Lecture 5

Intro to circadian rhythms

modulated

modulated

The ultradian process is _________ by circadian and homeostatic processes

1 day

The circadian rhythm lasts how long?

living

The circadian rhythm is the rhythm of _________ organisms

stability, environment

The circadian rhythm is a dynamic balance between ________ of the system and adaptability to demands of the ________

Explain this diagram

It is the main oscillator, the circadian master clock

What function does the SCN serves?

Zeitgebers

The SCN is synchronized by what?

desynchronized

• death

If the SCN is lesioned, the body’s oscillators become ________

• We can get very thirsty or hungry during the night and it leads to _______ in animals

hypothalamus

Transplanting SCN into the ________ restores rhythms to donor’s circadian phase

• light

• dilation

• melatonin

• Projects

Characteristics of retinal ganglion cells:

• Contain melanopsin: a ________-sensitive protein

• Control pupil _______

• Produces ________

• ________ to SCN and VLPO

• higher

• firing

Retino-hypothalamic tract:

• Need ________ intensity light than cones

• After the light is off, it keeps _______ for some time

• light

  • environment

IPRGC:

• Slow and progressive response to _______

  • Why? Because we go from light to darkness all the time in our ________

melatonin

Blue light: stimulates retinal ganglion cells → SCN → pineal gland → supresses _______

Light Source	Melatonin Suppression
LED bulb	80%
Incandescent bulb	40%
Candle	2%
Candle-light-style OLED	< 2%

Light sources and melatonin suppression

Light Source	Melatonin Suppression
LED bulb
Incandescent bulb
Candle
Candle-light-style OLED

Hierarchical organization:

Hours associated with physiological responses in humans

Time giver

What does Zeitgeber means?

• entrainment

• phase

Zeitgebers:

• Participate in circadian _______

• Their effect depends on the circadian _______ of the organism

1. Light

2. Food

3. Activity-rest patterns

4. Social cues (ex: everyone going to sleep)

What are the principal Zeitgebers ranked from most important to less important?

• pineal

• SCN

• darkness, light

• opposing

Characteristics of melatonin:

• Hormone secreted by the _________ gland

• Acts on the _______

• Stimulated by _______ and suppressed by _______

• Has an _________ action with cortisol

• Correlated with body temperature, blood pressure, and growth hormone

• less

• more

Melatonin has different seasonal patterns:

• Summer = _______ melatonin produced

• Winter = ______ melatonin produced

• breeding

• immune

The functions of melatonin:

• Regulates ________ patterns in animals

• Involved in _______ function

Winter

In which season do we sleep more in Canada?

planetary

Our biological rhythms are adapted to our ________ movement (day/night)

Because our circadian rhythm tells us to sleep but our homeostatic pressure is low

If we go to sleep at 5 A.M., we will have a hard time going to sleep in the evening. Why?

own, SCN

Many organs and peripheral tissues have their _______ circadian clocks but they are subordinate to the ________

lot

At 6 A.M., we have a _______ of cortisol and melatonin so that we can be able to wake up eventually

nightmares

Cortisol increases in the morning could be an explanation for ________

placebo

Sleep is really susceptible to the _______ effect

adaptation

When the circadian phase is shifted by an advance or delay in light exposure, there is a gradual _______ over a few days