6.7: Endogenous pacemakers and the sleep/wake cycle

Question 1

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks)

Answer 1

Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms

Question 2

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.

Answer 2

The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain

Question 3

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.

Answer 3

It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle

Question 4

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle.

Answer 4

Nerve fibres connected to the eye cross in an area called the optic chiasm

Question 5

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle.
Nerve fibres connected to the eye cross in an area called the optic chiasm.

Answer 5

The suprachiasmatic nucleus (SCN) receives information about light directly from the optic chiasm and this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep

Question 6

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle.
Nerve fibres connected to the eye cross in an area called the optic chiasm.
The suprachiasmatic nucleus (SCN) receives information about light directly from the optic chiasm and this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.

Answer 6

The SCN passes the information on day length and light that it receives to the pineal gland, which is a pea-like structure in the brain just behind the hypothalamus

Question 7

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle.
Nerve fibres connected to the eye cross in an area called the optic chiasm.
The suprachiasmatic nucleus (SCN) receives information about light directly from the optic chiasm and this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
The SCN passes the information on day length and light that it receives to the pineal gland, which is a pea-like structure in the brain just behind the hypothalamus.

Answer 7

During the night, the pineal gland increases production of melatonin, which is a chemical that induces sleep and is inhibited during periods of wakefulness

Question 8

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle.
Nerve fibres connected to the eye cross in an area called the optic chiasm.
The suprachiasmatic nucleus (SCN) receives information about light directly from the optic chiasm and this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
The SCN passes the information on day length and light that it receives to the pineal gland, which is a pea-like structure in the brain just behind the hypothalamus.
During the night, the pineal gland increases production of melatonin, which is a chemical that induces sleep and is inhibited during periods of wakefulness.

First AO3 PEEL paragraph

Answer 8

The first AO3 PEEL paragraph is that there is research support for the role of the SCN in establishing and maintaining the circadian sleep/wake cycle

Question 9

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle.
Nerve fibres connected to the eye cross in an area called the optic chiasm.
The suprachiasmatic nucleus (SCN) receives information about light directly from the optic chiasm and this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
The SCN passes the information on day length and light that it receives to the pineal gland, which is a pea-like structure in the brain just behind the hypothalamus.
During the night, the pineal gland increases production of melatonin, which is a chemical that induces sleep and is inhibited during periods of wakefulness.

The first AO3 PEEL paragraph is that there is research support for the role of the SCN in establishing and maintaining the circadian sleep/wake cycle.
Example

Answer 9

For example, 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 and the sleep/wake cycle of the chipmunks disappeared

Question 10

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle.
Nerve fibres connected to the eye cross in an area called the optic chiasm.
The suprachiasmatic nucleus (SCN) receives information about light directly from the optic chiasm and this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
The SCN passes the information on day length and light that it receives to the pineal gland, which is a pea-like structure in the brain just behind the hypothalamus.
During the night, the pineal gland increases production of melatonin, which is a chemical that induces sleep and is inhibited during periods of wakefulness.

The first AO3 PEEL paragraph is that there is research support for the role of the SCN in establishing and maintaining the circadian sleep/wake cycle.
For example, 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 and the sleep/wake cycle of the chipmunks disappeared.

Answer 10

Further support comes from Ralph et al. (1990), who 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 11

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle.
Nerve fibres connected to the eye cross in an area called the optic chiasm.
The suprachiasmatic nucleus (SCN) receives information about light directly from the optic chiasm and this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
The SCN passes the information on day length and light that it receives to the pineal gland, which is a pea-like structure in the brain just behind the hypothalamus.
During the night, the pineal gland increases production of melatonin, which is a chemical that induces sleep and is inhibited during periods of wakefulness.

The first AO3 PEEL paragraph is that there is research support for the role of the SCN in establishing and maintaining the circadian sleep/wake cycle.
For example, 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 and the sleep/wake cycle of the chipmunks disappeared.
Further support comes from Ralph et al. (1990), who 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.

