How Drugs Work Altering Mental Processes

A great many physical and mental disorders develop because of a malfunction in the nervous system. Some examples are Alzheimer s disease, schizophrenia, Parkinson s disease, Huntington s chorea, and bipolar disorder. Most of the effects produced by recreational drugs, such as alcohol, heroin, and cocaine, are also a result of changes in the way the nervous system functions. Today, scientists have a reasonably good understanding of the way in which the nervous system operates and how many types of chemicals affect this operation. 

In simple terms, messages travel along neurons (nerve cells) in the form of an electrical current that moves from one end of the neuron to its opposite end. The electric current is produced by a flow of sodium ions (Na ) and potassium ions (K ) across the nerve membrane, as shown in the diagram on page 11. When the electrical current reaches the end of the neuron, it causes the release of a chemical known as a neurotransmitter. Some examples of neurotransmitters are acetylcholine, serotonin, dopamine, GABA (gamma-aminobutyric acid), and norepinephrine. 

Neurotransmitters released at the end of one neuron travel the short distance between that neuron and another nearby neuron across a space known as the synaptie gap, shown in the diagram below. When the neurotransmitter reaches the second neuron, it bonds chemically to that structure, releasing a flow of electrical charges, which then travels down the second neuron. 

The key to nerve transmission—like most of the biochemical reactions that occur in living organisms—is the concept of a reeeptor molecule, a molecule to which some other molecule hinds. In the example just described, a receptor molecule is a specihc chemical compound with a distinctive shape into which the neurotransmitter molecule can fit. The diagram on page 12 shows how a specihc neurotransmitter has the correct shape to ht into a receptor molecule. 

However, a similar molecule with a different shape would he unahle to dock at the neurotransmitter molecule. 

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