circadian clock

Introduction

• endogenous timekeeping system with an intrinsic period of ~24.15 hours*

* in humans

Structure

• circadian clock oscillator is a molecular complex facilitating the circadian clock

Physiology

• the master circadian clock resides in the suprachiasmatic nucleus (SCN) of the hypothalamus
• the SCN orchestrates peripheral tissue clocks through behavioral, neuroendocrine, & autonomic outputs
• the primary zeitgeber (environmental time cue) is the light-dark cycle, detected by melanopsin-containing intrinsically photosensitive retinal ganglion cells that project to the SCN via the retinohypothalamic tract
  • these cells are most sensitive to short-wavelength (~480 nm, blue) light
    • they can entrain the SCN even in perceptually blind individuals

More general terms

• molecular clock

Components

• circadian clock oscillator