Answer 11

There is therefore strong research evidence for the effect of endogenous pacemakers on the sleep/wake cycle

Question 12

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle.
Nerve fibres connected to the eye cross in an area called the optic chiasm.
The suprachiasmatic nucleus (SCN) receives information about light directly from the optic chiasm and this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
The SCN passes the information on day length and light that it receives to the pineal gland, which is a pea-like structure in the brain just behind the hypothalamus.
During the night, the pineal gland increases production of melatonin, which is a chemical that induces sleep and is inhibited during periods of wakefulness.

The first AO3 PEEL paragraph is that there is research support for the role of the SCN in establishing and maintaining the circadian sleep/wake cycle.
For example, 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 and the sleep/wake cycle of the chipmunks disappeared.
Further support comes from Ralph et al. (1990), who 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.
There is therefore strong research evidence for the effect of endogenous pacemakers on the sleep/wake cycle.

Second AO3 PEEL paragraph

Answer 12

The second AO3 PEEL paragraph is that However, the research was based on animals and the anatomy of a chipmunk or a hamster is very different to that of humans so such findings may not have external validity across to human generalisation

Question 13

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle.
Nerve fibres connected to the eye cross in an area called the optic chiasm.
The suprachiasmatic nucleus (SCN) receives information about light directly from the optic chiasm and this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
The SCN passes the information on day length and light that it receives to the pineal gland, which is a pea-like structure in the brain just behind the hypothalamus.
During the night, the pineal gland increases production of melatonin, which is a chemical that induces sleep and is inhibited during periods of wakefulness.

The first AO3 PEEL paragraph is that there is research support for the role of the SCN in establishing and maintaining the circadian sleep/wake cycle.
For example, 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 and the sleep/wake cycle of the chipmunks disappeared.
Further support comes from Ralph et al. (1990), who 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.
There is therefore strong research evidence for the effect of endogenous pacemakers on the sleep/wake cycle.

The second AO3 PEEL paragraph is that However, the research was based on animals and the anatomy of a chipmunk or a hamster is very different to that of humans so such findings may not have external validity across to human generalisation.

Answer 13

A more disturbing issue however, particularly in relation to DeCoursey et al.’s study, concerns the ethics involved in such research

Question 14

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle.
Nerve fibres connected to the eye cross in an area called the optic chiasm.
The suprachiasmatic nucleus (SCN) receives information about light directly from the optic chiasm and this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
The SCN passes the information on day length and light that it receives to the pineal gland, which is a pea-like structure in the brain just behind the hypothalamus.
During the night, the pineal gland increases production of melatonin, which is a chemical that induces sleep and is inhibited during periods of wakefulness.

The first AO3 PEEL paragraph is that there is research support for the role of the SCN in establishing and maintaining the circadian sleep/wake cycle.
For example, 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 and the sleep/wake cycle of the chipmunks disappeared.
Further support comes from Ralph et al. (1990), who 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.
There is therefore strong research evidence for the effect of endogenous pacemakers on the sleep/wake cycle.

The second AO3 PEEL paragraph is that However, the research was based on animals and the anatomy of a chipmunk or a hamster is very different to that of humans so such findings may not have external validity across to human generalisation.
A more disturbing issue however, particularly in relation to DeCoursey et al.’s study, concerns the ethics involved in such research.

Answer 14

The chipmunks were exposed to considerable harm, and subsequent risk, when they were returned to their natural habitat

Question 15

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle.
Nerve fibres connected to the eye cross in an area called the optic chiasm.
The suprachiasmatic nucleus (SCN) receives information about light directly from the optic chiasm and this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
The SCN passes the information on day length and light that it receives to the pineal gland, which is a pea-like structure in the brain just behind the hypothalamus.
During the night, the pineal gland increases production of melatonin, which is a chemical that induces sleep and is inhibited during periods of wakefulness.

The first AO3 PEEL paragraph is that there is research support for the role of the SCN in establishing and maintaining the circadian sleep/wake cycle.
For example, 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 and the sleep/wake cycle of the chipmunks disappeared.
Further support comes from Ralph et al. (1990), who 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.
There is therefore strong research evidence for the effect of endogenous pacemakers on the sleep/wake cycle.

