Medical Q&A #9 - The Brain And Nervous System

Common question.

My son boasted recently that he is clever because he has 20 thousand million cells in his brain. He is bright, but do we really have that many?


Yes, we do, and the latest estimates push the total even higher,possibly as high as 100 thousand million. Nevertheless, the heart of the system remains the single neurone, or nerve cell. Bundles of neurones make up a nerve, which is much like a telephone cable. Message flash from neurone to neurone by virtue of a complex electrochemical process, Neurones that carry messages to the central nervous system (the brain and the spinal cord) are called sensory neurones; those that carry messages from the central nervous system to muscles and other tissues, causing them to move and react, are called motor neurones. A single nerve may contain both sensory and motor neurones.

You might think of a neurone as a kind of electronically illuminated road that leads to the bank of a river, on the other side of which lies another road, another neurone. To get a message across the river, from one neurone to the next, chemical 'ferries' are required. If the nervous system is healthy, millions of chemical ferries constantly cross the gaps between neurones,carrying sensations and instructions to and from the central nervous system, all at the speed of light  - muscles move, events in the enviroment are felt, some of the events are stored away as memories. Part of this, activity is under your control (the hand grasps something by 'command'); part of it is automatic and not under your control  (the heart beats without conscious urging). Clearly, if any part of the nervous system is damaged or breaks down, the consequences can be serious and widespread. Muscles may weaken or cease functioning, events in the outside world may not be detected, memories may be wiped away.