Biological rhythms Flashcards
what is biological rhythms?
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
Seven examples of biological rhythms
- Cardiovascular and respiratory rhythm
- Sleep wake cycle
- Breeding seasons
- Migration
- Seasonal body-mass changes
- Hibernation.
- Fur thickens or changes colour
Four types of biological rhythms
- Circadian-cycles of day and night.
- Circalidal- phases of the tide.
- Circalunar-Phases of the moon.
- Circannual- seasons of the year.
What is entrainment?
The process of synchronisation of endogenous biological rhythms with a periodic cue in the environment
Adaptive function of biological clocks
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
Molecular mechanisms of circadian clocks
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
Where is the molecular mechanisms of circadian clocks in mammals?
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
What does RHT stand for? (Circadian clocks)
Retinohypothalamic tract
What does IGL stand for? (Circadian clocks)
Intergeniculate leaflet
What does GHT stand for? (Circadian clocks)
Geniculohypothalamic tract
What does PVN stand for? (Circadian clocks)
Paraventricular nucleui
What does MFB stand for? (Circadian clocks)
Medial forebrain bundle
What does SCG stand for? (circadian clocks)
Superior cervical ganglion
What does RF stand for? (Circadian clocks)
Reticular formation
What is the input system in circadian clocks?
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
Input systems in mice
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
Two types of output signals from the SCN
1.Humeral diffusible signals
2.Neutral projections
What is the humeral diffusible signal?
SCN neurones express several neuropeptides, such as arginine vasopressin and prokineticin-2 which than modulate physiological functions
What are neutral projections?
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)
Circannual and seasonal rhythms
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
What are the two types of hibernators?
- Obligate hibernators
- Facultative hibernators.
What are obligate hibernators?
These annually enter hibernation based on seasonal time in cues regardless of ambient temperature and access to food
What are facultative hibernators?
These only enter hibernation in response to stressors from the environment, for example of a cold stress, food deprived or both
Hibernation functions
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
Hibernation- the fat tailed dwarf lemur
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
Seasonal coat colour moulting
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
Circadian and circannual variation and coat colour moulting
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
Melatonin and coat colour moulting
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
