The brain and the spinal cord make up the central nervous system. The forebrain thinks and controls voluntary actions; it also has the hunger centre. The midbrain and the hindbrain control involuntary actions: the medulla controls blood pressure, salivation and vomiting, and the cerebellum keeps balance. The skull, a fluid and the backbone protect them. Nerve impulses make muscles contract.
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The central nervous system
The brain and the spinal cord together make the central nervous system. They receive messages from all over the body, and send messages out.
Nerves from the brain and the spinal cord reach every part of the body. These nerves make the peripheral nervous system. Some carry messages in, and some carry them out.
The brain is the main coordinating centre. It lets us think and make decisions based on what we sense. It also controls many actions that happen without our deciding.
Voluntary and involuntary actions
A voluntary action is one that we decide to do: writing, talking, kicking a ball, choosing a book.
An involuntary action happens without our deciding: the heartbeat, breathing, the watering of the mouth at the smell of food.
Some involuntary actions are reflexes, handled by the spinal cord. Others are controlled by parts of the brain.
The three parts of the brain
The human brain seen from the side, with the front to the left, inside the curve of the skull. The large cerebrum fills the top and is part of the forebrain; it does thinking, feeling through the senses and voluntary actions. Below it sit the small hypothalamus, also forebrain, and the midbrain. Below the midbrain are the pons and the medulla of the hindbrain; the medulla controls blood pressure, salivation and vomiting. Behind them at the back is the cerebellum of the hindbrain, which keeps balance and posture. The spinal cord runs down from the medulla.
The forebrain is the main thinking part.
The cerebrum is its largest part. It has areas that receive messages from the eyes, ears, nose, tongue and skin.
Other areas join this information with what we remember, and decide what to do.
It sends messages to the muscles for voluntary actions.
The forebrain also has a hunger centre, which tells us when we are hungry.
The midbrain and the hindbrain control many involuntary actions.
The medulla, in the hindbrain, controls blood pressure, salivation and vomiting.
The pons, also in the hindbrain, helps to control breathing.
The cerebellum, at the back of the hindbrain, keeps posture and balance. It makes voluntary actions precise: walking in a straight line, riding a bicycle, picking up a pencil.
How the brain and the spinal cord are protected
The brain and the spinal cord are delicate, so the body guards them well.
The brain sits inside a bony box, the skull (cranium).
Inside the skull, the brain floats in a fluid, which cushions it against shocks.
The spinal cord runs inside the vertebral column, the backbone.
How nerves make muscles move
A muscle moves when its cells change shape. When an impulse reaches a muscle cell, special proteins inside the cell change their shape and arrangement. The cell becomes shorter, and the muscle contracts. When the impulses stop, the muscle relaxes.
The brain is a busy organ. It is only about a fiftieth of the body's mass, but at rest it uses about a fifth of the body's energy.
Try it in Python
The program lists six actions, the part of the brain that controls each, and whether the action is voluntary.
You should see that 3 of the 6 actions are voluntary. Both medulla actions are involuntary.
Practise with new numbers
Common mistakes
Giving balance to the cerebrum. Balance and posture belong to the cerebellum.
Thinking the brain controls only what we decide. The medulla controls many involuntary actions.
Forgetting the fluid. The skull is not the only protection; the fluid cushions the brain.
Thinking muscles move on their own. A muscle contracts when nerve impulses reach it.
Remember these
The brain and the spinal cord form the central nervous system.
The forebrain thinks, senses, controls voluntary actions and has the hunger centre.
The medulla controls blood pressure, salivation and vomiting; the cerebellum keeps balance.
The skull, a fluid and the vertebral column protect the brain and the spinal cord.
Impulses make proteins in muscle cells change shape, so the muscle contracts.
Check yourself
Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.
Which part of the brain is damaged if a person cannot walk in a straight line?
Name two involuntary actions controlled by the medulla.
Is writing your name a voluntary or an involuntary action? Which part of the brain sends the messages?
Name the three things that protect the brain and the spinal cord.
What happens inside a muscle cell when an impulse reaches it?
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