Summary Evaluation - Circadian Rhythms
Heart rate, metabolic rate, breathing rate and body temperature all reach maximum
values in the late afternoon/early evening and minimum values in the early hours of
the morning. If we reverse our sleep-waking pattern these rhythms persist. This
indicates human bodies are evolved for activity in the day and rest at night and,
indeed, being nocturnal or disrupting the circadian cycle is highly stressful and
physiologically and psychologically harmful.
The Endogenous Pacemaker controlling the sleep-waking cycle is located in the
hypothalamus. Patterns of light and darkness are registered by the retina, travel up
the optic nerves to where these nerves join (optic chiasma), and then pass into the
suprachiasmatic nucleus (SCN) of the hypothalamus. If this nerve connection is
severed circadian rhythms become random. The same effect is produced by
damaging the SCN of rats, and people born without eyes cannot regulate bodily
rhythms.
Circadian rhythms are primarily controlled by evolutionarily-determined, biological
structures that exert a strong influence on us to maintain normal sleep-waking
patterns.
Circadian rhythms are also influenced by Exogenous Zeitgebers ’s (EZ) - ‘cues’ in
the environment- about what time of day or night it is. In 1975 Siffre spent 6 months
underground in an environment completely cut off from all EZ’s. Although he
organised his time in regular patterns of sleeping and waking his body seemed to
have a preference for a 25 hour rather than a 24-hour cycle. This implies that
circadian rhythms are mainly controlled by EP’s rather than EZ’s.
If the sleep-waking cycle was primarily controlled by EZ’s they would tend to sleep a
huge amount in winter and hardly at all in summer. However, this is not the case -
they maintain a fairly regular pattern of sleeping and waking all year around.
Heart rate, metabolic rate, breathing rate and body temperature all reach maximum
values in the late afternoon/early evening and minimum values in the early hours of
the morning. If we reverse our sleep-waking pattern these rhythms persist. This
indicates human bodies are evolved for activity in the day and rest at night and,
indeed, being nocturnal or disrupting the circadian cycle is highly stressful and
physiologically and psychologically harmful.
The Endogenous Pacemaker controlling the sleep-waking cycle is located in the
hypothalamus. Patterns of light and darkness are registered by the retina, travel up
the optic nerves to where these nerves join (optic chiasma), and then pass into the
suprachiasmatic nucleus (SCN) of the hypothalamus. If this nerve connection is
severed circadian rhythms become random. The same effect is produced by
damaging the SCN of rats, and people born without eyes cannot regulate bodily
rhythms.
Circadian rhythms are primarily controlled by evolutionarily-determined, biological
structures that exert a strong influence on us to maintain normal sleep-waking
patterns.
Circadian rhythms are also influenced by Exogenous Zeitgebers ’s (EZ) - ‘cues’ in
the environment- about what time of day or night it is. In 1975 Siffre spent 6 months
underground in an environment completely cut off from all EZ’s. Although he
organised his time in regular patterns of sleeping and waking his body seemed to
have a preference for a 25 hour rather than a 24-hour cycle. This implies that
circadian rhythms are mainly controlled by EP’s rather than EZ’s.
If the sleep-waking cycle was primarily controlled by EZ’s they would tend to sleep a
huge amount in winter and hardly at all in summer. However, this is not the case -
they maintain a fairly regular pattern of sleeping and waking all year around.
