Lesson 10 - Circadian Rhythms

Question 1

What are Biological Rhythms?

Answer 1

Biological Rhythms are cyclical changes in physiological systems (no start and no end) which have evolved because the environments which organisms inhabit have cyclical changes (night/day) (summer/winter).

Question 2

What are three types of biological rhythms?

Answer 2

Circadian
Ultradian
Infradian

Question 3

What is a circadian rhythm? (2)

Answer 3

Circadian rhythms refers to a biological rhythm that lasts for 24 hours.
Circadian rhythms optimise an organism’s physiology and behaviour to best meet the varying demands of the day cycle and night cycle.

Question 4

What and where is the suprachiasmatic nuclei? (SCN)

Answer 4

The Suprachiasmatic Nuclei is a tiny cluster of nerve cells located in the hypothalamus.

Question 5

What is the function of the SCN?

Answer 5

The Suprachiasmatic nucleus is a pacemaker which regulates circadian rhythms.

Question 6

What is Photoentrainment?

Answer 6

The SCN must constantly be reset so that our bodies are in synchrony with the changing outside world. This is achieved through a process called photoentrainment which is where natural light is detected, setting the SCN to the correct time so that it can coordinate activity of circadian rhythms throughout the body.

Question 7

What is the sleep-wake cycle?

Answer 7

The sleep-wake cycle is the rhythm people have regarding when we need to sleep and wake up.

Question 8

When are our strongest sleep drives?

Answer 8

• 2:00am - 4:00am

- 1:00pm - 3:00pm

Question 9

Where is melatonin released from?

Answer 9

The pineal gland

Question 10

What does melatonin do?

Answer 10

Melatonin is at its peak when it is dark. Melatonin helps induce (cause) sleep by inhibiting neural mechanisms which are responsible for wakefulness. Light stops the production of melatonin which allows us to wake up.

Question 11

What controls sleep and wakefulness?

Answer 11

Sleep and wakefulness are under homeostatic control

Question 12

How does Homeostasis control sleep and wakefulness?

Answer 12

The Homeostatic system tends to make a person sleepier the longer they have been awake and the more energy used whilst awake.

Question 13

What is the difference between circadian rhythms and the Homeostatic System?

Answer 13

Circadian rhythms - keep us awake as long as there is daylight and send us to sleep when it is dark.
Homeostatic System - tends to send us asleep the longer that we have been awake regardless of daylight and darkness.

Question 14

What is an advantage of circadian rhythms?

Answer 14

+ There are practical examples of circadian rhythms for example, chronotherapeutics. The success of treatment depends on the time medication was taken because it is essential that the right concentration of the drug is released at the time of which the drug is most needed. For example, there is a higher risk of getting a heart attack in the early hours of the morning. Therefore, drugs have been developed that can be taken before an individual goes to sleep but are not released into the bloodstream until the vulnerable time of 6:00am.

Question 15

What are 4 weaknesses of Circadian Rhythms?

Answer 15

• When carrying out research on circadian rhythms, researchers did not isolate participants from artificial light because it was believed that only natural light affected circadian rhythms. However, this may not be true where Cziesler et al. (1999) was able too alter a participants circadian rhythm down to 22 hours and up to 28 hours by only using artificial light.
• Cziesler et al. (1999) discovered how there are individual differences in the LENGTH of participants’ circadian rhythms differing from 13 to 165 hours!)
• There is another individual difference in circadian rhythms regarding when they reach their peak. For example, ‘morning people’ prefer to rise early and go to bed early as ‘evening people’ prefer to rise late.
• Buhr et al. (2010) believes that temperature controls our body clock and not light. The SCN converts the information it receives about light levels into neural messages which set the body’s temperature. The fluctuations in temperature set the timing of the cells in the body.