describe the person s potential range of reaction to the environment, but it takes the environment in order to maximize that reaction. Also because of gene/environmental interactions, there will be differences in what happens physically and mentally to identical twins. Identical twins have the same genetic makeup or the same genotype but, because of the influence of the environment, they can have slightly different appearances and can get different diseases. Fraternal twins are different. They come from different eggs and different sperm cells so they are essentially no more related than siblings. Do the genes affect more than just physical characteristics? According to research, yes, they do. Genes seem to be able to help to determine sexual orientation, personality traits, temperament, and even the propensity toward spirituality. Temperament affects a person s risk for schizophrenia and depression, which also seem to have genetic origins. With regard to many of these psychological disorders, however, the environment also plays a role.
PARTS OF THE NERVOUS SYSTEM The nervous system is very complex, but plays a huge role in psychology and psychiatry. It is for this reason that you need to study the different aspects of the anatomy and physiology of the nervous system. There are certain psychological diseases that have a large neurological influence so you need to understand just how the nervous system works. Like all systems of the body, the nervous system is made from cells. There are two major types of cells in the nervous system, divided broadly into neurons and glial cells. Neurons are the main functional cells of the nervous system. They are electrically active and send signals along processes called axons and dendrites that pass a message to other neurons so that the related parts of the nervous system can work together. Figure 5 shows the basic structure of a neuron:
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