Biological rhythms

what are biological rhythms

cyclical patterns of changes

what are the 3 types of biological rhythms

ultradian, circadian, infradian

ultradian rhythm

biological process that repeats more frequently than once every 24hrs (minutes/hours), e.g. stages of sleep

circadian rhythm

biological process that repeats approximately every 24hrs, e.g. sleep/wake cycle, core body temp

infradian rhythm

biological process that repeats less frequently than once every 24 hrs (weeks/months), e.g. menstrual cycle

what are endogenous pacemakers

internal body clocks

what is the main endogenous pacemaker in humans

suprachiasmatic nucleus (SCN) - cluster of neurons in the hypothalamus above the optic nerve, one in each hemisphere

what does the SCN do

sends signals to the pineal gland to increase production of melatonin at night - melatonin makes us sleep by inhibiting neural mechanisms that promote wakefulness

what are exogenous zeitgebers

environmental/external cues which affect our biological body clock

what is the main zeitgeber that affects our sleep/wake cycle

light

how does light affect out body clock

information from the retina goes to the SCN informing it of the amount of light received - decreased light levels cause SCN to increase melatonin secretion, increased light levels stimulates SCN to decrease melatonin secretion

what is another exogenous zeitgeber other than light

social cues like mealtimes or social activities can compensate for a lack of light

what is research support for SCN

Folkhard et al (1985) - studied people living in a bunker for 12 weeks, Ps went to bed when clock indicated 11:45pm and wake up at 7:45am, researchers quickened the clock so only 22 hours passed, volunteers cycle continued to follow the 24 hr clock instead of the 22 hr clock, SCN had more effect than the clock

what are animal studies supporting SCN affecting the sleep/wake cycle

• Stephan and Zucker damaged the SCN in rats, rats did not have the usual circadian pattern compared to rats with an intact SCN

• Morgan (1995) removed SCN from hamsters and found their sleep/wake cycle disappeared, it was reestablished by transplanting SCN cells from foetal hamsters

what is research support for social cues

Luce and Segal - people living in the Arctic circle still sleep around 7hrs a night even though the sun never sets during summer, in certain circumstances external cues take over and dictate sleeping times: supports theory that social cues affect our biological rhythm

research support for light being an exogenous zeitgeber

Campbell and Murphy - effect of light on sleep/wake cycle when light is detected by skin receptors, not by the eyes: Ps’ woken at various times and a light shone on the back of knees, found that there was a change in their usual sleep/wake cycle by up to 3 hrs, suggests that light is a powerful zeitgeber that doesn't need to rely on the eyes to influence the brain and affect the sleep/wake cycle