The second AO3 PEEL paragraph is that However, the research was based on animals and the anatomy of a chipmunk or a hamster is very different to that of humans so such findings may not have external validity across to human generalisation.
A more disturbing issue however, particularly in relation to DeCoursey et al.’s study, concerns the ethics involved in such research.
The chipmunks were exposed to considerable harm, and subsequent risk, when they were returned to their natural habitat.

Answer 15

By the end of the study, a significant proportion of them had been killed by predators (presumably because they were awake and vulnerable to attack when they should have been asleep) and it is argued that this was undoubtedly a direct consequence of the research

Question 16

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle.
Nerve fibres connected to the eye cross in an area called the optic chiasm.
The suprachiasmatic nucleus (SCN) receives information about light directly from the optic chiasm and this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
The SCN passes the information on day length and light that it receives to the pineal gland, which is a pea-like structure in the brain just behind the hypothalamus.
During the night, the pineal gland increases production of melatonin, which is a chemical that induces sleep and is inhibited during periods of wakefulness.

The first AO3 PEEL paragraph is that there is research support for the role of the SCN in establishing and maintaining the circadian sleep/wake cycle.
For example, 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 and the sleep/wake cycle of the chipmunks disappeared.
Further support comes from Ralph et al. (1990), who 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.
There is therefore strong research evidence for the effect of endogenous pacemakers on the sleep/wake cycle.

The second AO3 PEEL paragraph is that However, the research was based on animals and the anatomy of a chipmunk or a hamster is very different to that of humans so such findings may not have external validity across to human generalisation.
A more disturbing issue however, particularly in relation to DeCoursey et al.’s study, concerns the ethics involved in such research.
The chipmunks were exposed to considerable harm, and subsequent risk, when they were returned to their natural habitat.
By the end of the study, a significant proportion of them had been killed by predators (presumably because they were awake and vulnerable to attack when they should have been asleep) and it is argued that this was undoubtedly a direct consequence of the research.

Answer 16

Even in Ralph et al.’s study, the hamsters were left permanently damaged

Question 17

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle.
Nerve fibres connected to the eye cross in an area called the optic chiasm.
The suprachiasmatic nucleus (SCN) receives information about light directly from the optic chiasm and this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
The SCN passes the information on day length and light that it receives to the pineal gland, which is a pea-like structure in the brain just behind the hypothalamus.
During the night, the pineal gland increases production of melatonin, which is a chemical that induces sleep and is inhibited during periods of wakefulness.

The first AO3 PEEL paragraph is that there is research support for the role of the SCN in establishing and maintaining the circadian sleep/wake cycle.
For example, 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 and the sleep/wake cycle of the chipmunks disappeared.
Further support comes from Ralph et al. (1990), who 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.
There is therefore strong research evidence for the effect of endogenous pacemakers on the sleep/wake cycle.

The second AO3 PEEL paragraph is that However, the research was based on animals and the anatomy of a chipmunk or a hamster is very different to that of humans so such findings may not have external validity across to human generalisation.
A more disturbing issue however, particularly in relation to DeCoursey et al.’s study, concerns the ethics involved in such research.
The chipmunks were exposed to considerable harm, and subsequent risk, when they were returned to their natural habitat.
By the end of the study, a significant proportion of them had been killed by predators (presumably because they were awake and vulnerable to attack when they should have been asleep) and it is argued that this was undoubtedly a direct consequence of the research.
Even in Ralph et al.’s study, the hamsters were left permanently damaged.
Nevertheless,

Answer 17

Nevertheless, animal research has proved invaluable in enhancing knowledge in relation to endogenous pacemakers and the sleep/wake cycle, because it allows research to be conducted that could not have been done on humans and the SCN is the same in all mammalian species

Question 18

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle.
Nerve fibres connected to the eye cross in an area called the optic chiasm.
The suprachiasmatic nucleus (SCN) receives information about light directly from the optic chiasm and this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
The SCN passes the information on day length and light that it receives to the pineal gland, which is a pea-like structure in the brain just behind the hypothalamus.
During the night, the pineal gland increases production of melatonin, which is a chemical that induces sleep and is inhibited during periods of wakefulness.

