7120 Lecture Notes - Lecture 7: Circadian Rhythm, Circadian Clock, Pineal Gland
21 Jun 2018
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Lecture 7: Wakefulness and Sleep (Ch 8)
Endogenous circadian rhythms
- All animals produce endogenous circadian rhythms, internal mechanisms that operate on an
approx. 24 hour cycle
oSleep cycle
oFrequency of eating and drinking
oBody temperature
oSecretion of hormones
oUrination
oSensitivity to drugs
Endogenous circannual rhythms
- Some generate endogenous circannual rhythms, internal mechanisms that operate on an
annual or yearly cycle
oEg birds migratory patterns, animals storing food in the winter
The biological clock
- Purpose of circadian rhythm is to keep our internal workings in phase with the outside world
- The human circadian clock generates a rhythm slightly longer than 24 hours when it has no
external cue to set it
- Resetting our circadian rhythm is sometimes necessary
- Zeitgeber: german meaning ‘time giver’ – refers to the stimulus that resets the circadian
rhythm
oEg: sunlight, tides, exercise, meals, temp of environment
oDepression, irritability and impaired job performance are effects of using something
other than sunlight as a zeitgeber
Jet lag
- Refers to the disruption of the circadian rhythms due to crossing time zones
oStes from a mismatch of the internal circadian clock and external time
oSleepiness during the day, sleeplessness at night and impaired concentration
- Traveling west “phase-delays” of our circadian rhythms
- Traveling east “phase-advances” our circadian rhythms
oWant to sleep and awaken earlier
oTravel ‘back’
- What resets the clock?
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oAbsence of sunlight
oNo it’s the actual sunlight
Shift work
- Sleep duration depends on when one goes to sleep
- Working at night does not reliably change the circadian rhythm
- People adjust best to night work if they sleep in a very dark room during the day and work
under very bright lights at night
Morning people and evening people
- Cycles can differ between people and lead to different patterns of wakefulness and alertness
- Change as a function of age
oYoung children are morning people
oAdolescents are often night people
- As an adult, it partially depends on genetics
Mechanisms of the biological clock
- Mechanisms of the circadian rhythms
oThe suprachiasmatic nucleus
oGenes that produce certain proteins
oMelatonin levels
The suprachiasmatic nucleus
- Main control centre of circadian rhythms of sleep and temperature
oLocated above the optic chiasm and part of the hypothalamus
- Damage to the SCN results in less consistent body rhythms that are no longer synchronized
to environmental patterns of light and dark
- The scn
oGenerates circadian rhythms in a genetically controlled , unlearned manner
oSingle cell extracted from the SCN and raised in tissue culture continues to produce
action potential in a rhythmic pattern
oVarious cells communicate with eachother to sharpen the circadian rhythm
The SCN and retinohypothalamic Path
- Light resets the SCN via a small branch of the optic nerve known as the retinohypothalamic
path
oTravels directly from the retina to the SCN
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- The retinohypothalamic path comes from special ganglion cells that have their own
photopigment called melanopsin
oThe cells respond directly to light and do not require any input from the rods or
cones
The biochemistry of circadian rhythm
- Two types of genes are responsible for generating the circadian rhythm
oPeriod: produce proteins called PER
oTimeless: produce proteins called TIM
- PER and TIM proteins inc activity of certain kinds of neurons in the SCN that regulate sleep
and waking
oMutations in the PER gene result in odd circadian rhythms or decreased alertness if
deprived of a good nights sleep
Melatonin
- The SCN regulates the pineal gland an endocrine gland located posterior to the thalamus
- The pineal gland secretes melatonin, a hormone that increases sleepiness
- Melatonin secretion usualy begins two to three hours before bedtime
- It feeds back to reset the biological clock through its effects on receptors in the SCN
- If taken in the afternoon it can phase advance the internal clock and can help you to sleep
Sleep
- Sleep is a state that the brain actively produces
oCharacterized by a moderate dec in brain activity and decreased response to stimuli
- Sleep differs from the following states
oComa, vegetative state, minimally conscious state, and brain detah
Stages of sleep
- The EEG allowed researchers to discover that there are various stages of sleep
oAllows researchers to compae brain activity at different times during sleep
- A polysomnography is a combination of EEG and eye movement records
- Stage 1
oAlpha waves are present when one begins a state of relaxation
oStage 1 sleep is when sleep has just begun
The EEG is dominated by irregular, jagged and low voltage waves
Brain activity begins to decline
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
All animals produce endogenous circadian rhythms, internal mechanisms that operate on an approx. 24 hour cycle: sleep cycle, frequency of eating and drinking, body temperature, secretion of hormones, urination, sensitivity to drugs. Some generate endogenous circannual rhythms, internal mechanisms that operate on an annual or yearly cycle: eg birds migratory patterns, animals storing food in the winter. Purpose of circadian rhythm is to keep our internal workings in phase with the outside world. The human circadian clock generates a rhythm slightly longer than 24 hours when it has no external cue to set it. Refers to the disruption of the circadian rhythms due to crossing time zones: stes from a mismatch of the internal circadian clock and external time, sleepiness during the day, sleeplessness at night and impaired concentration. Traveling east phase-advances our circadian rhythms: want to sleep and awaken earlier, travel back". What resets the clock: absence of sunlight, no it"s the actual sunlight.
