The Effect Of Endogenous Pacemakers On The Sleep Wake Cycle

Question 1

What are endogenous pacemakers?

Answer 1

Internal body clocks that regulate biological rhythms, such as the SCN regulating the sleep/wake cycle.

Question 2

Can endogenous pacemakers function without environmental cues?

Answer 2

Yes, but their rhythms will alter over time without cues, which is why entrainment (resetting by external cues) is essential.

Question 3

What is the SCN and where is it located?

Answer 3

The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells in the hypothalamus, above the optic chiasm, and it is the main endogenous pacemaker in humans.

Question 4

How does the SCN maintain the sleep/wake cycle?

Answer 4

It receives light information through the optic chiasm, even when the eyes are closed, and adjusts circadian rhythms accordingly.

Question 5

What role does the pineal gland play in the sleep/wake cycle?

Answer 5

The SCN signals the pineal gland to produce melatonin at night, which induces sleep by inhibiting brain mechanisms that promote wakefulness.

Question 6

What does DeCoursey et al. (2000) show about the SCN?

Answer 6

Chipmunks with destroyed SCNs lost their sleep/wake rhythms and many were killed by predators, showing the SCN’s vital role in survival and rhythm regulation.

Question 7

What did Ralph et al. (1990) find in their hamster study?

Answer 7

Transplanting mutant hamsters’ SCNs into normal ones caused the normal hamsters to adopt the mutants’ 20-hour rhythm, proving the SCN’s role in setting circadian cycles.

Question 8

What did Morgan (1995) demonstrate with SCN transplants?

Answer 8

Abnormal SCN neurons transplanted into normal hamsters caused the recipients to adopt a 20-hour rhythm, and vice versa—highlighting the SCN’s determinative role.