This work may not be copied, distributed, displayed, published, reproduced, transmitted, modified, posted, sold, licensed, or used for commercial purposes. By downloading this file, you are agreeing to the publisher’s Terms & Conditions.


The Human Circadian System in Normal and Disordered Sleep

Gary S. Richardson

Published: November 15, 2005

This CME activity is expired. For more CME activities, visit
Find more articles on this and other psychiatry and CNS topics:
The Journal of Clinical Psychiatry
The Primary Care Companion for CNS Disorders

Article Abstract

The human circadian system regulates rhythmicity in the human body and establishes normal sleep and wake phases. The suprachiasmatic nuclei (SCN), located in the hypothalamus above the optic chiasm, make up the human pacemaker known as the circadian or biological clock, but other essential parts of the circadian system include the pineal gland, retina, and retinohypothalamic tract. The importance of light in resetting the intrinsic human circadian cycle, the intrinsic period of which is slightly longer than 24 hours, ensures that the human cycle will stay entrained to the earth’s 24-hourdaily cycle. Within the SCN neurons, circadian rhythmicity is generated by the regular transcription of proteins. Since the circadian system is the foundation of the sleep-wake cycle, disorders and abnormalities in sleep are often connected with disorders or abnormalities in the circadian system. Circadian rhythm sleep disorders, such as jet lag syndrome and shift work sleep disorder, are those specifically attributed to dysfunctions or insufficiencies in the circadian system. Taking into consideration the preeminence of the circadian clock in timing sleep, it is likely that other sleep disorders, such as insomnia, are also linked to circadian system abnormalities.

Some JCP and PCC articles are available in PDF format only. Please click the PDF link at the top of this page to access the full text.

Volume: 7

Quick Links: