Every thought and idea, every wish and want, every emotion and feeling, happens inside the brain. The brain fills the top half of the head, well protected within the domed skull bone. It looks like a large, wrinkled lump of pink-grey jelly. It contains some 50 billion nerve cells, or neurones. Each nerve cell is linked to many thousands of others. Tiny electrical nerve signals pass through this vast network, representing your thoughts and memories. Nerve signals also come into the brain from nerves all over the body, and go out to the muscles.
INSIDE THE BRAIN
The brain has four main parts. The brain stem at the base tapers into the spinal cord. It controls automatic bodily activities such as heartbeat, breathing and digestion. The mid-brain just above has close links with the hormone system. One of its parts, the thalamus, controls the level of awareness, from wide awake and alert to drowsy or asleep. The third part is the cerebellum, a wrinkled lump at the rear. It deals with muscle control to make movements smooth and coordinated. The fourth part is the cerebrum, where thinking happens.
NERVE CELLS AND SIGNALS
A nerve signal is a tiny pulse of electricity that travels very fast, almost 100 metres per second, along a nerve cell. A nerve cell has a normal-shaped cell body surrounded by thin, spidery parts called dendrites. It also has a very long, thin part like a wire, called the axon. Dendrites collect nerve signals from other nerve cells and pass them on, via the axon, to other nerve cells. Nerves contain bundles of hundreds or thousands of nerve cells.
The brain’s thoughts, ideas and memories consist of nerve signals flashing to and fro around the unimaginably vast network of billions of nerve cells. New connections between nerve cells are constantly being made as old ones are lost. A new memory may form as a new pathway or route around certain cells. If you recall this memory often, you “refresh” the pathway and keep it active. If not, the memory fades.
THE NERVOUS SYSTEM
The base of the brain merges into the spinal cord. The cord has nerve branches that reach out to everybody part, down to the fingertips and toes. The spinal cord carries nerve signals to and fro between the brain and all of these body parts. In addition, there are nerves that branch directly from the brain, into the head, face, neck and chest. These are cranial nerves.
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