sleep why do we sleep?. sleep is a basic requirement for normal brain function. lack of sleep –...

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Sleep Why do we sleep?

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Page 1: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

Sleep

Why do we sleep?

Page 2: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

• Sleep is a basic requirement for normal brain function. • Lack of sleep – Mental fatigue, – poor decision-making, – shortened attention span, – higher anxiety, – impaired memory, – impaired learning, – a grouchy mood and – a heightened risk of migraine and epileptic attacks .

• Chronic and complete insomnia ultimately lead to death in humans, rats, and flies alike.

Page 3: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

Total sleep deprivation

• Rats totally sleep-deprived died within 11-32 days (faster than food-deprived rats).

• All sleep deprived rats showed a debilitated appearance, lesions on their tails and paws, and weight loss in spite of increased food intake.

• Everson, C. A., Bergmann, B. M., & Rechtschaffen, A. (1989). Sleep deprivation in the rat: III. Total sleep deprivation. Sleep, 12(1), 13-21.

Page 4: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

• Sleep is universal among vertebrates and has been found in invertebrates

• The total number of hours of daily sleep varies from as much as 20 hours in bats to as little as 3 to 4 hours in giraffes and elephants

• Faster metabolism longer sleep duration• Smaller animals have faster metabolism longer sleep

Page 5: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

• In waking, CSF flow is restricted to the brain surface—but expands deep into the tissue during both slow-wave sleep and anesthesia. The consequence is remarkable: The flow of CSF through the interstitial space is increased 20-fold in slow sleep compared to flow of CSF during waking.

• During sleep, waste products of brain metabolism are removed from the interstitial space among brain cells where they accumulate.

Page 6: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

Conclusions:• Main function of sleep is maintenance.• Metabolism is a dirty process. • During sleep, waste products of brain metabolism are

removed from the interstitial space.• During sleep there is also increased production of

oligodendrocytes repair axons.

Page 7: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

Sleep and memory

• Sleep is good for memory consolidation (conversion of memory into permanent memory).

• Memory improvement is most dramatic for procedural memory (riding a bike, skating, playing the piano).

• Even a short nap can really improve memory.

Researchers trained mice in a new skill - walking on top of a rotating rod

sleeping mice formed significantly more new connections between neurons

Page 8: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

• Important memories are consolidated. • Unimportant memory traces are deleted. That

includes most memories. Synapses forming that memory are disintegrated, synaptic spines are retracted. It is very important to forget!

• Sleep is important for both • memory consolidation and • preparing the brain for new learning.

Sleep and memory

Page 9: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

Sleep stages

Non-REM sleep = slow wave sleep = deep sleep

• Sleep is highly structured• 1 complete cycle (Non-REM stage and REM stage) = 1.5hours

Page 10: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

Slow-wave (deep, non-REM) sleep• Deep sleep Loud noise, smells

are unlikely to wake up• Many neurons are synchronized

(firing together) so we see high amplitude EEG with low frequency ~1Hz.

• Muscles are not paralyzed, so sleep-walking, sleep-talking, and bedwetting occur in this stage.

• If you wake up from slow wave sleep you feel dreadful.

• When people are woken from slow-wave sleep, they usually do NOT report dreams.

Page 11: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

• During slow-wave sleep CSF flow expands deep into the brain tissue. The consequence is remarkable: The flow of CSF through the interstitial space is increased 20-fold in slow sleep compared to flow of CSF during waking.

Page 12: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

REM (Rapid Eye Movement / Paradoxical sleep)• EEG readings are irregular in frequency and

low in amplitude—similar to those observed in awake individuals.

• When people are woken from REM sleep, they usually report vivid dreams.

• Eyes move rapidly under closed lids, breathing becomes irregular and heart rate increases.

• Motor neurons are completely inhibited (so that you don’t enact your dreams; common experience: nightmare want to run but cannot move muscles).

• Horses and many other animals can sleep while standing, but must necessarily lie down for REM sleep because of inhibition of tonic muscles).

• People even lose some of the ability to regulate their body temperature during REM

Page 13: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

What causes one to fall into sleep?

• Circulating hormones?• Brain nuclei?• Accumulation of Adenosine?

Page 14: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

• Melatonin - a hormone that anticipates the daily onset of darkness

• Produced in the pineal gland.

Page 15: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened
Page 16: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

• The Hensel girls are the rarest form of conjoined twins, the result of a single fertilised egg which failed to separate properly in the womb.

• They have two spines (which join at the pelvis), two hearts, two oesophagi, two stomachs, three kidneys, two gall bladders, four lungs (two of which are joined), one liver, one ribcage, a shared circulatory system and partially shared nervous systems.

• From the waist down, all organs, including the intestine, bladder and reproductive organs, are shared.

• While they were born with three arms, one was removed surgically.

• Although Brittany - the left twin - can't feel anything on the right side of the body and Abigail - the right twin - can't feel anything on her left, instinctively their limbs move as if co-ordinated by one person, even when typing e-mails on the computer.

• It is rare for twins conjoined the way that Abby and Brittany are to survive into adulthood, but despite this they are in good health, without heart defects or organ failure.

