Biological rhythms

Question 1

what is biological rhythms?

Answer 1

The scientific study of biological clocks and associated rhythms called chronobiology

Some animals are diurnal , some are nocturnal and others are crepuscular- distemper variation in behaviour must reflect temporal variation in underling physiology

Question 2

Seven examples of biological rhythms

Answer 2

1. Cardiovascular and respiratory rhythm
2. Sleep wake cycle
3. Breeding seasons
4. Migration
5. Seasonal body-mass changes
6. Hibernation.
7. Fur thickens or changes colour

Question 3

Four types of biological rhythms

Answer 3

1. Circadian-cycles of day and night.
2. Circalidal- phases of the tide.
3. Circalunar-Phases of the moon.
4. Circannual- seasons of the year.

Question 4

What is entrainment?

Answer 4

The process of synchronisation of endogenous biological rhythms with a periodic cue in the environment

Question 5

Adaptive function of biological clocks

Answer 5

Essentially, to promote survival

Synchronising their activities with environmental conditions, enables them to prepare for predictable events, such as night time

Synchronising the internal physiological and biochemical processes to promote efficient functioning

Question 6

Molecular mechanisms of circadian clocks

Answer 6

Rhythmic patterns of gene expression provide the engine, underline cellular circadian clocks, although the gene involved or species-specific

Although these jeans can be expressed in many tissues throughout the body , the expression in the master circadian clock is critical for integrated temporal coordination in mammals

Question 7

Where is the molecular mechanisms of circadian clocks in mammals?

Answer 7

The suprachaismatic nuclei of the anterior hypothalamus represents the master circadian clock of the body

Any biological timekeeping systems must have an input and output system

Question 8

What does RHT stand for? (Circadian clocks)

Answer 8

Retinohypothalamic tract

Question 9

What does IGL stand for? (Circadian clocks)

Answer 9

Intergeniculate leaflet

Question 10

What does GHT stand for? (Circadian clocks)

Answer 10

Geniculohypothalamic tract

Question 11

What does PVN stand for? (Circadian clocks)

Answer 11

Paraventricular nucleui

Question 12

What does MFB stand for? (Circadian clocks)

Answer 12

Medial forebrain bundle

Question 13

What does SCG stand for? (circadian clocks)

Answer 13

Superior cervical ganglion

Question 14

What does RF stand for? (Circadian clocks)

Answer 14

Reticular formation

Question 15

What is the input system in circadian clocks?

Answer 15

Environmental light information is received from the eyes and transduced to the SCN via the RHT- this is a distinct pathway from the normal visual system

There isn’t also an indirect pathway from the GHT via the IGL

Question 16

Input systems in mice

Answer 16

Mice that lack rod and cone photo receptors still entrain to light, as well as sighted mice- but loss of photo pigment called melanopsin impairs circadian entrainment

Question 17

Two types of output signals from the SCN

Answer 17

1.Humeral diffusible signals
2.Neutral projections

Question 18

What is the humeral diffusible signal?

Answer 18

SCN neurones express several neuropeptides, such as arginine vasopressin and prokineticin-2 which than modulate physiological functions

Question 19

What are neutral projections?

Answer 19

Projections from the SCN to the PVN, through the MFB and onto the SCG postganglionic noradrenergic fibres eventually project back into the brain and innervate the pineal gland, when neutral information is transducers into a hormonal message (melatonin)

Question 20

Circannual and seasonal rhythms

Answer 20

The effects on light of daily melatonin production are critical in mammalian photoperiodism

The duration of nocturnal melatonin signal encodes day length, which can then be used to make seasonal adjustments in behaviour to coincide with environmentally conditions or resource availability

Question 21

What are the two types of hibernators?

Answer 21

1. Obligate hibernators
2. Facultative hibernators.

Question 22

What are obligate hibernators?

Answer 22

These annually enter hibernation based on seasonal time in cues regardless of ambient temperature and access to food

Question 23

What are facultative hibernators?

Answer 23

These only enter hibernation in response to stressors from the environment, for example of a cold stress, food deprived or both

Question 24

Hibernation functions

Answer 24

To conserve energy, when sufficient food is not available, so most commonly during winter months

Mammals decrease the metabolic rate and thereby the body temperature

Question 25

Hibernation- the fat tailed dwarf lemur

Answer 25

During the cool dry season, April to October when food and water availability is low the species retreat into three holes and cannot be seen for seven months which suggests they are hibernating during the Austral winter

During hibernation, most lemurs fluctuate between 10° C and 30° C closely and passively tracking diurnal fluctuations

Question 26

Seasonal coat colour moulting

Answer 26

An important adaptation for males that occupy temper and polar regions is coat colour moulting

21 species of birds and mammals, undergo complete biannual colour change from brown in the summer, to completely white in the winter

The main adaptive function of moulting is seasonal camouflage against snow- both prey and predators

Photoperiod is the main driver of the moult phenology

Question 27

Circadian and circannual variation and coat colour moulting

Answer 27

Variation in melatonin signal duration is used as a critical input signal for the pituitary gland and its pars tuberalis, which regulates seasonal prolactin secretions

Question 28

Melatonin and coat colour moulting

Answer 28

Melatonin acts as an inhibition of prolactin production, and this hormonal interaction serves as the main humeral signal controlling the phenology of many seasonal events such as migration, reproduction, and moults

Thus prolactin plays an important role in regulating the SSC moults, but the exact mechanism remains unclear