Key terms

• Circadian rhythm- Biological rhythms that occur over a 24 hour cycle
• Biological rhythm- Patterns of changes in body activity over cyclical periods
• Ultradian rhythm- Biological rhythms that occur more than one cycle in 24 hours.
• infradian rhythm- Biological rhythms that occur less than one cycle in 24 hours.
• Endogenous pacemaker- Internal body clocks that regulate biological rhythms.
• Exogenous zeitgebers- External cues that influence our biological rhythms.