core

Also just called the medulla, this region controls unconscious, involuntary functions — the stuff that keeps you alive without you ever thinking about it. Two coordination centres to know:

• Cardiac centre → controls heart rate
• Respiratory centre → controls breathing rate

Critically, the medulla controls functions essential to staying alive, even if other parts of the brain are damaged. This is why, medically, damage to the medulla is far more immediately life-threatening than damage to, say, the cerebrum.

1CT (Computerised Tomography)

CT scans use x-ray radiation. A beam of x-rays is fired at the patient from all angles, and digital detectors pick up the x-rays as they exit the body on the other side. The key physical principle: denser tissue absorbs more x-ray radiation, so it shows up as a lighter region on the resulting image.

• Shows physical structure only — good for spotting tissue damage.
• Example: blood is less dense than brain tissue, so a CT scan can reveal bleeding/damaged blood vessels after a stroke.
• Doesn't directly show function — but doctors can infer function by linking a patient's visible symptoms to the location of scan-detected damage.
• Not recommended for pregnant patients or children due to higher x-ray exposure than a standard x-ray (though the actual risk of harm remains very low).

2MRI (Magnetic Resonance Imaging)

MRI uses a combination of a magnetic field and radio waves — no x-rays at all. The patient lies inside a large magnet and must stay very still.

• Produces higher resolution images than CT and shows soft tissue clearly.
• Like CT, it only shows structure — function can only be inferred by linking visible damage to symptoms.
• Especially good for tumour diagnosis, since tumours show up clearly.
• More expensive than CT, but avoids the risk of x-ray radiation — often preferred for long-term therapy monitoring.
• Cannot be used on patients with pacemakers or insulin pumps — the magnetic field can interfere with these devices.

3fMRI (Functional MRI)

fMRI works like normal MRI (same magnetic field + radio waves) but with one crucial upgrade: it can show brain function in real time.

How? It measures the ratio of oxygenated to deoxygenated haemoglobin in the blood. Active brain regions demand more oxygen, so more oxygenated blood flows there — and that region "lights up" on the scan. A patient can be asked to perform a task, answer a question, or think about a topic while inside the scanner, and researchers can watch which regions respond.

Used in medical diagnosis (e.g. finding the source of seizures) and in psychology research.

4PET (Positron Emission Tomography)

PET scans use radioactive tracers introduced into the blood before the scan. These tracers collect in areas with increased blood flow, metabolism, or neurotransmitter activity. A classic example is radioactively labelled glucose — since glucose is transported in the blood and used heavily by metabolically active cells, it builds up in the most active brain regions.

• The scanner detects areas of high radioactivity, tracking tracer movement and accumulation.
• The amount of tracer in a region indicates whether that region is active or inactive.
• Useful for studying diseases like Alzheimer's, where activity decreases in certain regions — PET can visualise that decline.

1Parkinson's Disease

Parkinson's disease is a brain disorder that affects the co-ordination of movement. It's caused by the progressive loss of neurones in specific parts of the brain — specifically, the neurones that normally produce the neurotransmitter dopamine, which plays a key role in muscle control.

Symptoms: tremors in specific body parts, slow movement, stiff/inflexible muscles, difficulties with balance, and changes to speech.

Treatments target different points in this chain:

• Dopamine agonists — mimic dopamine by directly binding to and activating dopamine receptors on the postsynaptic membrane.
• Dopamine precursors (e.g. L-dopa) — chemicals that get converted into dopamine once inside the neurones, effectively topping up dopamine production.
• Enzyme inhibitors — e.g. Monoamine Oxidase B (MAOB) inhibitors block the enzymes that would normally break down dopamine in the synaptic cleft, so dopamine levels stay higher for longer.

Future research directions include gene therapy (adding genes to boost dopamine production or protect dopamine-producing cells from destruction) and stem cell therapy (replacing lost dopamine-producing cells entirely).

2Depression

Low levels of the neurotransmitter serotonin have been linked to depression. Serotonin transmits nerve impulses through the areas of the brain that control mood, so when serotonin levels drop, episodes of depression become more likely. Noradrenaline and dopamine have also been linked to depression.

Antidepressant drugs work by increasing the levels of relevant neurotransmitters in the brain, using several different mechanisms:

• SSRIs (Selective Serotonin Reuptake Inhibitors) — prevent the reuptake of serotonin at synapses, meaning it isn't reabsorbed as quickly and stays active in the synaptic cleft for longer, raising overall serotonin levels.
• TCAs (Tricyclic Antidepressants) — increase levels of both serotonin and noradrenaline in the brain.
• MAOB inhibitors — same principle as in Parkinson's treatment: they block the enzymes that would otherwise break down neurotransmitters in the synaptic clefts, so more neurotransmitter remains available.