pacemakers + exogenous

• Biological rhythms are influenced by two things: internal body clock and external cues
• Endogenous pacemakers are internal body clocks
• Exogenous zeitgebers are external cues in the environment
• An example of an endogenous pacemaker is the influence of the superchiasmatic nucleus (SCN) on the sleep/wake cycle
• An example of an exogenous zeitbergers is the influence of light on the sleep/wake cycle