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A-level Psychology > Bio - Endogenous pacemakers & exogenous zeitgebers > Flashcards

Bio - Endogenous pacemakers & exogenous zeitgebers Flashcards

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1
Q

Endogenous pacemakers

A

Mechanisms within the body that govern the internal, biological bodily rhythms.

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2
Q

Exogenous zeitgeber

A

An environment cue, such as light, that helps to regulate the biological clock in an organism.

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3
Q

What are endogenous pacemakers sometimes referred to as?

A

Biological clocks.

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4
Q

What does the term endogenous refer to?

A

Anything whose origins are within the organism.

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5
Q

What are endogenous pacemakers most probably the products of?

A

Inherited genetic mechanisms.

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6
Q

What do endogenous pacemakers allow us to do?

A

Keep pace with changing cycles in the environment.

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7
Q

What is the most important pacemaker in human beings?

A

The suprachiasmatic nucleus (SCN).

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8
Q

What is the suprachiasmatic nucleus (SCN)?

A

The main endogenous pacemaker - a tiny cluster of nerve cells, which lies in the hypothalamus.

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9
Q

Where is the SCN?

A

It lies in the hypothalamus.

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10
Q

What does the SCN play a role in?

A

Generating the body’s circadian rhythm.

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11
Q

What does the SCN act as?

A

The ‘master clock’.

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12
Q

Why is the SCN so powerful?

A

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

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13
Q

How does the SCN work as an endogenous pacemaker?

A

Neurons within the SCN spontaneously synchronise with each other, so that their target neurons in sites elsewhere in the body receive correctly time-coordinated signals.

These peripheral clocks can maintain a circadian rhythm, but not for very long, which is why they must be controlled by the SCN.

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14
Q

Why is it possible for the SCN to control peripheral clocks in the body which cannot maintain a circadian rhythm for very long?

A

Because the SCN has a built-in circadian rhythm, which only needs resetting when external light levels change.

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15
Q

How does the circadian rhythm built-in to the SCN reset itself?

A

The SCN receives information about light levels via the optic nerve. This happens even when our eyes are shut, because light penetrates the eyelids. If our biological clock is running slow (e.g. the sun rises earlier than on the previous day), then morning light automatically adjusts the clock, putting its rhythm in step with the world outside. The SCN also regulates the manufacture and secretion of melatonin in the pineal gland via an interconnecting neural pathway.

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16
Q

What effect does the SCN have on hormones in the body?

A

The SCN regulates the manufacture and secretion of melatonin in the pineal gland via an interconnecting neural pathway.

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17
Q

What evidence is there for the SCN?

A

Similar studies from Ralph et al., (1990) and Morgan (1995).

Morgan, 1995:

  • Bred a strain of hamsters so that they had abnormal circadian rhythms of 20h rather than 24h.
  • SCN neurons from these abnormal hamsters were then transplanted into the brains of normal hamsters.
  • These normal hamsters then displayed that same abnormal circadian rhythm of 20h, showing that the transplanted SCN had imposed its pattern onto the recipients’ brains.
  • Morgan then transplanted SCN neurons from normal hamsters into the brains of the abnomal hamsters.
  • Rather than maintaining their abnormal circadian rhythm, the recipient hamsters then changed to a circadian pattern of 24h.
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18
Q

Are endogenous pacemakers internal or external stimuli?

A

Internal stimuli.

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19
Q

Are exogenous zeitgebers internal or external stimuli?

A

External stimuli.

20
Q

What endogenous pacemakers do we have in the human body?

A

SCN and pineal gland.

21
Q

What does SCN stand for?

A

Suprachiasmatic nucleus.

22
Q

Explain the pineal gland an an EP

A

The SCN sends signals to the pineal gland, directing it to increase production and secretion of the hormone melatonin at night and to decrease it as light levels increase in the morning.

23
Q

What controls the activity of the pineal gland?

A

The SCN.

24
Q

What does melatonin do and how does it do this?

A

Induces sleep by inhibiting the brain mechanisms that promote wakefulness.

25
Q

What does the SCN work jointly with as EPs in the brain?

A

The pineal gland.

26
Q

What does the pineal gland work jointly with as EPs in the brain?

A

The SCN.

27
Q

What does the sensitivity of the pineal gland and the SCN to light, and the role of melatonin in controlling sleep and activity mean there is/happens?

A

Means that despite the endogenous nature of these clocks, their activity must be synchronised with the light-dark rhythm of the world outside.

28
Q

What is melatonin derived from?

A

Serotonin (they are both inhibitory neurotransmitters).

29
Q

What does the term exogenous refer to?

A

Anything whose origins are outside the organism.

30
Q

What does ‘zeitgeber’ mean?

A

‘Zeit’ = ‘timer giver’.

31
Q

What is the most important zeitgeber for most animals?

A

Light.

32
Q

What exogenous zeitgebers do we have in/for the human body?

A

Light and social cues.

33
Q

Explain light as an exogenous zeitgeber

A

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 24h cycle.

Rods and cone in the retina of the eye detect light to form visual images. However, there is a third type of light-detecting cell in the retina that gauges overall brightness to help reset the internal biological clock. A protein called melanopsin, which is sensitive to natural light, is critical in this system. A small number of retinal cells contain melanopsin and carry signals to the SCN to set the daily body cycle.

34
Q

How often does light reset the internal biological clock?

A

Each day, keeping it on a 24h cycle.

35
Q

What detects the EZ that is light when resetting the internal biological clock?

A

Rods and cone in the retina of the eye detect light to form visual images. However, there is a third type of light-detecting cell in the retina that gauges overall brightness to help reset the internal biological clock. A protein called melanopsin, which is sensitive to natural light, is critical in this system. A small number of retinal cells contain melanopsin and carry signals to the SCN to set the daily body cycle.

36
Q

Where is melanopsin found in the retina of the eye?

A

In a third photoreceptor cell (the other two are rods and cones) called intrinsically photoreceptive retinal ganglion cells (ipRGCs).

37
Q

What is melanopsin?

A

A non-visual opsin used to detect light intensity/type of light.

38
Q

How does the level of light detected by the ganglion cells melanopsin reach the SCN?

A

Through the optic nerve.

39
Q

What information does the SCN use to synchronise its neurons?

A

The level of light detected by the ganglion cells melanopsin.

40
Q

What are some social cues that act as EZs?

A

Meal times, TV programmes, radio programmes, behavioural routines (e.g. reading before bed), regular working patterns, social activities, clubs, and hobbies.

41
Q

What did Aschoff et al. (1971) show about EZs?

A

Showed that individuals are able to compensate for the absence of zeitgebers such as natural light by responding to social zeitgebers instead.

42
Q

Who showed that individuals are able to compensate for the absence of zeitgebers such as natural light by responding to social zeitgebers instead?

A

Aschoff et al. (1971).

43
Q

What supporting evidence is there for social cues as an EZ?

A

One of the earliest studies on jet lag (Klein and Wegmann, 1974) found that the circadian rhythms of air travelers adjusted more quickly if they went outside more at their destination. This was thought to be because they were exposed to the social cues of their new time zone, which acted as a zeitgeber.

44
Q

How does the study of blind people link to social cues acting as EZs?

A

The circadian rhythms of blind people were thought to be no different to sighted people as both groups were exposed to the same social cues.

45
Q

How is the sleep-wake cycle of most blind people still influenced by light during the day, even though they have no visual perception?

A

Because connections exist between the eye and the SCN that do not involve those parts of the visual system on which the perception of light depends.

A-level Psychology (55 decks)

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