Mental, or psychological, illnesses and disorders occur in or relate to the mind. Mental disorders differ from physical (related to the body) disorders because there are usually no physical symptoms of a mental disorder (such as a broken arm or an upset stomach) for a doctor to observe. Mental disorders originate in the mind of an individual and display themselves outwardly through a person's behavior or emotions. When behavior or emotions are deemed "abnormal," a mental illness might be at the root of the problem.
In a world in which cultural and social differences are abundant, particularly as one moves from one country or region to another, it is very difficult to define what is "normal" behavior over what is "abnormal" behavior. However, abnormal behavior has come to be identified through the presence of different coexisting characteristics or conditions:
Infrequency is one facet of abnormal behavior; in other words, a behavior or characteristic exhibited or not exhibited by the majority of people determines normalcy. Another hallmark of abnormal behavior is whether or not the behavior violates social norms; this will differ from culture to culture and therefore allows for a range of differences in behavior. This can present difficulties in definition because while many criminals violate social norms, they are not always deemed to be mentally ill. Another way of identifying abnormal behavior is personal distress and the degree of an individual's suffering. For example, does a person's grief over something fall outside the scope of what is a "normal" level of grief or is it exceeding the average time it takes for an individual to recover from the grief?
Disability and dysfunction are also used to assess an individual's well-being. For example, someone with a great but irrational fear of something might not be able to participate in daily activities or may be experiencing a great deal of personal distress because of this fear. Finally, another factor in determining abnormality of behavior is whether someone's response to a situation is unexpected. For example, thirst is an expected response to not drinking enough fluids, but becoming emotionally distraught over thirst would not be an expected response.
This chapter describes a variety of major mental conditions and disorders. Some are deep-rooted mental illnesses, such as schizophrenia; others are more easily treatable, such as a learning disorder. Most mental disorders are treatable and, like many physical disorders, mental illness is not the result of something a person has or has not done to influence its development. Mental illness, like physical disease, can and does strike people from all walks of life. However, just as medical treatment for physical ailments has improved markedly over time, so has the diagnosis and treatment of mental illness.