Endogenous pacemakers & Exogenous zeitgebers

Question 1

What are endogenous pacemakers?

Answer 1

Internal biological clocks that regulate biological rhythms, such as the circadian sleep-wake cycle

Question 2

Can endogenous pacemakers function without environmental cues?

Answer 2

Yes, but they rely on external cues like light to reset the cycle every 24 hours.

Question 3

What is the most important endogenous pacemaker

Answer 3

The suprachiasmatic nucleus (SCN), located in the hypothalamus.

Question 4

What does the SCN do?

Answer 4

It regulates biological rhythms by linking to brain areas controlling sleep and arousal and receiving light information from the optic nerve

Question 5

How does the SCN control melatonin production

Answer 5

The SCN sends signals to the pineal gland to increase melatonin production at night, inducing sleep

Question 6

What role does light play in endogenous pacemakers?

Answer 6

Light acts as an external cue (exogenous zeitgeber) that helps reset the SCN’s control over biological rhythms.

Question 7

What are exogenous zeitgebers?

Answer 7

External cues, like light and social activities, that help regulate biological rhythms by resetting internal clocks.

Question 8

What is the most important exogenous zeitgeber?

Answer 8

Light, as it resets the body clock daily, maintaining the 24-hour cycle.

Question 9

How does light reset the body’s biological clock?

Answer 9

• Light-sensitive receptors in the SCN detect light.
• Signals from melanopsin, a protein in the eye, help adjust the circadian rhythm.

Question 10

Can social cues act as zeitgebers?

Answer 10

Yes, mealtimes and social activities can help regulate biological rhythms, especially in the absence of natural light.

Question 11

What is melanopsin?

Answer 11

A light-sensitive protein in the eye that sends signals to the SCN to set the 24-hour body clock.

Question 12

Support for the mechanisms of the sleep/wake cycle

Answer 12

Studies of blind people

• Some blind individuals maintain a 24-hour sleep/wake cycle despite lacking light perception.
• Suggests the pathway from the optic nerve to the SCN is intact, reinforcing the SCN’s role in setting a 24-hour cycle.

Question 13

Using light exposure to avoid jet lag

Answer 13

Bright light exposure prior to east-west flights

Participants shifted their circadian rhythm by 2.1 hours.
Helped them feel sleepier two hours later and wake up two hours earlier, reducing jet lag.

Question 14

Challenging the role of exogenous zeitgebers

Answer 14

Miles et al. (1977)

• A blind man had a 24.9-hour sleep/wake cycle that couldn’t adjust despite social cues like meal times.
• Suggests social cues alone are insufficient without functioning endogenous mechanisms like the SCN.