Endogenous Pacemakers and Exogenous Zeitgebers

Question 1

What are endogenous pacemakers?

Answer 1

Internal body clocks that influence biological rhythms.

Question 2

Give 1 example of an endogenous pacemaker.

Answer 2

The suprachiasmatic nucleus influences the sleep wake cycle.

Question 3

What are exogenous zeitgebers?

Answer 3

External factors that affect our biological rhythms.

Question 4

Give 1 example of an exogenous zeitgeber.

Answer 4

Light - influences sleep wake cycle.

Question 5

What is the suprachiasmatic nucleus?

Answer 5

A tiny bundle of nerve cells located in the hypothalamus in each hemisphere.

Question 6

Outline the suprachiasmatic nucleus’ role in the sleep wake cycle.

Answer 6

1. Receives info about light directly from optic chiasm even when eyes are closed.
2. Information allows biological clock to adjust to changing patterns of daylight.
3. Regulates melatonin production + secretion of pineal gland.
4. Increases melatonin at night and decreases levels when light increases: makes humans sleepy at night.

Question 7

What hormone does the pineal gland produce?

Answer 7

Melatonin

Question 8

Outline the role of exogenous zeitgebers in the sleep wake cycle.

Answer 8

1. Light is an external cue.
2. SCN receptors are sensitive to light.
3. Retinal cells carry melanopsin - this carries signals to the SCN to reset body clock.

Question 9

What is melanopsin?

Answer 9

A protein which is light sensitive.

Question 10

Give 2 strengths of endogenous pacemakers and exogenous zeitgebers.

Answer 10

1. External cues can help travellers avoid jet lag.
   Studies: when travellers are subject to bright exposure before flight, they adjust earlier to a new time zone.
   This shows, individuals’ circadian rhythms can be trained so they don’t feel as fatigued.
   Therefore, real life application in improving adjusting to new sleep wake cycles - this has implications in economy.
2. Research support.
   Ralph et al : mutant hamsters SCN in normal hamsters - adjusted to 20 hr cycle.
   Shows SCN play significant role in sleep wake cycle.
   Therefore, increased credibility surrounding SCN as a primary endogenous pacemaker that drives internal clock.

Question 11

Give one limitation of endogenous pacemakers and exogenous zeitgebers.

Answer 11

1. Biologically reductionist.
   Behaviourism: bodily rhythms are a result of learning behaviours such as social norms of sleeping at night.
   Shows EPM fail to acknowledge role of social interactions.
   Therefore, may be an incomplete explanation.