The first AO3 PEEL paragraph is that there is research support for the role of the SCN in establishing and maintaining the circadian sleep/wake cycle.
For example, 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 and the sleep/wake cycle of the chipmunks disappeared.
Further support comes from Ralph et al. (1990), who 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.
There is therefore strong research evidence for the effect of endogenous pacemakers on the sleep/wake cycle.

The second AO3 PEEL paragraph is that However, the research was based on animals and the anatomy of a chipmunk or a hamster is very different to that of humans so such findings may not have external validity across to human generalisation.
A more disturbing issue however, particularly in relation to DeCoursey et al.’s study, concerns the ethics involved in such research.
The chipmunks were exposed to considerable harm, and subsequent risk, when they were returned to their natural habitat.
By the end of the study, a significant proportion of them had been killed by predators (presumably because they were awake and vulnerable to attack when they should have been asleep) and it is argued that this was undoubtedly a direct consequence of the research.
Even in Ralph et al.’s study, the hamsters were left permanently damaged.
Nevertheless, animal research has proved invaluable in enhancing knowledge in relation to endogenous pacemakers and the sleep/wake cycle, because it allows research to be conducted that could not have been done on humans and the SCN is the same in all mammalian species.
Therefore,

Answer 18

Therefore, what we learn from such research justifies the adverse procedures involved

Question 19

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle.
Nerve fibres connected to the eye cross in an area called the optic chiasm.
The suprachiasmatic nucleus (SCN) receives information about light directly from the optic chiasm and this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
The SCN passes the information on day length and light that it receives to the pineal gland, which is a pea-like structure in the brain just behind the hypothalamus.
During the night, the pineal gland increases production of melatonin, which is a chemical that induces sleep and is inhibited during periods of wakefulness.

The first AO3 PEEL paragraph is that there is research support for the role of the SCN in establishing and maintaining the circadian sleep/wake cycle.
For example, 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 and the sleep/wake cycle of the chipmunks disappeared.
Further support comes from Ralph et al. (1990), who 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.
There is therefore strong research evidence for the effect of endogenous pacemakers on the sleep/wake cycle.

The second AO3 PEEL paragraph is that However, the research was based on animals and the anatomy of a chipmunk or a hamster is very different to that of humans so such findings may not have external validity across to human generalisation.
A more disturbing issue however, particularly in relation to DeCoursey et al.’s study, concerns the ethics involved in such research.
The chipmunks were exposed to considerable harm, and subsequent risk, when they were returned to their natural habitat.
By the end of the study, a significant proportion of them had been killed by predators (presumably because they were awake and vulnerable to attack when they should have been asleep) and it is argued that this was undoubtedly a direct consequence of the research.
Even in Ralph et al.’s study, the hamsters were left permanently damaged.
Nevertheless, animal research has proved invaluable in enhancing knowledge in relation to endogenous pacemakers and the sleep/wake cycle, because it allows research to be conducted that could not have been done on humans and the SCN is the same in all mammalian species.
Therefore, what we learn from such research justifies the adverse procedures involved.

Third AO3 PEEL paragraph

Answer 19

The third AO3 PEEL paragraph is that research has revealed there are numerous circadian rhythms called peripheral oscillators in many organs and cells of the body, such as the adrenal gland, oesophagus, lungs, liver and skin

Question 20

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle.
Nerve fibres connected to the eye cross in an area called the optic chiasm.
The suprachiasmatic nucleus (SCN) receives information about light directly from the optic chiasm and this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
The SCN passes the information on day length and light that it receives to the pineal gland, which is a pea-like structure in the brain just behind the hypothalamus.
During the night, the pineal gland increases production of melatonin, which is a chemical that induces sleep and is inhibited during periods of wakefulness.

