ABSTRACT
The human brain is the most complex system known in the universe. There are over 10 billion nerve cells or neurons, each of which connects to 10 thousand others to form the systems and pathways that govern all our mental functions-mood, memory, sleep, dreaming for example and consciousness itself (Figure 1). Each neuron contains a particular transmitter —the chemical signal that is released when the neurons fire interacting with specific receptors so allowing the neurons to com municate with each other (Figure 2). There are over 50 of these chemical signals, which include glutamate, γ-aminobutyric acid (GABA), acetylcholine, noradrena line, dopamine and serotonin. The glutamate and GABA signals are the principal excitatory and inhibitory transmitters which “drive” the system. Superimposed on this framework are the modulatory transmitters which govern the mode of the system. Acetylcholine for example is concerned with attention, memory and dream ing, noradrenaline is concerned with arousal and responding to threatening or exciting stimuli, dopamine is concerned with drive, motivation and pleasure, and serotonin or 5-HT is thought to be concerned with mood.
