35.17: Nervous System Disorders - Neurodevelopmental Disorders - Mental Illnesses

Learning Objectives

• Distinguish between the disorders of schizophrenia and depression

Mental illnesses are nervous system disorders that result in problems with thinking, mood, or relating with other people. These disorders are severe enough to affect a person’s quality of life and often make it difficult for people to perform the routine tasks of daily living. Debilitating mental disorders plague approximately 12.5 million Americans (about 1 in 17 people) at an annual cost of more than $300 billion. There are several types of mental disorders including schizophrenia, major depression, bipolar disorder, anxiety disorders, post-traumatic stress disorder, and many others. The American Psychiatric Association publishes the Diagnostic and Statistical Manual of Mental Disorders (or DSM), which describes the symptoms required for a patient to be diagnosed with a particular mental disorder. Each newly-released version of the DSM contains different symptoms and classifications as researchers learn more about these disorders, their causes, and how they relate to each other. A more detailed discussion of two mental illnesses, schizophrenia and major depression, is given below.

Schizophrenia

Schizophrenia is a serious and often-debilitating mental illness affecting one percent of the population in the United States. Symptoms of the disease include the inability to differentiate between reality and imagination, inappropriate and unregulated emotional responses, difficulty thinking, and problems with social situations. Symptoms of schizophrenia may be characterized as either “negative” (deficit symptoms) or “positive”. Positive symptoms are those that most individuals do not normally experience, but are present in people with schizophrenia. They can include delusions, disordered thoughts and speech, and tactile, auditory, visual, olfactory and gustatory hallucinations, typically regarded as manifestations of psychosis. Negative symptoms are deficits of normal emotional responses or of other thought processes, and commonly include flat or blunted affect and emotion, poverty of speech, inability to experience pleasure, lack of desire to form relationships, and lack of motivation.

Many schizophrenic patients are diagnosed in their late adolescence or early 20s. The development of schizophrenia is thought to involve malfunctioning dopaminergic neurons and may also involve problems with glutamate signaling. Treatment for the disease usually requires anti-psychotic medications that work by blocking dopamine receptors and decreasing dopamine neurotransmission in the brain. This decrease in dopamine can cause Parkinson’s disease-like symptoms in some patients. While some classes of anti-psychotics can be quite effective at treating the disease, they are not a cure; most patients must remain medicated for the rest of their lives.

Figure \(\PageIndex{1}\): Schizophrenia: The development of schizophrenia is thought to be caused by malfunctioning dopaminergic neurons, which causes brain dysfunction and an imbalance of chemicals in the brain.

Depression

Major depression (also referred to as just “depression” or “major depressive disorder”) affects approximately 6.7 percent of the adults in the United States each year and is one of the most common mental disorders. To be diagnosed with major depressive disorder, a person must have experienced a severely-depressed mood lasting longer than two weeks along with other symptoms that may include a loss of enjoyment in activities that were previously enjoyed, changes in appetite and sleep schedules, difficulty concentrating, feelings of worthlessness, and suicidal thoughts. The exact causes of major depression are unknown and probably include both genetic and environmental risk factors. Some research supports the “classic monoamine hypothesis,” which suggests that depression is caused by a decrease in norepinephrine and serotonin neurotransmission. One argument against this hypothesis is the fact that some antidepressant medications cause an increase in norepinephrine and serotonin release within a few hours of beginning treatment, but clinical results of these medications are not seen until weeks later. This has led to alternative hypotheses. For example, dopamine may also be decreased in depressed patients, or it may actually be an increase in norepinephrine and serotonin that causes the disease, and antidepressants force a feedback loop that decreases this release.

Treatments for depression include psychotherapy, electroconvulsive therapy, deep-brain stimulation, and prescription medications. Most commonly, individuals undergo some combination of psychotherapy and medication. There are several classes of antidepressant medications that work through different mechanisms. For example, monoamine oxidase inhibitors (MAO inhibitors) block the enzyme that degrades many neurotransmitters (including dopamine, serotonin, norepinephrine), resulting in increased neurotransmitter in the synaptic cleft. Selective serotonin reuptake inhibitors (SSRIs) block the reuptake of serotonin into the presynaptic neuron. This blockage results in an increase in serotonin in the synaptic cleft. Other types of drugs, such as norepinephrine-dopamine reuptake inhibitors and norepinephrine-serotonin reuptake inhibitors, are also used to treat depression.

Key Points

• Complications with thinking, mood, or problems relating to other people are issues that are commonly associated with those affected with neurodevelopmental disorders.
• Malfunctioning dopaminergic neurons and problems with glutamate signaling are thought to be potential causes of schizophrenia.
• Although no definitive answer yet exists, genetic and environmental risk factors are believed to be the main causes of depression.
• Exact cures do not exist for either schizophrenia or depression; however, schizophrenia may be treated with anti-psychotic medications while depression treatments include psychotherapy, electroconvulsive therapy, deep-brain stimulation, and prescription medications.

Key Terms

• norepinephrine: a neurotransmitter found in the locus coeruleus which is synthesized from dopamine
• serotonin: an indoleamine neurotransmitter that is involved in depression, appetite, etc., and is crucial in maintaining a sense of well-being, security, etc.
• mental disorder: any of the various diseases affecting the mind onset by brain damage or genetics
• schizophrenia: a psychiatric diagnosis denoting a persistent, often chronic, mental illness variously affecting behavior, thinking, and emotion
• depression: in psychotherapy and psychiatry, a period of unhappiness or low morale which lasts longer than several weeks and may include ideation of self-inflicted injury or suicide
• dopamine: a neurotransmitter associated with movement, attention, learning, and the brain’s pleasure and reward system