The first AO3 PEEL paragraph is that there is research support for the role of the SCN in establishing and maintaining the circadian sleep/wake cycle.
For example, 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 and the sleep/wake cycle of the chipmunks disappeared.
Further support comes from Ralph et al. (1990), who 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.
There is therefore strong research evidence for the effect of endogenous pacemakers on the sleep/wake cycle.

The second AO3 PEEL paragraph is that However, the research was based on animals and the anatomy of a chipmunk or a hamster is very different to that of humans so such findings may not have external validity across to human generalisation.
A more disturbing issue however, particularly in relation to DeCoursey et al.’s study, concerns the ethics involved in such research.
The chipmunks were exposed to considerable harm, and subsequent risk, when they were returned to their natural habitat.
By the end of the study, a significant proportion of them had been killed by predators (presumably because they were awake and vulnerable to attack when they should have been asleep) and it is argued that this was undoubtedly a direct consequence of the research.
Even in Ralph et al.’s study, the hamsters were left permanently damaged.
Nevertheless, animal research has proved invaluable in enhancing knowledge in relation to endogenous pacemakers and the sleep/wake cycle, because it allows research to be conducted that could not have been done on humans and the SCN is the same in all mammalian species.
Therefore, what we learn from such research justifies the adverse procedures involved.

The third AO3 PEEL paragraph is that research has revealed there are numerous circadian rhythms called peripheral oscillators in many organs and cells of the body, such as the adrenal gland, oesophagus, lungs, liver and skin.

Answer 20

Although these peripheral clocks are highly influenced by the actions of the SCN, they can act independently and there is research support for this

Question 21

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle.
Nerve fibres connected to the eye cross in an area called the optic chiasm.
The suprachiasmatic nucleus (SCN) receives information about light directly from the optic chiasm and this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
The SCN passes the information on day length and light that it receives to the pineal gland, which is a pea-like structure in the brain just behind the hypothalamus.
During the night, the pineal gland increases production of melatonin, which is a chemical that induces sleep and is inhibited during periods of wakefulness.

The first AO3 PEEL paragraph is that there is research support for the role of the SCN in establishing and maintaining the circadian sleep/wake cycle.
For example, 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 and the sleep/wake cycle of the chipmunks disappeared.
Further support comes from Ralph et al. (1990), who 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.
There is therefore strong research evidence for the effect of endogenous pacemakers on the sleep/wake cycle.

The second AO3 PEEL paragraph is that However, the research was based on animals and the anatomy of a chipmunk or a hamster is very different to that of humans so such findings may not have external validity across to human generalisation.
A more disturbing issue however, particularly in relation to DeCoursey et al.’s study, concerns the ethics involved in such research.
The chipmunks were exposed to considerable harm, and subsequent risk, when they were returned to their natural habitat.
By the end of the study, a significant proportion of them had been killed by predators (presumably because they were awake and vulnerable to attack when they should have been asleep) and it is argued that this was undoubtedly a direct consequence of the research.
Even in Ralph et al.’s study, the hamsters were left permanently damaged.
Nevertheless, animal research has proved invaluable in enhancing knowledge in relation to endogenous pacemakers and the sleep/wake cycle, because it allows research to be conducted that could not have been done on humans and the SCN is the same in all mammalian species.
Therefore, what we learn from such research justifies the adverse procedures involved.

The third AO3 PEEL paragraph is that research has revealed there are numerous circadian rhythms called peripheral oscillators in many organs and cells of the body, such as the adrenal gland, oesophagus, lungs, liver and skin.
Although these peripheral clocks are highly influenced by the actions of the SCN, they can act independently and there is research support for this.
Example

Answer 21

For example, Damiola et al. demonstrated how changing feeding patterns in mice could alter the circadian rhythms of cells in the liver by up to 12 hours, whilst leaving the rhythm of the SCN unaffected

Question 22

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle.
Nerve fibres connected to the eye cross in an area called the optic chiasm.
The suprachiasmatic nucleus (SCN) receives information about light directly from the optic chiasm and this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
The SCN passes the information on day length and light that it receives to the pineal gland, which is a pea-like structure in the brain just behind the hypothalamus.
During the night, the pineal gland increases production of melatonin, which is a chemical that induces sleep and is inhibited during periods of wakefulness.

