This section, “Psychiatric Disorders and Psycho-
logic Conditions,” presents an overview discussion
of mental health and mental illness and includes
entries about psychiatric disorders, psychologic
conditions, and their treatments. The section “The
Nervous System” contains overview discussion
and comprehensive entries about conditions that
affect cognition, memory, and thought processes
that arise from disease or injury to BRAINstruc-
tures that alters brain function.
Finding the Line between
Mental Health and Mental Illness
Psychiatric disorders and psychologic conditions
are those that doctors generally define as illnesses
that arise from disrupted thought processes and
their corresponding behaviors. However, the
causes of mental illness remain poorly under-
stood. Most psychiatric disorders reflect a mix of
biochemical, behavioral, and genetic components.
About 80 percent of people who have BIPOLAR DIS-
ORDER, for example, have other family members
who have either bipolar disorder or clinical
DEPRESSIONthat requires treatment.
The diagnosis of mental illness is often a signifi-
cant challenge. One issue is that many of the
symptoms that characterize mental illness are
thoughts, feelings, and behaviors that everyone
experiences to certain degree. However, in many
situations it is less the symptoms themselves and
more the level of dysfunction the symptoms cause
in the person’s life that defines the line between
mental health and mental illness.
For example, a person may sometimes engage
in speaking as though in conversation with
another person when no one else is in fact present
or talking, but knows the dialogue is a process of
thinking aloud and can willingly start and stop the
behavior. The behavior may appear amusing or
quirky to others but does not interfere with the
person’s ability to interact with other people and
to function in the world and thus in itself does not
constitute mental illness.
It is a different picture when a person engages
in dialogue with voices no one else can hear, but
believes the voices are real and thus cannot con-
trol his or her interactions with them. In such a
situation the person may believe the voices pro-
vide instruction or guidance, and behaves as
though following directions the voices give. The
messages from the voices may be nonsensical,
confusing, demanding, or demeaning to the per-
son and characteristically interfere with the per-
son’s ability to function in the world. This
behavior represents a clear break with reality and
interferes with the person’s ability to function in
the world and thus constitutes mental illness.The Diagnostic Path for
Psychiatric Disorders and Psychologic Conditions
The diagnostic path for mental illness begins with
the elimination of potential physical or physio-PSYCHIATRIC DISORDERS AND
PSYCHOLOGIC CONDITIONS
Psychiatry and psychology are disciplines within the practice of health care that deal with mental illness. Health-care
professionals who provide care for people who have mental illnesses include psychiatrists, who are physicians (MDs or
DOs); psychologists (PhDs); master’s level therapists such as counselors (sometimes also called psychologists); social
workers; and clinical registered nurse practitioners (CNRPs) who specialize in mental health. In the United States
licensing requirements and practice limitations for mental health practitioners vary among states, though in all states
only psychiatrists may prescribe medications.
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