AO1 - Circadian Rhythms

• A cycle that lasts for 24 hours, e.g. sleep wake cycle
• One example of a circadian rhythm is the sleep wake cycle which is mainly controlled by the master endogenous pacemaker, the SCN found in the hypothalamus (brain)
• 1. When it goes dark, our eyes detect a change in light (exogenous zeitgeber)
• 2. This change in light activates the SCN in the hypothalamus (endogenous pacemaker) - this stimulates the pineal gland to release melatonin and promote sleep
• 3. When it turns to morning and our eyes detect the light (exogenous zeitgeber), the SCN is reset which maintains the sleep wake cycle so we can be in sync with the outside world