effect of endogenous pacemakers and exogenous zeitgebers on the sleep/ wake cycle.

Question 1

endogenous pacemakers

Answer 1

Internal body clocks that regulate many of our biological rhythms.

Question 2

exogenous zeitgebers

Answer 2

External cues that may affect our biological rhythms.

Question 3

biological rhythms

Answer 3

Biological rhythms must be constantly fine-tuned in order to stay in tune with the external world. In order to achieve this we have endogenous pacemakers, sometimes referred to as biological clocks, and exogenous (or external) zeitgebers, which reset this clock every day to maintain its coordination with the external world.

Question 4

the SCN

Answer 4

A tiny bundle of nerves, located in the hypothalamus. It is one of the primary endogenous pacemakers in mammals. It receives information about light and continues even when our eyes are closed. This allows the biological clock to adjust to changing patterns of daylight whilst we are asleep.

Question 5

SCN on sleep/wake cycle

Answer 5

The SCN sends signals to the pineal gland (located just behind the hypothalamus), directing it to increase production and secretion of the hormone melatonin at night and to decrease it as light levels increase in the morning. Melatonin induces sleep by inhibiting the brain mechanisms that promote wakefulness. The pineal gland and the SCN work together as endogenous pacemakers in the brain.

Question 6

entraining

Answer 6

Exogenous zeitgebers are environmental events that reset our biological clocks through a process known as entraining. The most important zeitgeber for most animals is light.
Social cues (such as mealtimes and social activities) are another example of exogenous zeitgebers.

Question 7

light

Answer 7

Receptors in the SCN are sensitive to changes in light levels during the day and use this information to synchronise the activity of the body’s organs and glands. Light resets the internal biological clock each day, keeping it on a 24 hour cycle. A small number of retinal cells contain melanopsin (a protein that is sensitive to natural light) and carry signals to the SCN to set the daily body cycle.

Question 8

AO3

Answer 8

Exogenous zeitgebers do not have the same effect in all environments. People who live in the Arctic Circle have similar sleep patterns all-year round, despite spending around six months in almost total darkness. However, researchers showed that individuals are able to compensate for the absence of zeitgebers such as natural light by responding to social zeitgebers instead.

Question 9

AO3

Answer 9

One of the earliest studies on jet lag from researchers found that the circadian rhythms of air travellers adjusted more quickly if they went outside more at their destination. This was thought to be because they were exposed to the social cues (such as mealtimes and social activities) of their new time zone, which acted as a zeitgeber.

Question 10

AO3

Answer 10

Studies have suggested that exogenous factors may be more responsible for the changes in sleep patterns amongst older people. Researchers found that the management of insomnia was improved if elderly people were generally more active and had more exposure to natural light.