L14 - Biological rhythms

Question 1

How do organisms on earth adapt to the cyclical changes?

Answer 1

• Passively/retroactively e.g Homeostatic mechanisms
• Proactively e.g Biological timekeepers

Question 2

What are examples of things effected by circadian rhythms?

Answer 2

• Body temperature
• Hormone secretion (e.g. melatonin, cortisol)
• Locomotor activity
• Sleep
• Alertness/cognitive performance
• Muscle strength
• Immune function

Question 3

What provides a simple way of
studying circadian rhythms in the wild and in the lab?

Answer 3

Monitoring Voluntary activity

Question 4

What does rodent wheel-running activity display?

Answer 4

A near-24h ‘free-running’ rhythm in constant conditions

Question 5

What are rodent wheel-running activity rhythms are synchronised (‘entrained’) to?

Answer 5

24h light dark cycles

Question 6

What can Rodent wheel-running activity rhythms can adapt to?

Answer 6

Changes in environmental conditions e.g timing of light and dark cycle

Question 7

What do Physiological and behavioural rhythms anticipate?

Answer 7

Changes in the environment

Question 8

What 3 principals are necessary for a circadian rhythm to exist?

Answer 8

A pacemaker
A way to synchronise to environmental cues
Effector mechanisms

Question 9

What is the main circadian clock?

Answer 9

Suprachiasmatic Nuclei (SCN) of the Hypothalamus

Question 10

What is seen in a human
with SCN damage?

Answer 10

Disrupted sleep rhythms

Question 11

What does the SCN exhibit?

Answer 11

Daily Rhythms in Metabolic Activity

Question 12

What is significant about the neurons in the SCN?

Answer 12

Each neuron is an individual clock, contain an intracellular molecular clock

Question 13

How does the SCN cells intracellular molecular clock work?

Answer 13

A transcriptional/translational feedback loop comprising of stimulatory elements (CLOCK/BMAL1) which drive inhibitory elements (PERIOD/CRYPTOCHROME)

Question 14

Where does the SCN receive light information from?

Answer 14

via the retinohypothalamic Tract (RHT)

Question 15

What regulates the melatonin release from the Pineal Gland?

Answer 15

Light and circadian signals from the SCN

Question 16

What does light do to melatonin release?

Answer 16

Light rapidly supresses melatonin release

Question 17

What does melatonin do?

Answer 17

Melatonin acts on receptors across the brain and body, allowing the SCN to convey time of day signals to other tissues

Question 18

What does a lesioned SCN do to evolutionary fitness and mortality rates?

Answer 18

Lowers evolutionary fitness
Increases mortality rate

Question 19

What are ultradian rhythms?

Answer 19

Biological rhythm with a period <24h

Question 20

Give two examples of ultradian rhythms

Answer 20

• Growth hormone is pulsatile every 3h
• Human sleep cycles with a 90 min period.

Question 21

What are Infradian rhythms?

Answer 21

Biological rhythm with a period >24h

Question 22

Give 3 examples of infradian rhythms

Answer 22

• bird migration
• reproductive cycles
• hibernation

Question 23

Give 2 examples of circannual rhythms

Answer 23

• squirrel hibernate every year
• male sheep testicles change in size depending on length of days i.e in winter they are bigger, ready to mate

Question 24

How long is a circatidal rhythm?

Answer 24

24.8 hours

Question 25

Give an example of a circatidal rhythm

Answer 25

Marine insect from the North Atlantic emerges from the sand and swims at high tide to feed and mate - they keep this rhythm in constant conditions