Endogenous pacemakers and the sleep/wake cycle AO1

Question 1

what are endogenous pacemakers? (endogenous pacemakers and the sleep/wake cycle)

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
• the SCN is one of the primary endogenous pacemakers in mammalian species (including humans)
• its influential in maintaining circadian rhythms such as the sleep/wake cycle
• nerve fibers connected to the eye cross in an area called the optic chains on their way to the left and right visual area of the cerebral cortex

Question 2

what is the suprachiasmatic nucleus? (endogenous pacemakers and the sleep/wake cycle)

Answer 2

• a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain
• it is one of our primary endogenous pacemakers in mammalian species and is influential in maintaining circadian rhythms such as the sleep/wake cycle.
• nerve fibers connected to the eye cross in an area called the optic chasm on their way to the left and right visual area of the cerebral cortex.
• the SCN lies just above the optic chasm.
• it receives info about light directly from this structure. This continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep

Question 3

explain the influence of animal studies and the SCN (endogenous pacemakers and the sleep/wake cycle)

Answer 3

DeCoursey et al. (2000) destroyed the SCN connections in the brains of 30 chipmunks who were then returned to their natural habitat and observed for 80 days
- the sleep/wake cycle of the chipmunks disappeared and by the end of the study a significant proportion of them had been killed by predators (presumably because they were awake,active and vulnerable to attack when they should’ve been asleep)
- in another study, Ralph et al. (1990) bred ‘mutant’ hamsters with a 20- hour sleep/wake cycle. When SCN cells from the foetal tissue of mutant hamsters were transplanted into the brains of normal hamsters, the cycles of the second group defaulted to 20 hours.

Question 4

explain the role of the pineal gland and melatonin (endogenous pacemakers and the sleep/wake cycle)

Answer 4

The SCN passes the information on day length and light that it receives to the pineal gland. This is another endogenous mechanism guiding the sleep/wake cycle.
- During the night, the pineal gland increases production of melatonin- a chemical that induces sleep and is inhibited during periods of wakefulness.
- Melatonin has also been suggested as a causal factor in seasonal affective disorder.

Question 5

what are exogenous zeitgebers?

Answer 5

• are external factors in the environment that reset our biological clocks through a process known as entrainment.
• In the absence of external cues, the free-running biological clock that controls the sleep/wake cycle continues to ‘tick’ in a distinct cyclical pattern. This free-running cycle is then ‘brought into line’ by environmental cues, so there is an interaction of internal and external factors.

Question 6

give two examples of exogenous zeitgebers

Answer 6

light
- it can reset the body’s main endogenous pacemaker, the SCN, and thus plays a role in the maintenance of the sleep/wake cycle
- has an indirect influence on hormone secretion and blood circulation
- Scott Campbell and Patricia Murphy (1998) demonstrated that light may be detected by skin receptor sites on the body even when the same information is not received by the eyes.
- 15 participants were woken at various times and a light pad was shone on the back of their knees. The researchers managed to produce a deviation in the participants usual sleep/wake cycle of up to three hours in some cases. Suggesting light is a powerful exogenous zeitgeber that need not necessarily rely on the eyes to exert its influence on the brain.

Question 7

explain why social cues are an example of exogenous zeitgebers and the sleep/wake cycle.

Answer 7

• babies have the same sleep cycles usually as parents as they have imposed it on them.
• research on jet lag suggests that adapting to local times for eating and sleeping is an affective way of entraining circadian rhythms and beating jet lag when travelling long distances.