Endogenous pacemakers BP

Question 1

endogenous pacemakers

Answer 1

internal body clocks that regulate many of our biological rhythms, such as the influence of the suprachiasmatic nucleus SCN on the sleep/wake cycle

Question 2

exogenous zeitgeber

Answer 2

external factors that affect or entrain our biological rhythms, such as the influence of light on the sleep/wake cycle

Question 3

sleep/wake cycle

Answer 3

a daily cycle of biological activity based on a 24 hour period (circadian rhythm) that is influenced by regular variations in the environment, such as the alternation of night and day

Question 4

The suprachiasmatic nucleus SCN

Answer 4

• bundle of nerves
• located in the hypothalamus in each hemisphere of the brian.
• crucial in maintaining circadian rhythms.
• lies just above the optic chiasm
• received information about light directly from this structure.
• The biological clock is enabled as this continues even when our eyes are closed thus adjusting to changing patterns of daylight when we are asleep.

Question 5

DeCoursey et al

Answer 5

• Destroyed SCN connections in the brains of 30 chipmunks
• Returned them back to natural habitats
• Observed the for 80 days
• sleep/wake cycles of chipmunks disappeared and a significant proportion of them were killed by predators
• This is because they were awake and active when they should have been asleep

Question 6

Ralph et al

Answer 6

• Bred ‘mutant’ hamsters with 20 hour sleep/wake cycle
• When SCN cells of mutant hamsters were placed in brains of normal hamsters, cycles of second group defaulted to 20 hours

Question 7

The pineal gland and melatonin

Answer 7

The SCN passes information on day length and light to the pineal gland. This endogenous mechanism guides the sleep/wake cycle. During the night, melatonin production is increased by pineal gland.

Question 8

Light

Answer 8

Light can reset the SCN and thus plays a role in the maintenance of the sleep/wake cycle. Light also has an indirect influence on key processes in the body that control such functions as hormone secretion and circulation.

Question 9

light

Campbell and Murphy

Answer 9

• Light may be detected by skin receptors
• 15 participants were woken at various times with a light pad shone on their knees
• The researchers managed to disrupt their sleep/wake cycles by up to 3 hours
• Thus suggesting that light is a powerful exogenous zeitgeber

Question 10

social cues

Answer 10

• Newborn babies initial sleep/wake cycle is very random
• The circadian rhythm begins at around 6 weeks
• By 16 weeks the babies schedules have been entrained by the parents schedule
• Jet lag research suggests that appealing to meal and sleep times of the country you are in is an effective ebay to entrain your circadian rhythm

Question 11

beyond the master clock

edogenous pacemaker and the sleep wake cycle limitation

Answer 11

May obscure other body clocks
* There are numerous circadian rhythms in many organs and cells called peripheral oscillators
* Damiola et al demonstrated how changing feeding patterns in mice could alter the circadian rhythms in liver cells by 12 hours
Other complex influences on the sleep/wake cycle

Question 12

Interactionist system

edogenous pacemaker and the sleep wake cycle limitation

Answer 12

Endogenous pacemakers cannot be studied in isolation
* Total isolation studies like Siffre’s cave study are extremely rare
* In everyday life, pacemakers and zeitgebers interact
The more researchers attempt to isolate the influence of internal pacemakers, the lower the validity of the research.

Question 13

environmental observation

Exogenous zeitgebers and the sleep/wake cycle limitation

Answer 13

Exogenous zeitgebers do not have the same effect in all environments
* Those who experience little darkness in summer and little light in winter are an anomaly
* Eg people who live in arctic circle have similar sleep patterns all year despite spending 6 months in darkness
Therefore the sleep/wake cycle is primarily controlled by endogenous pacemakers

Question 14

case study evidence

Exogenous zeitgebers and the sleep/wake cycle limitation

Answer 14

Evidence challenges role of exogenous zeitgebers
* Miles et al recounted the study of a blind man who had an unusual circadian rhythm of 24.9 hours
* Despite exposure to social cues his rhythm could not be adjusted
Social cues alone are not effective in resetting the biological rhythm