Circadian Rythms

Question 1

Circadian rhythms

Answer 1

– Any cycle that lasts about 24 hours
– A pattern of behaviour that occurs/reoccurs every 24 hours which is set and reset by environmental light levels
– The word circadian - circa (about) dies (a day)

– Optimise an organism’s physiology and behaviour to best meet the varying demands of the day/night cycle

Question 2

Biological rhythms

Answer 2

Our bodies have several biological rhythms, these are repeating patterns of changes that occur in over a set periods of time. Some of these rhythms are daily, called circadian, some are more frequent than this, ultradian, some are less frequent, called infradian.

It is thought that all biological rhythms are maintained through a combination of exogenous zeitgebers (external cues) and endogenous pacemakers (our body clock). While our biological clock regulates our rhythms through various hormones and parts of the brain, these are regulated and reset by external factors such as natural light, to keep our ‘day’ to 24 hours, or meal times that ‘set’ our body clock.

Question 3

Endogenous pacemakers

Answer 3

The body’s internal body clocks that regulate biological rhythms e.g. suprachiasmatic nucleus - detects light, even when eyes are closed. Bundle of nerves in hypothalamus Influences sleep/wake – and other circadian
Gets info from optic nerve about light/dark, so bio clock can adjust to changing patterns of daylight

The SCN causes the Pineal Gland to release melatonin when the optic nerve reduces its activity as night falls. Melatonin reduces brain activity and so we become sleepy. The reverse happens when daylight begins i.e. SCN picks up light, signals the Pineal gland=melatonin production stops we wake up.

Question 4

Exogenous zeitgeibers

Answer 4

External factors in the environment which reset our biological clocks e.g. light, social cues

Question 5

Siffre

Answer 5

In 1962, a French speleologist named Michel Siffre spent two months living in total isolation in a subterranean cave, without access to clock, calendar, or sun.
Sleeping and eating only when his body told him to, his goal was to discover how What is a
the natural rhythms of human life would be affected by living “beyond time.”

After a 2 month cave stay, he then lived in a cave for 7 months! His findings were:
– He settled into a sleep/wake cycle of 25 to 30 hours - usually just beyond the usual 24 hour cycle
“My sleep was perfect! My body chose by itself when to sleep and when to eat.”
– Supports the assumption that endogenous pacemakers exert an influence on circadian rhythms
– showing the strength of the circadian rhythm as a free-running cycle and questions the extent to which it can be overridden by exogenous zeitgebers.

Question 6

Shift work

Answer 6

– Given researchers a better understanding of the adverse consequences that can occur due to disruption.
– Shift workers experience a period of reduced concentration (circadian trough) at around 6 in the morning making mistakes more likely.
– Researchers suggested a correlation between shift work and poor health- shift workers are 3 times more likely to develop heart disease.
– Economic implications in terms of how to manage worker productivity.