The central nervous system: brain and spinal cord
The brain and spinal cord form the central nervous system. The cerebrum thinks and controls voluntary actions, the cerebellum keeps balance, and the medulla runs involuntary actions.
How the brain and spinal cord are protected
- The brain lies inside a bony box, the cranium (brain box) of the skull.
- Three membranes, the meninges, cover the brain and continue over the spinal cord. They are the tough outer dura mater, the thin, web-like arachnoid and the inner pia mater, rich in blood vessels.
- The spaces between them hold cerebrospinal fluid, which works as a cushion against shocks.
- The spinal cord runs inside the neural canal of the backbone (vertebral column).
- Meningitis is a serious infection of the meninges by germs. It spreads through coughs, sneezes and shared utensils. Fever, a stiff neck, headache and eyes hurt by light are warning signs, so see a doctor at once. Vaccines can protect against it.
Parts of the brain and their jobs
| Part | Where and what it is like | Jobs |
|---|---|---|
| Cerebrum | The largest part: two halves (cerebral hemispheres) with a folded surface of ridges and grooves | Seat of intelligence, memory, reasoning, consciousness and will-power; controls all voluntary actions; helps us make well-thought-out decisions |
| Cerebellum | A smaller part below the back of the cerebrum, with many furrows | Keeps the balance of the body and coordinates muscles, for example in walking |
| Medulla oblongata | The lowest part, at the base of the skull; it continues as the spinal cord | Controls involuntary actions: heartbeat, breathing and the movement of food in the gut |
| Hypothalamus | A small part at the base of the brain, above the pituitary gland | Controls body temperature |
Cerebrum vs cerebellum
They work together. When you decide to walk, the order starts in the cerebrum; the cerebellum makes the many muscles work smoothly and on time. Alcohol upsets the cerebellum, which is why a drunk person walks clumsily.
The spinal cord: structure and jobs
- It runs from the medulla oblongata down almost the whole length of the backbone.
- Its gray matter (cell bodies of motor neurons) lies inside, and its white matter (axons) lies outside: the reverse of the brain.
- A small central canal filled with cerebrospinal fluid runs through it. The fluid cushions it and helps neurons exchange food, wastes and gases.
- Jobs: it controls reflexes below the neck. It carries sensory impulses from the skin and muscles up to the brain. It carries motor orders from the brain to the trunk and limbs.
Forebrain, midbrain and hindbrain
Some question papers divide the brain into three regions. The forebrain is mainly the cerebrum, with the hypothalamus. It is the thinking part and controls voluntary actions. The midbrain is a small part that connects the forebrain with the hindbrain. The hindbrain includes the cerebellum and the medulla oblongata. It keeps posture and balance and controls involuntary actions.
How to draw the human brain
- Draw a large, folded dome for the cerebrum, filling most of the space. Show its folds as wavy lines.
- Under the middle of the cerebrum, mark the small hypothalamus, with the pea-sized pituitary gland hanging below it.
- At the back, under the cerebrum, draw the smaller cerebellum, with fine lines for its furrows.
- In front of the cerebellum, draw the medulla oblongata, narrowing down into the spinal cord.
- Draw the skull around the brain, with a thin line under it for the meninges.
- Label each part, and write one job beside the cerebrum, the cerebellum and the medulla.
Wearing a helmet on a scooter or motorbike protects the skull, and the brain inside it, in a fall. Choosing a study stream or a career is a well-thought-out decision made by your cerebrum, so take your time and gather information.
2 marks: “Name the three membranes that cover the brain. What is the job of the cerebrospinal fluid?” Dura mater (outer), arachnoid (middle) and pia mater (inner). The fluid fills the spaces between them and cushions the brain against shocks.
3 marks: “Give one job each of the cerebrum, the cerebellum and the medulla oblongata.” Cerebrum: thinking, memory, intelligence and voluntary actions. Cerebellum: balance and coordination of muscles. Medulla oblongata: involuntary actions such as heartbeat and breathing.
5 marks: “Draw a labelled diagram of the human brain. Describe the jobs of its main parts and how the brain is protected.” Labelled diagram: cerebrum, cerebellum, medulla oblongata, spinal cord, hypothalamus, pituitary. Jobs of each part. Protection: skull, three meninges and cerebrospinal fluid.
Cerebrum is clever (thinking); cere-BELL-um rings the balance bell; medulla does the must-do jobs (heartbeat, breathing).