[The brain's biological clock]

Abstract

Daily biological rhythms are controlled by a clock system, composed of a hierarchical multi-oscillator structure. Each cell in this system harbours a self-sustained autonomous molecular oscillator. Light adjusts the phase of the brain oscillator to the environmental light/dark cycle by intrinsically photosensitive retinal ganglion cells through their own photoreceptor, melanopsin, and by using the neuropeptide called pituitary adenylate cyclase-activating polypeptide as well as glutamate as neurotransmitters. The circadian synchronisation system is critical to health, and breakdown of the 24-hour temporal order could lead to pathological conditions.