Circadian rhythms

What are circadian rhythms

• rhythms that last around 24 hours

• e.g. sleep wake cycle, core body temperature

2 things the body’s biological rhythms is governed by

• endogenous pacemakers- body’s internal clocks which regulate biological rhythms

• exogenous zeitgebers- changes in environment e.g. light

Sleep/wake cycle as example of circadian rhythm 

• its an example of a circadian rhythm- dictates when we should be asleep & awake

• Light is primary input, acts as external cue for sleeping/waking.

• Light detected by eye, which sends message about its brightness levels to SCN.

• SCN uses this info to control activity of circadian system

Research supporting circadian rhythms- Siffre et al (case study)

• spent 2 months in cave to see effects on his biological rhythm

• deprived external cues- exposure natural light and sound 

• he returned in September but he thought it was august. 

• found his biological clock was just beyond normal 24 hours but continued to sleep, eat regular. 

Research supporting circadian rhythms- Aschoff &Wever

• participants spent 4 week sin bunker deprived of natural light

• All but 1 showed circadian rhythms between 24-25 hours

• Suggests natural sleep cycle may be longer than 24 hours but is entrained by exogenous zeitgebers. 

Research going against Siffre- Czielser

• said Siffre wasn’t deprived from artificial light as he used dim lighting

• said this may alter participants circadian rhythm

• early studies may have been confounded by using artificial light  

Strength of research into circadian rhythms- real world application

• findings developed areas like shift work, jet lag, chronotherapy

• knowledge about body’s biological clock helps employers set shifts that work with workers natural rhythm to avoid fatigue

• led to reducing jet lag effects by adjusting light exposure, sleep time when travelling across time zones

• chronotherapy- timing of drug treatment is coordinated with body’s biological rhythm to maximise effects. 

Limitation of research into circadian rhythms- methodology 

Sleep/ wake determined by homeostasis- circadian rhythm

• when someone’s been awake for too long, homeostasis tells body to sleep cause of energy consumption.

• this homeostatic drive increases throughout day, reaches max in evening when people sleep

body temperature- circadian rhythm

• body temp is lowest in early morning and highest in early evening

Ao1 for circadian rhythms- NOT RESEARCH INTO 

• circadian rhytms

• examples of them- sleep/wake cycle, homeostasis, body temp