Biological rhythms

Question 1

What is a biological rhythm?

Answer 1

Something repeated regularly. Living things are governed by a variety of rhythms controlled by internal (endogenous) mechanisms and external factors (exogenous)

Question 2

What are circadian rhythms?

Answer 2

Daily rhythms that last for about 24 hours

Examples:
-Sleep/wake cycle
-Body temperature
-Release of hormones

Question 3

What are ultradian rhythms?

Answer 3

A type of biological rhythm with a frequency of more than one cycle in 24 hours

Examples:
-Sleep cycles (90 mins each)

Question 4

What are infradian rhythms?

Answer 4

A type of biological rhythm with a frequency of less than one cycle in 24 hours

Examples:
-Menstrual cycles

Question 5

What are the two reasons for why the sleep/wake cycle is 24 hours?

Answer 5

1. It is governed by an internal body clock- endogenous pacemakers
2. It is influenced by external factors such as the light/dark cycle- exogenous zeitgebers

Question 6

What are endogenous pacemakers?

Answer 6

-Internal body clocks that determine when we sleep and wake up

-Does it work alone or does it need external cues?
-This has been investigated by removing people from normal dark/light cycle and normal cues to see what happens to their sleep/wake cycle

Question 7

What are exogenous zeitgebers?

Answer 7

-External cues that entrain the sleep/wake cycle

Examples:
-Light
-Social cues
-Meal times
-Clocks

Question 8

What did Michael Siffre do and find in his study?

Answer 8

Conducted a series of studies on himself, in which he was isolated in a cave for up to six months

He settled down into a 25 hour cycle, showing it is similar to our 24 hour cycle, showing there is an internal body clock, but not the exact same, so external factors contribute

Question 9

What did Aschoff and Wever do and find in their study?

Answer 9

Participants spent several weeks in WW2 bunkers

They settled down into a 25 hour cycle, showing it is similar to our 24 hour cycle, showing there is an internal body clock, but not the exact same, so external factors contribute

Question 10

What could explain these one hour differences?

Answer 10

The extra one hour is adaptive because it allows us to adapt to stay up later if we need to. It is built-in flexibility

Question 11

What is entrainment?

Answer 11

The process where external cues keep the body clock in line with the 24 hour clock

Example:
Light

Question 12

What is the free running body clock?

Answer 12

The body’s internal sleep/wake cycle without external cues. Is around 25 hours

Question 13

What is the pineal gland’s involvement in our internal body clock?

Answer 13

-The pineal gland is where melatonin is produced > the hormone associated with sleep
-Melatonin induces sleep by inhibiting the brain mechanisms that promote wakefulness
-In humans the pineal gland is controlled by the SCN

Question 14

What is the Suprachiasmatic nucleus’ (SCN) involvement in our internal body clock?

Answer 14

-Mammals have a SCN. This is a small group of cells in the hypothalamus
-A pathway connects the retina of each eye to the SCN, allowing the amount of light to influence the activity of SCN neurons
-The SCN regulates the production of melatonin in the pineal gland via a connecting pathway

Question 15

What did DeCoursey et al find as supporting evidence for the SCN?

Answer 15

-Destroyed the SCN in the brains of 30 chipmunks
-The sleep/wake cycle of the chipmunks had disappeared
-By the end of the study most had been eaten by predators
-This suggests they were asleep when they should have been awake
-Shows SCN is vital in regulating the sleep-wake cycle
-However humans have a better understanding of time so may not happen to the same extent

Question 16

What are exogenous zeitgebers?

Answer 16

-Includes things like light, social cues and clocks
-Research suggests that these exogenous factors are important in adjusting the endogenous pacemakers to be in synchrony with the 24 hour day/night cycle
-They allow flexibility that is needed with fluctuating light patterns and lifestyles

Question 17

What are exogenous zeitgeber’s relevance to the SCN?

Answer 17

-Light is the most important zeitgeber in humans
-Light can reset the SCN through the eyes
-Campbell and Murphy showed that shining a light on the back of the knee can shift circadian rhythms
-Shows cells throughout the body contains proteins that are sensitive to light

Question 18

What are the three practical applications of this as a strength of SCN?

Answer 18

Shift work- we can entrain the body clock (SCN) by exposure to light at night and make sure it is dark when trying to sleep during the day

Jet lag- we can adapt to local times for sleeping and eating (social cues) to entrain the body clock

Train babies to sleep- use social cues such as meal and bed times and light to entrain the body clock. You can take babies outside and expose them to light in the day and then dark at night

Question 19

What are individual differences as a limitation of SCN?

Answer 19

-Cycle length varies from 13 to 65

-Difference in timing of cycle onset:
*Research shows there are ‘larks’ and ‘owls’
*Neuroscientists suggest teenage circadian rhythms start 2 hours after adults