The internal and external influences on sleep

In this lesson you will learn about bodily or bio-rhythms, which can be described as changes in hormone levels, blood pressure and temperature, for example, that follow a predictable pattern over a set time period.

You need to know about circadian rhythms, where a full cycle takes 24 hours and ultradian rhythms, where there is more than one cycle in a 24 hour period.

An example of a circadian rhythm would be the sleep-wake cycle.

An example of an ultradian rhythm would be the sleep stages.

Circadian Rhythms

Ultradian Rhythms

Zeitgebers – Light

You will also learn about a hormone called melatonin which is released from the pineal gland. Melatonin is sometime called ‘nature’s sleeping draught’ meaning it is a chemical that is naturally produced in the brain which helps us to fall asleep.


Pineal gland


The following PowerPoint can be used for online teaching, once students have read up from the textbooks about the concepts and studies relating to this topic. To access the interactive elements it must be opened in google slides and you will need to the free pear deck add-on.