In these sisters: One brain can be asleep while the other brain may be awake brain nuclei

Page 17: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

Adenosine / Caffeine

• Local control of alertness level• As neurons fire, they use ATP and produce adenosine. • With a continued wakeful state, over time adenosine

from ATP accumulates in synapses.• Adenosine activates adenosine receptors that

increase drowsiness. • The caffeine molecule is competitive inhibitor od

adenosin.• As a result, caffeine temporarily prevents or relieves

drowsiness, and thus maintains or restores alertness.

Page 18: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

Central control of alertness level: Reticular formation

• The reticular formation has projections to the thalamus and cerebral cortex that allow it to exert control over which sensory signals reach the cerebrum and come to our conscious attention.

• It plays a central role in states of consciousness like alertness and sleep (pacemaker for slow sleep Delta waves).

• Injury to the reticular formation can result in irreversible coma.

• Reticular formation in brainstem is important for setting alertness level

Page 19: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

Neuropeptide Orexin – the ultimate flip flop switch between sleep and wakefulness

• Orexin is neurotransmitter released in hypothalamus by a small nucleus that consist of 10,000 to 20,000 neurons.

• Orexin strongly excites various brain nuclei important in wakefulness.

• Orexin-producing cells integrate metabolic, circadian and sleep debt influences to determine whether an individual should be asleep or awake.

• Central administration of orexin-A strongly promotes wakefulness, increases body temperature and locomotion, and elicits a strong increase in energy expenditure.

• Insomniacs taking an orexin blocker, suvorexant, fell asleep faster and slept an hour longer.

Page 20: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

“Orexin flip flop switch”

System that promotes sleep

System that promotes wake

• The most common form of narcolepsy, in which the sufferer briefly loses muscle tone (cataplexy), is caused by a lack of orexin in the brain due to destruction of the cells that produce it.

• Narcolepsy results in excessive daytime sleepiness, inability to consolidate wakefulness in the day (and sleep at night), and cataplexy, which is the loss of muscle tone in response to strong, usually positive, emotions.

• One woman in England has been declared dead three times and once woke up in morgue.

• Example: http://youtu.be/qVu-IcLoZtU

Page 21: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

What causes one to fall into sleep?

• Circulating hormones? – Yes. E.g. melatonin• Brain nuclei? – Yes. E.g. Reticular formation• Accumulation of Adenosine? – Yes.• Conclusion: all of the above with the Orexin

switch

Page 22: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

Circadian rhythm

• Circadian rhythm = 25.3h• This might explain why it is

easier to travel west, compared to jetlag problems associated with traveling east.

• Optimal travel: go west and cross one time zone a day

Page 23: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

• Photosensitive cells in the retina control the 24-hour cycle of several subcortical nuclei, that, in turn, control the pineal gland.

• Interestingly: most organs, even cells in the body have their own 24-hours clocks

• Melatonin anticipates the daily onset of darkness – central control of local circadian rhythms

• Melatonin is safe aid for falling into sleep. Jetlag – take melatonin

Page 24: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

Disorders of sleep• Slow sleep

– Sleepwalking• Can be triggered by stress, alcohol and sleep deprivation• Individual may engage in complex behavior while sleepwalking

– Sleep talking– Bedwetting

• REM Sleep Behavior Disorder– Muscles are NOT inhibited physical activity during REM sleep:

• Dream about diving and dive from bed • Dream about playing football and tackle a bed partner

– Often associated with a neurological disorder or a tumor• REM Sleep paralysis:

– Muscles are inhibited but the brain is almost awake• Some people think they are abducted by aliens and strapped down for probing.

• Narcolepsy– Narcolepsy results in excessive daytime sleepiness, inability to consolidate

wakefulness in the day (and sleep at night), and cataplexy when individual suddenly falls asleep (into REM sleep, with all their skeletal muscles paralyzed)

Page 25: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

Sleep apnea

• is a sleep disorder characterizedby pauses in breathing during sleep.

• Each pause in breathing for several seconds can wake you up.

• Result: lack of normal continuous sleep sleepiness during the day, lack of attention, spontaneous nap.

• Common in middle aged overweight people (prevalence in men over 25%), very high in truck drivers.

Page 26: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

micro-sleep

• Sleep-deprived humans will fall in micro-sleep. One part of the brain falls asleep, while the rest of the brain is active.

• While driving you might miss sensory information from the red light or a car in front of you, even when the rest of the brain (motor cortex) is not sleeping and is able to drive the car.

Page 27: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

REM is essential

• During 1970s the main hypnotic (from Greek Hypnos =sleep: drugs that induce sleep) drugs were barbiturates

• Prescribed to treat insomnia, barbiturates are agonists of ionotropic GABA receptor • Ethanol, barbiturates, benzodiazepines all increase conductance of ionotropic GABA receptor • Barbiturates significantly reduce the amount of REM sleep • Abrupt withdrawal of barbiturates results in REM rebound in terrible nightmares• Barbiturates have now largely been replaced by safer benzodiazepines (triazolam, flurazepam)

Barbituric acid, the basic structure of all barbiturates

The core structure of benzodiazepines.

Page 28: Sleep Why do we sleep?. Sleep is a basic requirement for normal brain function. Lack of sleep  – Mental fatigue, – poor decision-making, – shortened

Short daytime naps

• Consist of deep slow wave sleep, • In the early phases of deep sleep

people report vivid hallucinations that are shorter, more static and more thoughtlike than the dreams that occur during REM sleep.

• These visions are typically more like snapshots than narratives and do not include a self.

• Even a short nap can really improve memory