When Do Day-Night Circadian Rhythms Really Start for Infants?

Discussion The earth rotates on its axis approximately every 24 hours with corresponding changes in ambient light occurring over that time period. Circadian systems have evolved in almost all living organisms to adapt to the changes in environmental light conditions and include sleep-wake cycles and changes in daily hormone production. In mammals , “[c]ircadian clocks resident in nearly every, if not all, mammalian cells…” and have been detected in embryonic stem cells. The circadian timing system has 3 major components – a central biological clock, input pathways and output pathways. The central biological clock in the suprachiasmatic nuclei (SCN) isin the anterior hypothalamus just above the optic chiasm. There are peripheral biological clocks such as the liver also but they play less importance. The SCN oscillations (or rhythmic changes) are about 24 hours in length, but not exactly and stimulation is needed daily to reset the SCN and prevent it from drifting or freely running out of phase. Input pathways are mainly from light which strikes the retina sending messages directly to the SCN or from the retina to the retinohypothalmic tract and then to the SCN. Output pathways are to the hypothalamus and other nonhypothalamic sites that regulate the daily changes of several hormones including melatonin and cortisol, which are two of the most important hormonal circadian regulators. Melatonin is produced in the pineal gland. Melatonin is the main horm...
Source: PediatricEducation.org - Category: Pediatrics Authors: Tags: Uncategorized Source Type: news