✓ Endogenous Pacemakers (AO1)

Question 1

What is the Suprachiasmatic Nucleus?

Answer 1

the SCN is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain

it is the main endogenous pacemaker

it is crucial in the circadian rhythms of the sleep/wake cycle

Question 2

What is the Optic Chiasm?
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How does the SCN relate to the Optic Chiasm?

Answer 2

nerve fibres connected to the eye cross in an area called the optic chiasm on their way to the visual cortex
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the SCN is just above the optic chiasm & receives information abt light from this structure, adjusting our biological clocks

Question 3

What is the Role of Melatonin?

Answer 3

• the SCN passes info on daylight that it receives to the pineal gland
• during the night, the pineal gland increases production of melatonin
• melatonin is a chemical that induces sleep & is inhibited when awake
• melatonin may be a causal factor in Seasonal Affective Disorder

Question 4

What are 2 Animal Studies that explore the SCN & sleep/wake cycle?

Answer 4

Decoursey et al
Ralph et al

Question 5

What was Decoursey et al’s study?

Answer 5

destroyed the SCN in 30 chipmunks who were then returned to their natural habitat & observed for 80 days

the sleep/wake cycle disappeared & many had been killed by predators
(because they were awake when they should have been asleep)

Question 6

What was Ralph et al’s study?

Answer 6

bred ‘mutant’ hamsters with 20 hour sleep/wake cycle

when SCN of mutant hamsters was transplanted into normal hamsters, the normal hamsters sleep/wake cycle changed to 20 hours