Endogenous pacemakers and exogenous zeitgebers

Question 1

What does endogenous mean

Answer 1

Anything whose origins are within the organism

Question 2

What is the most important pacemaker in humans

Answer 2

The Suprachiasmatic nucleus

Question 3

Where is the Suprachiasmatic nucleus

Answer 3

In the hypothalamus

Question 4

What does the Suprachiasmatic nucleus do

Answer 4

Acts as the ‘master clock’ with links to other brain regions that control sleep and arousal, and has control over other biological clocks throughout the body

Question 5

How does the Suprachiasmatic Nucleus work

Answer 5

Neurons within the Suprachiasmatic nucleus spontaneously synchronise with one another, so that target neurons in other locations in the body receive correctly time-controlled signals

Question 6

How is the Suprachiasmatic Nucleus reset

Answer 6

Using light levels detected via the optic nerve

Question 7

How does the Suprachiasmatic Nucleus control sleepyness

Answer 7

By regulating the production and secretion of melatonin in the pineal gland via an interconnecting neural pathway

Question 8

What does exogenous mean

Answer 8

This refers to anything whose origins are outside the organism

Question 9

What are two examples of exogenous zeitgebers

Answer 9

Light and Social Cues

Question 10

How does light effects biological rhythms

Answer 10

Receptors in the SCN are sensitive to changes in light levels and use this information to synchronise the activity of the body’s organs and glands

Question 11

How do retinal cells help reset the biological clock

Answer 11

A small number of retinal cells contain melanopsin, a protein sentsitive to natural light, which carry signals to the SCN to reset the daily body cycle

Question 12

How do social cues effect biological rhythms

Answer 12

Social cues such as mealtimes and social activities may also have a role. Aschoff et al showed that individuals are able to compensate for the absence of zeitgebers by responding to social zeitgebers instead.

Question 13

What did one study on jet lag find

Answer 13

That the circadian rhythms of air travelers adjusted more quickly if they went outside more at their destination, and this was theorised to be because they were exposed to the social cues of the new time zone, however this can be better explained by light

Question 14

How do the circadian rhythms of blind people remain the same as non-blind people

Answer 14

They are reset by social cues, however this could be that their sleep-wake cycle is still influenced by light, as connections still exist between the eye and the SCN that do not involve those parts of the visual system on which the perception of light depends

Question 15

What study emphasised the importance of the SCN

Answer 15

Morgan’s study on hamsters, where he bred a strain of hamsters so they had abnormal circadian rhythms of 20 hours rather than 24 hours. SCN neurons from these hamsters were then transplanted into the brains of normal hamsters, and these normal hamsters displayed the same abnormal circadian rhythm of 20 hours. The opposite also applied when the SCN of normal hamsters was implanted in the brains of abnormal hamsters.

Question 16

Who did mad science shit on the brains of hamsters to prove points about the SCN

Answer 16

Morgan, who implanted the SCN of hamsters into other hamsters

Question 17

Discuss research into the effects of artificial light in adolescents

Answer 17

Touitou et al argued that exposure to artificial light at night results in disruptions of circadian rhythms, with his research showing that teenagers exposed to electronic media at night (particularly blue light LED) had suppression of melotonin secretion and circadian disruption. As a result, adolescent sleep becomes irregular. In the long run this is detremental to health.

Question 18

What is support for the role of light in the sleep wake cycle from blind people

Answer 18

A study of blind people showed the importance of light in setting circadian rhythms. Some blind people are able to reliably entrain their circadian rhythm in response to light despite a total lack in image forming visual perception. Skene and Arendt estimate that the vast majority of blind subjects who still have some light perception have normally entrained circadian rhythms. This suggests that the pathway from the retinal cells containing melanopsin to the SCN is still intact. As further evidence of this pathway’s importance in setting the biological clock, people without light perception show abnormal circadian entrainment

Question 19

What is the role of articifical light as a exogenous zeitgeber (Blue light vs Warm Light)

Answer 19

Vetter et al demonstrated the importance of light in the regulation of the sleep-wake and activity-rest pattern of two groups of volunteer participants over a five week study period. One group remained in normal ‘warm’ artificial light over the five weeks while the other group experineced artificial ‘blue-enriched’ light that had a spectral composition close to daylight. They found that participants working under ‘warm’ light synced their circadian rhythms each day with the natural light of dawn. Over the course of the study, sunrise advanced by 42 mins, but participants exposed to blue-enriched light did not show the same 42 minuite adjustement and instead synchronised their rhythms in office hours. The results confirm that light is the dominant zeitgeber for the SCN and that it’s effectivness depends on spectral compostion

Question 20

Who demonstrated the importance of light in sleep wake cycle using blue light

Answer 20

Vetter et al

Question 21

Who estimated the amount of blind people with normal circadian rhythms

Answer 21

Skene and Arendt estimate that the vast majority of blind subjects who still have some light perception have normally entrained circadian rhythms.

Question 22

Who is worried about teenagers being on their phones at night

Answer 22

Touitou