Main parts of the brain
- Cerebrum: the largest part, with a wrinkled outer layer (cortex). It has a left and right half (hemispheres) joined by a bridge of fibres. It handles thinking, senses, language and voluntary movement. The left half controls the right side of the body and the other way round.
- Cerebellum: at the back, below the cerebrum. It keeps balance and makes movements smooth and accurate.
- Brainstem: joins the brain to the spinal cord. It runs automatic jobs: breathing, heartbeat, swallowing, sleep and waking.
The brain is about 2% of body mass but uses about 20% of the body’s energy.
Neurons and synapses
A neuron has a cell body, short branches called dendrites that receive messages, and a long axon that sends them. A message travels along the axon as an electrical impulse. At the end there is a tiny gap, the synapse. There the neuron releases chemicals (neurotransmitters) that reach the next neuron. Learning changes how strong these connections are; this is called neuroplasticity.
The brain map: lobes, speech centres and mirror neurons
- Frontal lobe: planning, decisions, self-control, voluntary movement (motor cortex).
- Parietal lobe: touch, pain, temperature and the sense of where things are.
- Temporal lobe: hearing, understanding language, parts of memory.
- Occipital lobe: vision.
Speech centres
Broca’s area (frontal lobe, usually left side) helps produce speech. Damage makes speech slow and broken, though understanding is fine. Wernicke’s area (temporal lobe) helps understand language. Damage gives fluent speech that makes little sense.
Mirror neurons
Some neurons in motor areas fire both when we do an action and when we watch someone else do it. Scientists think they help in copying, learning skills and understanding others, though their exact role is still studied.
Memory and emotions
- Hippocampus: turns new experiences into long-term memories. Sleep helps this.
- Amygdala: detects danger and adds emotion such as fear. Emotional events are remembered more strongly.
- Prefrontal cortex (front of the frontal lobe): calms strong emotions and helps working memory.
Memory types: short-term (seconds, a few items) and long-term (facts, events, skills). Repetition, sleep and spaced revision make memories last.
Brain and body: movement, breathing and circulation
The brain sends signals through nerves to skeletal muscles. Muscles pull on bones across joints like levers. Regular exercise makes muscle fibres thicker and stronger, and practice makes the brain’s control smoother.
The brainstem sets the rate of breathing and heartbeat by sensing carbon dioxide in the blood. Doctors measure these with:
- EEG (electroencephalogram): brain waves from electrodes on the scalp. Fast small waves when alert, slow large waves in deep sleep.
- ECG (electrocardiogram): the electrical signal of each heartbeat (P wave, QRS complex, T wave).
- Spirogram: a graph of air breathed in and out, showing tidal volume and vital capacity.
Try it: a reaction-time test
A friend holds a 30 cm ruler above your open fingers and drops it without warning. Catch it and note the cm mark. Shorter distance = faster reaction. Repeat 5 times: does practice help? Your eyes (occipital), decision (frontal) and hand muscles (via the motor cortex and cerebellum) all take part.
Key formulas and definitions
- Cerebrum = thinking, senses, voluntary movement
- Cerebellum = balance and coordination
- Brainstem = breathing, heartbeat, sleep
- Neuron: dendrite → cell body → axon → synapse
- Lobes: Frontal, Parietal, Temporal, Occipital
- Broca = speaking; Wernicke = understanding
- Hippocampus = memory; amygdala = emotion
- EEG = brain, ECG = heart, spirogram = lungs
Worked examples
1. A person can understand questions but speaks in short, broken words. Which area is likely damaged?
Broca’s area in the frontal lobe, which builds speech. Understanding (Wernicke’s area) is fine.
2. After a hit to the back of the head, a player has blurred vision. Which lobe is involved?
The occipital lobe at the back of the brain handles vision.
3. A signal travels along a 1 m long nerve at 100 m/s. How long does it take?
time = distance ÷ speed = 1 ÷ 100 = 0.01 s = 10 ms.
4. In a ruler-drop test the ruler falls 20 cm. Find the reaction time (g = 10 m/s²).
d = ½gt², so t = √(2d/g) = √(2 × 0.20 / 10) = √0.04 = 0.2 s.
5. Why do we remember our first day at a new school better than an ordinary Tuesday?
Strong emotions activate the amygdala, which boosts the hippocampus in storing the memory.
Common mistakes
- Mixing up cerebrum and cerebellum: the cerebellum is the small part at the back for balance.
- Thinking the left brain controls the left hand: control is crossed.
- Swapping Broca (speaking) and Wernicke (understanding).
- Believing we use only 10% of the brain: scans show all areas are active at different times.