Biopsychology: Biological Rhythms

Question 1

What are biological rhythms?

Answer 1

A biological rhythm is any change in a physiological activity that repeats periodically in a set pattern.

Question 2

Biological Rhythms: Three Main Types

Answer 2

infradian
circadian
ultradian

Question 3

Endogenous Pacemakers: What are they?

Answer 3

These are internal body clocks that influence the patterns of our biological rhythms. These may be genetic mechanisms.

The help maintain regular rhythms in absence of zeitgebers but they are not perfect and need zeitgebers to synchronise the rhythms to our individual behaviours.

Examples:
Pineal Gland
Suprachiasmatic Nucleus

Question 4

Endogenous Pacemakers: Sleep-Wake Cycle

Answer 4

Our internal body clock is found in the hypothalamus and is called the suprachiasmatic nucleus (SCN) – this synchronises our sleep-wake circadian rhythm.
The SCN receives light through the eyes (optic nerve). When light levels drop (at night), this information is received by the SCN causing it to fire impulses to the pineal gland which then secretes melatonin which causes sleepiness.
When light increases (daytime), melatonin levels decrease heavily making us more alert.
Without light as a zeitgeber, the process ‘free runs’ to an average 25hr cycle.

Question 5

Exogenous Zeitgebers: Siffre (2002)

Answer 5

A French cave explorer, Michel Siffre, spent 6 months in an underground cave in Texas in 1972, separated from natural light / dark cycles.

This allowed him to investigate what happens when the bodily sleep-wake cycle is allowed to ‘free run’ away from exogenous zeitgebers.
He was wired up so that various bodily functions could be recorded. He ate and slept whenever he wanted.

At first, his sleep-wake cycle was very erratic, but settled down to a fairly regular pattern of between 25 and 30 hours, that is slightly longer than the ‘normal’ 24-hour cycle. What was actually 179 days, felt like 151 to him.

Question 6

What are exogenous zeitgebers?

Answer 6

These are external stimuli which provide information about elapsed time and prompt changes in bodily activity and the patterns of our biological rhythms.

Question 7

Exogenous Zeitgebers: In Summary…

Answer 7

Endogenous pacemakers (EP) and exogenous zeitgebers (EZ) interact in the control and fine tuning of biological rhythms.

This is a classic example of how nature and nurture are both instrumental in shaping our daily (or monthly) behaviour.

Notably, a key factor in maintaining rhythmic behaviour are the mechanisms underlying the interaction between EP and EZ, namely light.

Question 8

The Significance of Light as an EZ

Answer 8

Light is an EZ but it has a big impact on EP’s - particularly the suprachiasmatic nucleus.

In the sleep-wake cycle, falling light levels alert the SCN to “tell” the pineal gland to increase the secretion of melatonin. The increase in melatonin in the bloodstream reduces brain activity and causes drowsiness.

As morning approaches, increasing levels alert the SCN to “tell” the pineal gland to reduce the secretion of melatonin. The reduction in melatonin in the bloodstream increases brain activity and alertness.