Lecture 8 - Sleep 1: What is sleep? Flashcards
Circadian rhythm define
A circadian rhythm is a natural, internal process that regulates the sleep-wake cycle and repeats on each rotation of the earth roughly every 24 hours
Wake maintenance zone
7-9pm
Optimum sleep period
11pm-7am
Wake up zone
8am-12pm
Melatonin
makes you feel tired therefore starts rising from 9pm and then lowers at 7 am
Melatonin is a hormone primarily released by the pineal gland at night, and has long been associated with control of the sleep–wake cycle.
Sleep wake cycle is an example of
a circadian rhythm
Is the sleep wake cycle driven by biological or social factors?
Individuals tend to be active for a block of time and then sleep for a block of time
Yes we do have an internal body clock but it does not exactly keep time with the external time and it runs on a roughly 25 hour time
Michel Siffre experiment
Sleep/wake cycle if we were deprived of all information about the time of day
Staying in a cave for two months and what he found is that he lost track of time (whilst in the cave he was not actively counting the days or anything to try keep track) and at the end of the two months when he was asked to come out he had though that he was only in there for one month
Whilst in there he could go to sleep whenever he wanted and when he woke he would turn his light on and then call the rest of the team on the outside and give them his pulse as a daily health check and he would also count to 120 and he was to count each number per second and what they found is that by the end of the two months he was counting 120 in five minutes rather than 2, his estimate of time really changed
It was found that his day length and sleep time stretch out so by the end of the experiment he found that his day night cycle was about 24.5 yours and therefore it meant that he got out of sync with the environment
This experiment shows that despite being out of sync with the environment our bodies still go to sleep for roughly the same amount of time (8-8.5 hours)
Graph shows that without external cues you slowly get out of sync with the environment
Suprachiasmatic nucleus of the hypothalamus (SCN)
A region that cycles on the roughly 24 hour cycle is the suprachiasmatic nucleus of the hypothalamus (SCN)
Internal body clock that will keep the body cycling (being active and going to sleep) on a roughly 24 hour period even if you are deprived of external cues and this structure right at the base of the brain is called the SCN
Hypothalamus is involved in controlling body temperature, sexual activity, thirst and other essential functions, suprachiasmatic nucleus means that it is a nucellus of that structure and it is located above the optic chasm so the optic nerve from the eye runs in under the brain and crosses over and suprachiasmatic means that it is located above this cross
If you have damage on this nucleus then you no longer cycle on a roughly 24 hour period
Pineal gland and SCN relationship
Pineal gland releases the hormone melatonin at night, the suprachiasmatic nucleus sends signals to the pineal gland to release melatonin
What does the pineal gland release?
Melatonin
Effect of SCN removal on sleep patterns
without the SCN sleep in small little patches over a 24 hour period, lost the cycle but still get similar amount of sleep and active time just separated more
What normally keeps out sleep-wake clock on time?
Light controls the body clock by activating the SCN
SCN gets it through information that is coming through the eyes, there are specialised receptors called melanopsin receptors that respond to levels of light and dark and these receptors send information directly to the SCN which then controls the release of melatonin from the pineal glands
People who are functionally blind - if their melanopsin receptors are still intact then they can still respond to the levels of light and get the same cycle as other people
Light is the primary
zietgeber (time giver)
Light as a time giver…what are the other ones
(also exercise, food, social contacts)
Resetting the circadian rhythm
Resetting the circadian rhythm
Normally about one hour per day
How can you speed this up?
Shift work = for most people it is easier to phase delay (wake up later) than to phase advance (wake earlier) i.e. go to a later shift
Jet lag = start shifting gradually several days before your trip, travel west rather than east (days are longer), use exposure to bright light and excercise to speed up shift - drugs such as melatonin?
Why do we need sleep?
The core function of sleep is to adapt animals to their specific environmental niche - wondering in the dark is a waste of energy when there is very little chance of finding food and we are likely to be preyed upon by larger animals so it is though that through evolution we have evolved to shut down at night to remain safe (remain quiet during periods of vulnerability? - it is always safer to be concisous in order to react to an emergency even if lying still in the dark at night. Thus there does not seem to be any advantage of being unconscious and asleep if safety is paramount)
Animals that eat vegetation and therefore essentially have to be eating all the time do not sleep for very long in order to acquire enough energy
Carnivores such as tigers are predators and are not very vulnerable when they are sleeping due to the hierarchy
Results of sleep deprivation - Peter Tripp (1959)
201 hours which is 8 days
Psychosis
Sleep deprivation - (radio show, 201hrs) displays mental disorder symptoms, paranoia.
Results of sleep deprivation - Randy Gardener (1964)
264 hours which is 11 days
Some impairment in attention, motivation, cognition but transient and only 6 hours extra sleep in the following week
Results of sleep deprivation - Animal studies
After 2 weeks unable to thermoregulate, lost weight, infections.
After 4 weeks - death
Recuperation/repair theory
Predictions of a recuperation theory:
A) sleep deprivation should produce physiological and psychological disturbances
B) these disturbances should get worse as deprivation continues
C) After deprivation much of the sleep debt will be recovered
Shift work - link to cancer, diabetes, cardiovascular risks, obesity, mood disorders and age related macular degeneration
Another theory of why do we sleep - sleep increases chromosome dynamics to reduce accumulating DNA damage
Zebrafish embryo (transparent so can see what is going on)
Graph shows chromosomes moving around at night
One proposed function of sleep is getting these DSBs fixed
Double stranded breaks which is damage to the DNA, there is an accumulation of DSBs and when they accumulate to a certain level it sends a signal to the nervous system that it needs to sleep, and once you do to sleep you get the movement of the chromosomes which then repairs the breaks in the DNA
