circadian rhythms endogenous pacemakers and exogenous zeitgebers

Question 1

what is a biological rhythm? why have rhythms evolved?

Answer 1

cyclical changes in the way biological systems behave - rhythms have evolved because the environment which organisms live in has cyclic changes such as day/night summer/winter

Question 2

what is a circadian rhythm?

Answer 2

pattern of behaviour that occurs all or recurs approximately every 24 hours and which is set and reset by environmental light levels

Question 3

examples of circadian rhythms

Answer 3

body temperature and hormone production

Question 4

what is the sleep wake cycle?

Answer 4

alternating states of sleep and waking that are dependent on the 24 hour circadian cycle

Question 5

what regulates biological rhythms?

Answer 5

endogenous pacemakers and exogenous zeitgebers

Question 6

what are endogenous pacemakers?

Answer 6

internal mechanisms that govern biological rhythms in particular the circadian sleep wake cycle

Question 7

what is the most important endogenous pacemaker?

Answer 7

the SCN

Question 8

what are exogenous zeitgebers?

Answer 8

environmental events responsible for resetting the biological clock of an organism

Question 9

examples of exogenous zeitgebers

Answer 9

• social cues such as meal time
• lights which is responsible for resetting the body clock each day keeping it on a 24 hour cycle

Question 10

process of the sleep wake cycle

Answer 10

1. When night falls like lessens
2. Tiny photo receptors in the eye pick up lessening light signals
3. Lessening light signals carried to the SCN - obtains info on light from the optic nerve.
4. SCN is located in the hypothalamus.
5. SCN informs pineal gland which produces melatonin - when light is detected pineal gland stop melatonin production
6. Melatonin causes us to become sleepy by inhibiting the brain mechanisms that make us feel awake.
7. Sleep/wake.

Question 11

case study siffre’s cave studies

Answer 11

• our internal circadian body clock is free running - it maintains a 24 hour cycle even in the absence of external cues such as light
• french caver siffre spent long periods of time in dark caves to examine the effects on the free running biological rhythms - two months in 1962 and six months in the 1970
• siffre’s free running circadian rhythm settled down to just above the usual 24 hours about 25 hours and he did have a regular sleep wake cycle