endogenous pacemakers and exogenous zeitgebers

Question 1

what is an endogenous pacemaker

Answer 1

mechanisms within the body which governs the internal, biological bodily rhythms

Question 2

what is an exogenous zeitgeber

Answer 2

an environmental cue, such as light, that helps to regulate the biological clock within an organism

Question 3

give some examples of endogenous pacemakers

Answer 3

1) suprachiasmatic nuclei

2) the pineal gland

Question 4

explain how the suprachiasmatic nuclei acts as an endogenous pacemaker

Answer 4

1) a tiny cluster of nerve cells which lies in the hypothalamus
2) Neurons within the SCN randomly synchronise with each other, this is so target neurones in sites elsewhere in the body receive correctly times signals

3) the SCN receives signals from exogenous cues such as light via the optic nerve which reset the SCN internal circadian rhythm to match light levels

Question 5

explain how the pineal gland acts as an endogenous pacemaker

Answer 5

1) The SCN sends signals to the pineal gland causing increased production and secretion of the hormone melatonin at night and to decrease it as light levels increase
2) melatonin induces sleep by inhibiting brain mechanisms that promote wakefulness

Question 6

Give some examples of exogenous zeitgebers

Answer 6

1) light

2) social cues

Question 7

outline how light can be an exogenous zeitgeber

Answer 7

1) receptors in the SCN are sensitive to light changes and use this information to synchronise to activity of the body’s organs and glands
2) light resets the internal body clock each day

3) a protein called melanopsin found in retinal cells of the eye, is sensitive to light and carries signals to the SCN to set the daily body cycle

Question 8

outline how social cues can be an exogenous zeitgeber

Answer 8

1) research shows individuals are able to compensate for the absence of zeitgebers such as light by responding to social zeitgebers instead
2) research found that in cases of jetlag, going outside, where they were exposed to social cues, allowed them to adapt their circadian rhythms faster
3) likewise the circadian rhythms of blind people are seen to be the same as sighted people as both groups are exposed to the same social cues

Question 9

evaluate endogenous pacemakers

Answer 9

1) research for the role of the SCN using hamsters
2) use of animals limits ecological validity
3) dangers of disrupted rhythms= role of screens on melatonin levels reducing sleep, this could lead to cardiovascular disorders or mood disorders

Question 10

evaluate exogenous zeitgebers

Answer 10

1) support for the role of melanopsin= studies of blind individuals
2) case study of the role of light in French cave explorer
3) support for role of light= warm or blue-light