The receptor role

Enzymes are one major target for drugs. Receptors are another. Drugs which interact with receptors are amongst the most important in medicine and provide treatment for ailments such as pain, depression, Parkinson s disease, psychosis, heart failure, asthma, and many other problems. 

Cells are all individual, but in a complex organism such as ourselves, they have to get along with their neighbours. There has to be some sort of communication system. After all, it would be pointless if individual heart cells were to contract at different times. The heart would then be a wobbly jelly and totally useless in its function as a pump. Communication is essential to ensure that all heart muscle cells contract at the same time. The same holds true for all the body s organs and functions. Communication is essential if the body is to operate in a coordinated and controlled fashion. 

Therefore, there has to be a way of carrying the message across the gap between the nerve ending and the cell. The problem is solved by the release of a chemical messenger (neurotransmitter) from the nerve cell (Fig. 5.2). Once released, this 

We shall consider these secondary effects and how they result in a biological action at a later stage, but for the moment the important thing to note is that the communication system depends crucially on a chemical messenger. Since a chemical process is 

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