Biological Clocks - created from Mind Map

Rhythms Daily Rhythms Annual Rhythms Tidal Rhythms Lunar Rhythms Compound Rhythms Nocturnal Diurnal Crepuscular Semi-lunar Rhythm

Internal and External stimuli Endogenous rhythms Exogenous Rhythms Internal clocks Circadian other C.rhythms

Entrainment Zeitgeber Phase shifting

Time sense

Location Animals Birds Insects

Mechanisms of Entrainment

Most animals are active during restricted parts of the day-night cycle.

Nocturnal-active at night

Day active

Active at dawn and dask

These are associated with the combined effects of the earth orbiting the sun and the Earth's 23.45 degree axial tilt causing seasonal cycles. Both animals and plants show this rhythm and are triggered by changes in photoperiod (day length). Migration and hibernation in animals and leaf fall and germination in plants are examples.

This is caused by the gravitational pull of the moon (and sometimes sun). There are two tides a day due to the water pile up towards and away from the moon. Organisms living near the middle of the tidal zone alternately inhibits two environments land and sea. For most shore organisms, immersion by the sea is the time for feeding and reproduction. While when the tide is out the activity cease. Organisms feed on material deposited by outgoing tide.

Lunar rhythms are linked to the rotation of the moon  around the earth, and are much less common than other rhythms

two cycles every month every 15 days the high tides are at their highest and these spring tides occur a few days after the new and full moon. This is when the sun and the moon's gravitational pulls reinforce each other.

Rhythms can be affected by other rhythms.

Internal clock independent of environmental changes. The setting of the clock is sometimes adjusted by external reasons

Externally driven rhythms. Driven by external stimuli . For example the germination of seeds in deserts uses the timing of rain fall.

When a rhythm is in constant environmental conditions, it is said to be free running as it is unaffected by external time cues. It's period doesn't correspond exactly with the period of the environmental rhythm.

Because the free running period of daily endogenous rhythms is never quite 24 hours, they are said to be circadian. Circalunar, circatidal, circasemilunar and circannual rhythms

Endogenous rhythms don't usually coincide with the environment, showing that under natural conditions the internal clock must be continually entrained by the environment. Entrainment- process by which an internal clock becomes reset by rhythmic environmental influences.

Zeitgeber is the environmental cue use to "set" the clock. Zeitgeber- external environmental cue by which an internal cue is reset.

Entrainment involves the process of phase shifting, in which the time of the pecks of an endogenous rhythm are advanced or retarded

Stomata show rhythmic changes in aperture with a period of about 24 hours. Unicellular algae the rate of photosynthesis is about 24hours

Continuously consulted clocks are also used in solar navigation in many animals. The sun can be used as a compass if its apparent movement during the day can be accounted for, which requires an accurate clock

It is centred in the hypothalamus called the supra-chiasmatic nuclei.

The clock is centred in the pineal

The oscillator is located in the brain

Detection of the external rhythm using some form of zeitgeber. Transmission of a signal from the receptor to the clock mechanism. A change in the phase clock.

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Biological Clocks

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