The brain is the pacemaker of the human body. If this pacemaker does not function life is not possible. In the brain there are more than 10 billion neurons. Each neuron makes more than a thousand contacts. The axons of the neuron branches ramify into several end terminals which are in contact with other cell bodies and dendrites. The propagation of the impulse is electric in the axons and the dendrites; in the synaptic cleft, however, the impulse is propagated via a neurotransmitter. This highly effective chemical substance is released from the terminal and stimulates a postsynaptic receptor. The neurons, the axons, and the dendrites are embedded in lipid membranes and are therefore difficult to influence by chemical drugs. However, in the synaptic cleft the propagation of the nerve impulse is more open for manipulation. This is a part of the brain where chemical drugs can easily influence the brain function. Most of the psychotropic drugs used at present have effects at the synaptic level on the metabolism, on the release and the reuptake of neurotransmitters, and on the receptors.