Biopsychology : Biological Rhythms

Question 1

Biological Rhythms

Answer 1

Biological rhythms are cyclical patterns within biological systems that have evolved in response to environmental influences, e.g. day and night. There are two key factors that govern biological rhythms: endogenous pacemakers (internal), the body’s biological clocks, and exogenous zeitgebers (external), which are changes in the environment

Question 2

Circadian

Answer 2

One biological rhythm is the 24-hour circadian rhythm (often known as the ‘body clock’), which is reset by levels of light. The word circadian is from the Latin ‘circa’ which means ‘about’, and ‘dian’, which means ‘day’.

Example: the sleep wake cycle and body temperature

Question 3

Infradian rhythm

Answer 3

Another important biological rhythm is the infradian rhythm. Infradian rhythms last longer than 24 hours and can be weekly, monthly or annually. A monthly infradian rhythm is the female menstrual cycle, which is regulated by hormones that either promote ovulation or stimulate the uterus for fertilisation.

Question 4

Ultradian

Answer 4

Ultradian rhythms last fewer than 24 hours and can be found in the pattern of human sleep. This cycle alternates between REM (rapid eye movement) and NREM (non-rapid movement) sleep and consists of five stages. The cycle starts at light sleep, progressing to deep sleep and then REM sleep, where brain waves speed up and dreaming occurs. This repeats itself about every 90 minutes throughout the night.

Question 5

Endogenous pacemakers

Answer 5

Endogenous pacemakers are internal mechanisms that govern biological rhythms, in particular the circadian sleep/wake cycle. Although endogenous pacemakers are internal biological clocks, they can be affected by the environment. The most important endogenous pacemaker is the suprachiasmatic nucleus which is closely linked to the pineal gland, both of which are influential in maintaining the circadian sleep-wake cycle.

Question 6

Exogenous zeitgebers ?

Answer 6

exogenous zeitgebers influence biological rhythms: these can be described as environmental events that are responsible for resetting the biological clock of an organism. They can include social cues such as meal times and social activities, but the most important zeitgeber is light, which is responsible for resetting the body clock each day, keeping it on a 24-hour cycle.

Question 7

What is the sleep wake cycle?

Answer 7

• It is a circadian rhythm
• The sleep-wake cycle is an example of a circadian rhythm, which dictates when humans and animals should be asleep and awake. Light provides the primary input to this system, acting as the external cue for sleeping or waking. Light is first detected by the eye, which then sends messages concerning the level of brightness to the suprachiasmatic nuclei (SCN).

-The SCN then uses this information to coordinate the activity of the entire circadian system. Sleeping and wakefulness are not determined by the circadian rhythm alone, but also by homoeostasis. When an individual has been awake for a long time, homeostasis tells the body that there is a need for sleep because of energy consumption. This homeostatic drive for sleep increases throughout the day, reaching its maximum in the late evening, when most people fall asleep.

Question 8

What is body temperature

Answer 8

• Another circadian rhythm
• Body temperature is another circadian rhythm. Human body temperature is at its lowest in the early hours of the morning (36oC at 4:30 am) and at its highest in the early evening (38oC at 6 pm). Sleep typically occurs when the core temperature starts to drop, and the body temperature starts to rise towards the end of a sleep cycle promoting feelings of alertness first thing in the morning.

Question 9

Evaluating Circadian Rhythms

Answer 9

• Research Support: Research has been conducted to investigate circadian rhythms and the effect of external cues like light on this system. Siffre (1975) found that the absence of external cues significantly altered his circadian rhythm: When he returned from an underground stay with no clocks or light, he believed the date to be a month earlier than it was. This suggests that his 24-hour sleep-wake cycle was increased by the lack of external cues, making him believe one day was longer than it was, and leading to his thinking that fewer days had passed.
• Individual differences

Question 10

What is The most important endogenous pacemaker

Answer 10

The most important endogenous pacemaker is the suprachiasmatic nucleus, which is closely linked to the pineal gland, both of which are influential in maintaining the circadian sleep/wake cycle.

Question 11

What is the suprachiasmatic nucleus (SCN)

Answer 11

The suprachiasmatic nucleus (SCN), which lies in the hypothalamus, is the main endogenous pacemaker (or master clock). It controls other biological rhythms, as it links to other areas of the brain responsible for sleep and arousal. The SCN also receives information about light levels (an exogenous zeitgeber) from the optic nerve, which sets the circadian rhythm so that it is in synchronisation with the outside world, e.g. day and night.

Question 12

What does the SNC do?

Answer 12

The SNC sends signals to the pineal gland, which leads to an increase in the production of melatonin at night, helping to induce sleep. The SCN and pineal glands work together as endogenous pacemakers; however, their activity is responsive to the external cue of light.

Question 13

Process of falling to sleep

Answer 13

• Low levels of light (retina)
• Melanospin carriers signals to SCN
• Axon pathway to pineal gland
• Melatonin
• Induced sleep

Question 14

How is the 24 hour daily body cycle set?

Answer 14

The SNC contains receptors that are sensitive to light and this external cue is used to synchronise the body’s internal organs and glands. Melanopsin, which is a protein in the eye, is sensitive to light and carries the signals to the SCN to set the 24-hour daily body cycle.

