Endogenous Pacemakers and Exogenous Zeitgebers.

EPs have to coordinate with EZs to coordinate rhythms with the outside world.

The most important EP in the brain is the Pineal gland.

It contains light receptors which external light reaches by passing through a thin layer of skull.

These receptors influence activity of neurones in the Pineal gland. They convert serotonin into melatonin.

Melatonin manufacture is regulated directly by the amount of light. Melatonin decrease and serotonin increases as the sun goes down.

This means that waking is adjusted to the time the morning begins, which changes through the year.

The Suprachiasmatic Nucleus (SCN).

This is the main biological clock, located in the hypothalamus. The neurones here have an in-built circadian rhythm. 

The SCN regulates manufacture and secretion of melatonin in the Pineal gland via a connecting pathway. It is also connected to the retina, so light can influence the SCN neurones.

Research.

Campbell and Murphy…