Biological rhythms

Question 1

Define biological rhythms

Answer 1

cyclical activity which is a characteristic of all animal life
-the study of biological rhythms is called chronobiology

Question 2

Define circadian rhythm

Answer 2

endogenously generated rhythms with a period close to 24 hours

Question 3

Define diurnal rhythm

Answer 3

a circadian rhythm that is synchronized with the day/night cycle

Question 4

Define ultradian rhythm

Answer 4

Biological rhythms with a period much shorter that that of a circadian rhythm

Question 5

Define infradian rhythm

Answer 5

biological rhythm with a cycle of more than 24 hours

eg- the human menstrual cycle

Question 6

Name the internal control of biological rhythms

Answer 6

endogenous pacemaker (body clocks)

Question 7

Name the external control of biological rhythms

Answer 7

Exogenous zeitgebers-these are rhythmically occuring natural phenomenon which acts as a cue to regulate circadian rhythm

Question 8

what experiment occured in 1729 in correspondance to circadium rhythm?

Answer 8

de mairan experiment with mimosa pudica plant

-plant put in total darkness continued to open and close flowers

Question 9

What experiment occured in 1938 in corrospondence to ciradian rhythm?

Answer 9

-professor nathianel kleitman and bruce richardson spent 32 days underground in a cave

-no natural sunlight
-measured body temperature, urine output. eating habits and sleeping patterns

Question 10

What are the results from the 1938 circadian rhythm experiments?

Answer 10

-despite no daylight or other external cues to the world they maintained a regular sleep-wake cycle.
-humans have an endogenous circadian rhythm
-its approx 24 hours but not exactly 24 hours

Question 11

Describe body clock genes

Answer 11

-konopka and benzer discovered the period gene (PER) in drosophilla influencing biological rhythms

-research in 1960/70s concluded that natural circadian rhythm in humans was 25hrs not expected 24hrs
-length of rhythms dependent on PER3 gene

Question 12

Define chronotype

Answer 12

individuals have the propensity to sleep at different times during the day

Question 13

What is exogenous zeitgebers?

Answer 13

the most important zeitgeber is light
-these synchronize the internal body clock with external time

Question 14

What is our endogenous circadian rhythm controlled by?

Answer 14

the suprachiasmatic nucleus (SCN) which is located close to the optical nerves and this is a good position to be adjusted by sunlight.

Question 15

Describe the SCN

Answer 15

-key endogenous pacemaker
-located in the hypothalamus
-hypothalamus comprised of several nuclei
-SCN has intrinsic activity rhythm even if isolated from rest of brain
-lesion of the SCN- circadian rhytms disrupted-stephan and zucker 1972

Question 16

Describe the mutant hamster experiment

Answer 16

-Ralph et al 1990
-removed SCN from mutant hamster with natural sleep wake cycle of 21 hrs
-implanted from non mutant hamster with 24 hr cycle
-hamsters with implanted SCN changed to 21hr cycle
-concluded that SCN is the dominant endogenous pacemaker

Question 17

Describe the function of melatonin in the circadian rhythm

Answer 17

-suprachiasmatic nucleus communicates the circadian rhythm to body via melatonin production
-pineal gland stores and releases melatonin
-melatonin production increases steadily after dusk and reduces during sleep
-melatonin does not induce sleep but simply signals the start of the sleep process
-melatonin tablets can help with jet lag

Question 18

list some jet lag symptoms

Answer 18

-hypersomnolence
-headaches
-insomnia
-difficulty concerntrating
-impaired judgement
-mild nausea

Question 19

What happens when jet lag occurs?

Answer 19

-biological clock is behind local time
-body not ready for sleep
-takes longer to adjust