Question
Describe the three major parts of the brain — cerebrum, cerebellum, and medulla oblongata — and explain their functions. What happens when each is damaged?
Solution — Step by Step
The human brain has three main regions:
- Forebrain — cerebrum, thalamus, hypothalamus
- Midbrain — relay centre between forebrain and hindbrain
- Hindbrain — cerebellum, pons, medulla oblongata
Each region evolved to handle a different level of processing — from complex conscious thought (cerebrum) to rapid movement coordination (cerebellum) to basic survival functions (medulla).
The brain is protected by the skull and three membranes called meninges, and cushioned by cerebrospinal fluid (CSF).
The cerebrum is the largest brain structure (~80% of brain mass) and is divided into left and right hemispheres connected by the corpus callosum.
Its outer layer — the cerebral cortex — is highly folded (folds = gyri, grooves = sulci) to pack more neurons into less space. More surface area = greater processing capacity.
Functional areas of the cerebral cortex:
| Lobe | Location | Key Functions |
|---|---|---|
| Frontal | Front | Voluntary movement, reasoning, planning, Broca’s area (speech) |
| Parietal | Top-middle | Sensations of touch, pressure, pain, temperature |
| Temporal | Sides | Hearing, memory, Wernicke’s area (language comprehension) |
| Occipital | Back | Vision and visual interpretation |
Damage to cerebrum: Effects depend on which area — Broca’s area damage causes expressive aphasia (can’t speak, but can understand); occipital damage causes blindness even with intact eyes.
The cerebellum (“little brain”) sits at the back-bottom of the skull and also has two hemispheres and a folded cortex. It does NOT initiate movement — that is the cerebrum’s job.
What the cerebellum does:
- Coordinates voluntary muscles for smooth, precise movement
- Maintains posture and balance (using input from inner ear vestibular system)
- Coordinates eye movements
- Involved in motor learning — learning to ride a cycle, play piano
Damage to cerebellum → Ataxia: Movements become jerky and uncoordinated. Walking becomes unsteady (like being intoxicated). Fine motor tasks (writing, threading a needle) become impossible — not because the person can’t feel or see, but because the movement signals cannot be refined.
The cerebellum does NOT affect consciousness or sensation directly.
The medulla oblongata is the lowest part of the brainstem, transitioning into the spinal cord. It contains centres for the most critical automatic functions.
Vital centres in the medulla:
- Cardiac centre — regulates heart rate (via vagus nerve and sympathetic nerves)
- Vasomotor centre — controls blood vessel diameter, hence blood pressure
- Respiratory centre — controls rate and depth of breathing
- Reflex centres — swallowing, vomiting, coughing, sneezing, hiccupping
Damage to medulla → Life-threatening: Even partial damage can stop breathing or cardiac rhythm. This is why injuries to the back of the skull or upper spinal cord are so dangerous. A person in a coma can still breathe — because medullary centres work even when the cerebrum is not active.
| Region | Location | Initiates/Refines/Controls | Damage Effect |
|---|---|---|---|
| Cerebrum | Forebrain (top) | Thinking, voluntary actions, sensory perception | Specific loss depending on area affected |
| Cerebellum | Hindbrain (back) | Refines movement, balance | Ataxia — uncoordinated movement |
| Medulla | Hindbrain (bottom) | Vital autonomic functions | Can be fatal |
Why This Works
The brain is organised hierarchically — more critical (survival) functions are handled by the most ancient, deepest structures. The medulla represents evolutionarily old neural tissue present in fish, reptiles, and mammals alike. The cerebrum’s cortex is most developed in humans and great apes.
This hierarchy explains a key observation: in vegetative state (cerebrum non-functional), the patient still breathes and has a heartbeat — medullary centres are still active. In brain-dead patients, even medullary function has ceased — the person is maintained only by machines.
Alternative Method — Damage-Based Questions
NEET often gives you a scenario and asks which brain part is affected. Use this logic:
- Can’t balance/coordinate → cerebellum
- Can’t breathe independently → medulla
- Can’t speak/understand language → cerebrum (Broca’s/Wernicke’s area)
- Can’t see despite healthy eyes → occipital cortex
- Personality change, poor judgment → frontal lobe
NEET 2022 asked: “Which part of the brain is responsible for maintaining posture and equilibrium?” Answer: Cerebellum. NEET 2020: “Injury to medulla oblongata leads to?” Answer: Stoppage of heartbeat and breathing. These damage-based questions appear almost every year.
Common Mistake
Students confuse cerebrum with cerebellum because the names are similar. Remember: cerebrum is the larger structure (conscious thinking). Cerebellum means “little brain” — smaller, handles coordination. Also, don’t confuse medulla oblongata (brainstem) with adrenal medulla (inner part of adrenal gland that secretes adrenaline) — two completely different structures.