biological rhythms

circannual

yearly, migratory cycle

infradian

a day, menstrual cycle

Circadian

daily, human sleep-wake cycle

Ultradian

a day, meals, sleep cycles

4 biological rhythms

* circannual
* infradian
* cricadian
* ultradian

humans and animals have

an endogenous clock (meaning that they are regulated by the organism and not external stimuli)

zeitgeber

cues that synchronize biological rhythms

Entrainment

the process of synchronizing an endogenous biological rhythm to the rhythm of an environmental cue

suprachiasmatic nucleus

time cues

central outputs

peripheral outputs

time cues

* feeding schedules
* light
* activity

central outputs

* sleep-wake cycles
* cognitive performance

peripheral outputs

* heart
* liver
* muscle
* kidney

Contributes to physiology and behaviour

* central outputs
* peripheral outputs

Free running rhythm (has to do with circadian rhythm)

spontaneous endogenous rhythm in environments without changes in lightness

Human circadian free running rhythm

>24 hrs

During constant light or constant dark

animals express a free running circadian rhythm

entrained circadian rhythm

With exposure to sunlight during the day and darkness at nighttime, animals and humans express an

jetlag

easier to adjust when you go somewhere, harder when you come back, throws off circadian rhythm

retinohypothalamic tract (neural mechanism)

light signal is transmitted from a small population of retinal ganglion cells (neurons) to the suprachiasmatic nucleus (SCN) of the hypothalamus

– synchronize endogenous circadian rhythm with the light/dark changes in the environment

Intrinsically photosensitive retinal ganglion cells (ipRGCs) in the Retinohypothalamic Tract

– have no image-forming function, but detect brightness \n – express melanopsin, a light-sensitive substance

Loss of ipRGCs in the Retinohypothalamic Tract

exhibit free running rhythm

Suprachiasmatic Nucleus (SCN)

master oscillator of biological rhythms, part of the hypothalamus

responsible for the firing rhythms (intrinsic clock) in the SCN cells

Specific genes and transcription factors

Individual SCN neuron

fires rhythmically in a tissue culture

Clock genes

found in the SCN and in cells of other organs

SCN pacemaker

drives cells that control the rhythmic occurrence of different physiological events or behaviors (e.g., digestion, blood pressure, sleep)

neuronal activity is measured by (Circadian rhythm in the SCN)

the amount of radiolabeled 2-deoxyglucose uptake by neurons

SCN is more active (Circadian rhythm in the SCN)

during the light period

SCN cell activity is

(SCN implant)

genetically programmed

Lesions of the SCN

(SCN implant)

lead to animals with arrhythmic activity patterns

Transplant of embryonic SCN cells

(SCN implant)

restores the circadian rhythm

a Circannual Rhythm is controlled by

day length

Pineal gland (circannual rhythm)

– secretes melatonin at nighttime (dark) \n – seasonal changes in melatonin levels because longer

darkness in the winter increases the duration of melatonin secretion

SCN involvement in circannual rhythm

male hamster testosterone secretion is inhibited by the large

amount of melatonin in the winter

Transplants of embryonic SCN cells

do not restore the circannual rhythm

SAD

(Seasonal Affective Disorder)

* seasonal experience of

sadness
* interpersonal difficulties
* decreased activity
* increased sleep time
* carbohydrate craving
* increased appetite
* weight gain
* can be improved with

morning light therapy