The first AO3 PEEL paragraph is that there is research support for the role of the SCN in establishing and maintaining the circadian sleep/wake cycle.
For example, 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 and the sleep/wake cycle of the chipmunks disappeared.
Further support comes from Ralph et al. (1990), who 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.
There is therefore strong research evidence for the effect of endogenous pacemakers on the sleep/wake cycle.

The second AO3 PEEL paragraph is that However, the research was based on animals and the anatomy of a chipmunk or a hamster is very different to that of humans so such findings may not have external validity across to human generalisation.
A more disturbing issue however, particularly in relation to DeCoursey et al.’s study, concerns the ethics involved in such research.
The chipmunks were exposed to considerable harm, and subsequent risk, when they were returned to their natural habitat.
By the end of the study, a significant proportion of them had been killed by predators (presumably because they were awake and vulnerable to attack when they should have been asleep) and it is argued that this was undoubtedly a direct consequence of the research.
Even in Ralph et al.’s study, the hamsters were left permanently damaged.
Nevertheless, animal research has proved invaluable in enhancing knowledge in relation to endogenous pacemakers and the sleep/wake cycle, because it allows research to be conducted that could not have been done on humans and the SCN is the same in all mammalian species.
Therefore, what we learn from such research justifies the adverse procedures involved.

The third AO3 PEEL paragraph is that research has revealed there are numerous circadian rhythms called peripheral oscillators in many organs and cells of the body, such as the adrenal gland, oesophagus, lungs, liver and skin.
Although these peripheral clocks are highly influenced by the actions of the SCN, they can act independently and there is research support for this.
For example, Damiola et al. demonstrated how changing feeding patterns in mice could alter the circadian rhythms of cells in the liver by up to 12 hours, whilst leaving the rhythm of the SCN unaffected.
What does this suggest?

Answer 22

This suggests that there may be many other complex influences on the sleep/wake cycle, aside from the master clock (the SCN), such as light or social cues and there is evidence for this from Campbell and Murphy, who revealed that the SCN may not be the main endogenous pacemaker through altering circadian rhythms by shining light on the backs of participants’ knees, which shifted their rhythms

Question 23

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle.
Nerve fibres connected to the eye cross in an area called the optic chiasm.
The suprachiasmatic nucleus (SCN) receives information about light directly from the optic chiasm and this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
The SCN passes the information on day length and light that it receives to the pineal gland, which is a pea-like structure in the brain just behind the hypothalamus.
During the night, the pineal gland increases production of melatonin, which is a chemical that induces sleep and is inhibited during periods of wakefulness.

The first AO3 PEEL paragraph is that there is research support for the role of the SCN in establishing and maintaining the circadian sleep/wake cycle.
For example, 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 and the sleep/wake cycle of the chipmunks disappeared.
Further support comes from Ralph et al. (1990), who 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.
There is therefore strong research evidence for the effect of endogenous pacemakers on the sleep/wake cycle.

The second AO3 PEEL paragraph is that However, the research was based on animals and the anatomy of a chipmunk or a hamster is very different to that of humans so such findings may not have external validity across to human generalisation.
A more disturbing issue however, particularly in relation to DeCoursey et al.’s study, concerns the ethics involved in such research.
The chipmunks were exposed to considerable harm, and subsequent risk, when they were returned to their natural habitat.
By the end of the study, a significant proportion of them had been killed by predators (presumably because they were awake and vulnerable to attack when they should have been asleep) and it is argued that this was undoubtedly a direct consequence of the research.
Even in Ralph et al.’s study, the hamsters were left permanently damaged.
Nevertheless, animal research has proved invaluable in enhancing knowledge in relation to endogenous pacemakers and the sleep/wake cycle, because it allows research to be conducted that could not have been done on humans and the SCN is the same in all mammalian species.
Therefore, what we learn from such research justifies the adverse procedures involved.

