... of most behaviourally active drugs can ultimately be traced to a direct or an indirect action on some aspect of the functioning of the nervous system. The source of power for the electrical activity of the nervous system comes from an uneven distribution of charged particles across the membranes of neurones. When an effective stimulus is applied to a neurone, local changes take place inside the membrane, which allows sodium ions to rush through the membrane. This influx of positive charge counteracts the negative resting potential and the cell becomes positively charged. As a result of the movement of charged particles, a wave of electrical activity travels down the axon. This controlled wave of change in the electrical charge that appears across the cell membrane is called the 'action potential'. As neurones are not in direct contact with each other nerve impulses pass from one neurone to another via specialised ...

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