Biological Rhythms

Biological Rhythms- Any change in a biological activity which occurs regularly usually divided into daily, monthly or yearly cyclical changes in the environment.

Infradian Rhythm- Less than once every 24hrs e.g Menstrual Cycle OVER 24HRS

Ultradian Rhythm- More than once every 24hrs e.g Sleep Stages UNDER 24HRS

Circadian Rhythm- 24hr cycle e.g Sleep/Wake Cycle LASTS 24HRS

Exogenous Zeitgebers- External factors that influence biological rhythms e.g light

Endogenous Pacemaker- Biological clocks which are influenced by exogenous zeitgebers. regulates rhythms within the body.

Supachaismatic Nucleus (SCN)- In the hypothalmus it monitors light levels in the optic nerve.

Melatonin- A hormone secreted by the Pineal Gland. In the presence of light, levels are low but during the night levels increase.