The third AO3 PEEL paragraph is that research has revealed there are numerous circadian rhythms called peripheral oscillators in many organs and cells of the body, such as the adrenal gland, oesophagus, lungs, liver and skin.
Although these peripheral clocks are highly influenced by the actions of the SCN, they can act independently and there is research support for this.
For example, Damiola et al. demonstrated how changing feeding patterns in mice could alter the circadian rhythms of cells in the liver by up to 12 hours, whilst leaving the rhythm of the SCN unaffected.
This suggests that there may be many other complex influences on the sleep/wake cycle, aside from the master clock (the SCN), such as light or social cues and there is evidence for this from Campbell and Murphy, who revealed that the SCN may not be the main endogenous pacemaker through altering circadian rhythms by shining light on the backs of participants’ knees, which shifted their rhythms.

Answer 23

It may be that blood is the messenger that carries signals (light signals) across the body, from the skin to the brain, but this highlights that the SCN is not the main endogenous pacemaker as we assumed

Question 24

Discuss the effect of endogenous pacemakers on the sleep/wake cycle (16 marks).
Endogenous pacemakers are internal body clocks that regulate many of our biological rhythms.
The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
It is one the primary endogenous pacemakers in mammalian species (including humans) and is influential in maintaining circadian rhythms such as the sleep/wake cycle.
Nerve fibres connected to the eye cross in an area called the optic chiasm.
The suprachiasmatic nucleus (SCN) receives information about light directly from the optic chiasm and this continues even when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
The SCN passes the information on day length and light that it receives to the pineal gland, which is a pea-like structure in the brain just behind the hypothalamus.
During the night, the pineal gland increases production of melatonin, which is a chemical that induces sleep and is inhibited during periods of wakefulness.

The first AO3 PEEL paragraph is that there is research support for the role of the SCN in establishing and maintaining the circadian sleep/wake cycle.
For example, 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 and the sleep/wake cycle of the chipmunks disappeared.
Further support comes from Ralph et al. (1990), who 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.
There is therefore strong research evidence for the effect of endogenous pacemakers on the sleep/wake cycle.

The second AO3 PEEL paragraph is that However, the research was based on animals and the anatomy of a chipmunk or a hamster is very different to that of humans so such findings may not have external validity across to human generalisation.
A more disturbing issue however, particularly in relation to DeCoursey et al.’s study, concerns the ethics involved in such research.
The chipmunks were exposed to considerable harm, and subsequent risk, when they were returned to their natural habitat.
By the end of the study, a significant proportion of them had been killed by predators (presumably because they were awake and vulnerable to attack when they should have been asleep) and it is argued that this was undoubtedly a direct consequence of the research.
Even in Ralph et al.’s study, the hamsters were left permanently damaged.
Nevertheless, animal research has proved invaluable in enhancing knowledge in relation to endogenous pacemakers and the sleep/wake cycle, because it allows research to be conducted that could not have been done on humans and the SCN is the same in all mammalian species.
Therefore, what we learn from such research justifies the adverse procedures involved.

The third AO3 PEEL paragraph is that research has revealed there are numerous circadian rhythms called peripheral oscillators in many organs and cells of the body, such as the adrenal gland, oesophagus, lungs, liver and skin.
Although these peripheral clocks are highly influenced by the actions of the SCN, they can act independently and there is research support for this.
For example, Damiola et al. demonstrated how changing feeding patterns in mice could alter the circadian rhythms of cells in the liver by up to 12 hours, whilst leaving the rhythm of the SCN unaffected.
This suggests that there may be many other complex influences on the sleep/wake cycle, aside from the master clock (the SCN), such as light or social cues and there is evidence for this from Campbell and Murphy, who revealed that the SCN may not be the main endogenous pacemaker through altering circadian rhythms by shining light on the backs of participants’ knees, which shifted their rhythms.
It may be that blood is the messenger that carries signals (light signals) across the body, from the skin to the brain, but this highlights that the SCN is not the main endogenous pacemaker as we assumed.

Answer 24

Simplifying such an explanation through light is reductionist, as evidently more complex mechanisms are at work which we are not fully understanding