Sleep-wake Cycles

Question 1

Neural mechanisms of circadian clocks

Answer 1

Area of brain: suprachiasmatic nuclei located in the hypothalamus
Lesions of the SCN abolish sleep patterns
SCN displays circadian cycles of metabolic activity

Question 2

What controls the clock?

Answer 2

Active gene in nucleus creates mRNA leaves and creates protein in the cytoplasm
Critical level of protein in cytoplasm, some enter the nucleus stopping the gene producing mRNA, stopping production of protein
Protein levels fall and gene starts up again

Question 3

Setting the clock

Answer 3

Not fixed
We get over jet lag
In rats, cutting optic tracts before optic chasm meant light dark cycle could not set circadian rhythm

Question 4

Pineal gland

Answer 4

Seasonal rhythms - pineal gland secretes melatonin
During long nights - a lot released and animals enter winter mood
Lesions disrupt seasonal rhythms (Ralph and Lehman, 1991)
In humans, production of melatonin increases at night but lesions do not disrupt sleep pattern
SCN also controls timing of release of melatonin

Question 5

Innate

Answer 5

Rats born and raised in unchanging light environment show 25 hour sleep-wake cycles (Ritcher, 1971)

Human sleep-wake cycle 25.3 hours - Wever (1979)