The nervous system is a complex, sophisticated system that regulates and coordinates the body's basic functions and activities. It is made up of:
Central nervous system - consisting of the brain and spinal cord
Peripheral nervous system - consisting of all other neural elements

Psychiatry is the medical specialty devoted to the study and treatment of mental disorders. These mental disorders include various affective, behavioural, cognitive and perceptual abnormalities, producing either distress or impairment of function. The word psyche comes from the ancient Greek for soul or butterfly.
Common psychiatric disorders include

    • Schizophrenia Spectrum and Other Psychotic Disorders
    • Bipolar and Related Disorders
    • Depressive Disorders
    • Anxiety Disorders
    • Sleep-Wake Disorders
    • Substance Use and Addictive Disorders

Mental disorders are common. Worldwide more than one in three people in most countries report sufficient criteria for at least one at some point in their life. Anxiety disorders are the most common followed by mood disorders while substance disorders and impulse-control disorders were consistently less prevalent.

A review of anxiety disorder surveys found average lifetime prevalence estimates of 16.6%.

A review of mood disorder surveys in different countries found lifetime rates of 6.7% for major depressive disorder and 0.8% for Bipolar I disorder.

An international review of studies on the prevalence of schizophrenia found an average (median) figure of 0.4% for lifetime prevalence.

A European study found that approximately one in four people reported meeting criteria at some point in their life for at least one of the DSM-IV disorders assessed, which included mood disorders (13.9%), anxiety disorders (13.6%) or alcohol disorder (5.2%). Approximately one in ten met criteria within a 12-month period. Review of surveys in 16 European countries found that 27% of adult Europeans are affected by at least one mental disorder in a 12 month period.