12- endogenous pacemakers and exogenous zeitgebers

Question 1

what do the biological rhythms get rest every day by

Answer 1

• endogenous pacemakers (internal biological rhythms)

- exogenous zeitgebers (external cues/factors e.g. light)

Question 2

what is the most important endogenous pacemaker

Answer 2

the SCN

Question 3

what is the SCN and what does it do

Answer 3

• tiny cluster of nerve cells in the hypothalamus
• generates circadian rhythms
• acts as master clock and links brain regions that control sleep and arousal
• controls biological clocks throughout the body

Question 4

how does the SCN control cells in the body

Answer 4

• neurons in SCN synchronise so target neurone in tour body parts get time-coordinated signals
• these peripheral clocks can’t maintain a circadian rhythm for long so SCN controls them
• SCN only gets reset when external light levels change
• receives light info through the optic nerve
• if biological clock is slow, morning light shifts the clock

Question 5

how does the SCN regulate manufacture and secretion of melatonin

Answer 5

• regulates manufacture and secretion of melatonin in the pineal gland via the interconnecting neural pathway
• signal sent to the pineal gland to increase melatonin at night and decrease as light increases in the morning

Question 6

how does melatonin induce sleep

Answer 6

by inhibiting the brain mechanisms that promote wakefulness

Question 7

positive evaluation of endogenous pacemakers (1)

Answer 7

+ university student (Kate Aldcroft) studied for 25 days in a lab with no light access or other exogenous zeitgebers and at the end her core temperature rhythm was still at 24 hours

Question 8

negative evaluation of endogenous pacemakers (1)

Answer 8

• Kate Aldcroft’s sleep-wake cycle was extended to 30 hours and she could sleep as long as 16 hours so we do need external influences to maintain our circadian rhythms

Question 9

what are exogenous zeitgebers

Answer 9

environmental events that are responsible for maintaining the biological clock of an organism

Question 10

what is the most important exogenous zeitgeber for animals

Answer 10

light

Question 11

how does light affect the SCN

Answer 11

• receptors in the SCN are sensitive to changes in light levels during the day and use this information to synchronise the activity of the body’s organs and glands
• resets internal biological everyday to maintain 24h cycle

Question 12

what is melanopsin

Answer 12

protein in the retina which is sensitive to natural light

Question 13

what effect does travelling to different time zones and night shift have

Answer 13

• endogenous pacemakers try to impose their inbuilt rhythm of sleep (circadian rhythm), but this is now out of synchrony with the exogenous zeitgeber of light
• lead to disrupted sleep patterns, increased anxiety and decreased alertness and vigilance

Question 14

positive evaluation of exogenous zeitgebers (3)

Answer 14

• majority of blind subjects who have some light perception have normal circadian rhythms whereas those without have abnormal circadian rhythms
• exposure to bright light prior to an east-west flight decreased the time needed to readjust to local time on arrival
• sleep-wake cycle and BRAC of 2 groups compared over 5 weeks. group 1= normal, warm artificial light and group 2=artificial blue light. 1 synchronised with natural list of dawn but 2 synchronised to office hours