circadian rhythms, endogenous pacemakers and exogenous zeitgebers

Question 1

what are circadian rhythms?

Answer 1

• 24 hour biological rhythm
• reset by levels of light

Question 2

give an example of a circadian rhythm

Answer 2

the sleep wake cycle
- light is the primary input, the external cue for sleeping or waking
- the eye detects light, which sends messages regarding the brightness to the suprachiasmatic nuclei (SCN)
- the SCN uses this info to coordinate the activity of the entire circadian system
- sleep-wake cycle is also controlled by homeostasis (e.g. it may tell the body there’s a need for sleep due to energy consumption)

Question 3

give another example of a circadian rhythm

Answer 3

body temperature
- lowest in the early morning (36 at 4.30am)
- highest in early evening (38 at 6pm)
- sleep occurs when body temp drops, and body temp rises at the end of a sleep cycle promoting feelings of alertness in the morning

Question 4

give a strength of circadian rhythms
1/1

Answer 4

research supports the effect of external cues on circadian rhythms. siffre found when he returned from an underground stay with no clocks or light he believed it to be a month earlier than it was, suggesting his sleep-wake cycle was increased by a lack of external cues. supported by participants who lived in a bunker with only artificial light, their sleep-wake cycle increased to 25-27 hours. both suggest humans use light (exogenous zeitgebers) to regulate the sleep wake cycle

Question 5

give a limitation of circadian rhythms
1/2

Answer 5

duffy et al found morning people prefer to wake and go to bed early (10 pm-6 am) whereas night people prefer to wake and go to bed later (1 am-10 am). suggests there may be innate individual differences in circadian rhythms which should be focused on during investigations

Question 6

give a limitation of circadian rhythms
2/2

Answer 6

temp may be more important than light in determining circadian rhythms. buhr et al found temp fluctuations set the timings of body cells and caused tissues or organs to be active or inactive. it fluctuates on a 24-hour circadian rhythm and small changes can send powerful signals to our body clock. so several factors influence circadian rhythms and a holistic approach to research may be better

Question 7

what are endogenous pacemakers?

Answer 7

• internal mechanisms that govern biological rhythms
• they can be influenced by the environment, e.g. light is required to reset the sleep-wake cycle every 24 hours

Question 8

give an example of an endogenous pacemaker

Answer 8

• the suprachiasmatic nucleus, closely linked to the pineal gland, both help maintain the sleep-wake cycle
• the SCN controls other biological rhythms, as its linked to other brain areas responsible for sleep and arousal
• SCN also receives info about light from the optic nerve
• SCN sends signals to the pineal gland to increase melatonin production at night to induce sleep

Question 9

what are exogenous zeitgebers?

Answer 9

• environmental events that reset the biological clock of an organism
• they can be social cues like meal times and social activities

Question 10

what is the most important exogenous zeitgeber?

Answer 10

light
- the SCN has light-sensitive receptors which synchronise the body’s internal organs and glands
- melanopsin carries signals to the SCN to set the 24 hour cycle

Question 11

give a strength of endogenous pacemakers and exogenous zeitgebers
1/3

Answer 11

research demonstrates SCN importance. morgan bred hamsters so they had circadian rhythms of 20 hrs not 24, by implanting SCN neurons from abnormal hamsters into the brains of normal ones, so the transplanted SCN imposed its pattern onto the hamsters. shows significance of SCN and how endogenous pacemakers are important for circadian rhythms.

COUNTER = criticised for its use of hamsters. humans would respond differently as were different biologically and have different environmental contexts

Question 12

give a strength of endogenous pacemakers and exogenous zeitgebers
2/3

Answer 12

research supports the role of melanopsin. skene and aren’t said most blind people with some light perception have normal circadian rhythms, and those without have abnormal ones. shows the importance of exogenous zeitgebers as a bio mechanism and its impact on bio circadian rhythms

Question 13

give a strength of endogenous pacemakers and exogenous zeitgebers
3/3

Answer 13

research supports the role of exogenous zeitgebers. siffre stayed underground with no clocks or light and when he returned he thought it was a month earlier. his 24 hr sleep wake cycle was increased by the lack of external cues, showing the impact of external factors on bodily rhythms

Question 14

give a limitation of endogenous pacemakers and exogenous zeitgebers
1/1

Answer 14

could be biologically reductionist. e.g. an approach like the behaviourist may suggest bodily rhythms are influenced by other people and social norms. this research may be criticised for being reductionist as it only considers a single biological mechanism

Question 15

how can biological rhythms be disrupted

Answer 15

people who work night shifts often experience jet lag symptoms as their work schedule (exogenous zeitgeber) is at odds with their sleep wake cycle, which is governed by endogenous pacemakers

Question 16

name a consequence of working night shifts
1/3

Answer 16

sleep deprivation:
- have to sleep during the day and often have difficulty sleeping
- their bio clocks (endogenous pacemakers) don’t fully adjust

Question 17

name a consequence of working night shifts
2/3

Answer 17

heart disease:
- relationship between shift work and heart disease
- found people who work shift patters for over 15 years were more likely to develop heart disease

Question 18

name a consequence of working night shifts
3/3

Answer 18

social consequences:
- often at odds with hours worked by their family and friends, so find it hard to spend quality time with others