Question 15

Evaluation of Endogenous pacemakers & Exogenous Zeitgebers

Answer 15

• The importance of the SCN has been demonstrated in research. Morgan (1955) bred hamsters so that they had circadian rhythms of 20 hours rather than 24. SCN neurons from these abnormal hamsters were transplanted into the brains of normal hamsters, which subsequently displayed the same abnormal circadian rhythm of 20 hours, showing that the transplanted SCN had imposed its pattern onto the hamsters. This research demonstrates the significance of the SCN and how endogenous pacemakers are important for biological circadian rhythms.

However, this research is flawed because of its use of hamsters. Humans would respond very differently to manipulations of their biological rhythms, not only because we are different biologically, but also because of the vast differences between environmental contexts. This makes research carried out on other animals unable to explain the role of endogenous pacemakers in the biological processes of humans.

• There is further research support for the role of exogenous zeitgebers. When Siffre (see above) returned from an underground stay with no clocks or light, he believed the date to be a month earlier than it was. This suggests that his 24-hour sleep-wake cycle was increased by the lack of external cues, making him believe one day was longer than it was. This highlights the impact of external factors on bodily rhythms.

Question 16

Explain how the female menstrual cycle works? ( example of Infradian)

Answer 16

A monthly infradian rhythm is the female menstrual cycle, which is regulated by hormones that either promote ovulation or stimulate the uterus for fertilisation. Ovulation occurs roughly halfway through the cycle when oestrogen levels are at their highest, and usually lasts for 16-32 hours. After the ovulatory phase, progesterone levels increase in preparation for the possible implantation of an embryo in the uterus. It is also important to note that although the usual menstrual cycle is around 28 days, there is considerable variation, with some women experiencing a short cycle of 23 days and others experiencing longer cycles of up to 36 days.

Question 17

What is SAD ( second example of Infradian rhythm)

Answer 17

A second example of an infradian rhythm is related to the seasons. Research has found seasonal variation in mood, where some people become depressed in the winter, which is known as seasonal affective disorder (SAD). SAD is an infradian rhythm that is governed by a yearly cycle. Psychologists claim that melatonin, which is secreted by the pineal gland during the night, is partly responsible. The lack of light during the winter months results in a longer period of melatonin secretion, which has been linked to the depressive symptoms.

Question 18

Evaluation of Infradian rhythm

Answer 18

Research suggests that the menstrual cycle is, to some extent, governed by exogenous zeitgebers (external factors) Russell et al. (1980) found that female menstrual cycles became synchronised with other females through odour exposure. In one study, sweat samples from one group of women were rubbed onto the upper lip of another group. Despite the fact that the two groups were separate, their menstrual cycles synchronised. This suggests that the synchronisation of menstrual cycles can be affected by pheromones, which have an effect on people nearby rather than on the person producing them. These findings indicate that external factors must be taken into consideration when investigating infradian rhythms and that perhaps a more holistic approach should be taken, as opposed to a reductionist approach that considers only endogenous influences.

Evolutionary psychologists claim that the synchronised menstrual cycle provides an evolutionary advantage for groups of women, as the synchronisation of pregnancies means that childcare can be shared among multiple mothers who have children at the same time.

Question 19

What is a complete sleep cycle?( Ultradian rhythms)

Answer 19

A complete sleep cycle goes through the four stages of NREM sleep before entering REM (Stage 5) and then repeating. Research using EEG has highlighted distinct brain waves patterns during the different stages of sleep.

Stages 1 and 2 are ‘light sleep’ stages. During these stages brainwave patterns become slower and more rhythmic, starting with alpha waves progress to theta waves.

Stages 3 and 4 are ‘deep sleep’ or slow wave sleep stages, where it is difficult to wake someone up. This stage is associated with slower delta waves.

Finally, Stage 5 is REM (or dream) sleep. Here is the body is paralysed (to stop the person acting out their dream) and brain activity resembles that of an awake person.

On average, the entire cycle repeats every 90 minutes and a person can experience up to five full cycles in a night.

Question 20

Evaluation Ultradian rhythms

Answer 20

Individual Differences: The problem with studying sleep cycles is the differences observed in people, which make investigating patterns difficult. Tucker et al. (2007) found significant differences between participants in terms of the duration of each stage, particularly stages 3 and 4 (just before REM sleep). This demonstrates that there may be innate individual differences in ultradian rhythms, which means that it is worth focusing on these differences during investigations into sleep cycles.

In addition, this study was carried out in a controlled lab setting, which meant that the differences in the sleep patterns could not be attributed to situational factors, but only to biological differences between participants. While this study provide convincing support for the role of innate biological factors and ultradian rhythms, psychologists should examine other situational factors that may also play a role.

• When investigating sleep patterns, participants must be subjected to a specific level of control and be attached to monitors that measure such rhythms. This may be invasive for the participant, leading them to sleep in a way that does not represent their ordinary sleep cycle. This makes investigating ultradian rhythms, such as the sleep cycle, extremely difficult as their lack of ecological validity could lead to false conclusions being drawn.