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Chapter 6: Sleep

In this Chapter:

  • Brain Activity during Sleep

  • Sleep disorders

  • How is sleep regulated?

  • The Sleep-Wakefulness Cycle

Introduction

  • Lack of sleep increases the risk of many health problems including:

    • Diabetes

    • Cardiovascular disease

    • Heart attacks

    • Stroke

    • Depression

    • High Blood Pressure/Hypertension

    • Obesity

    • Infections

  • Sleep is made of several different stages that are accompanied by daily rhythms in hormones, body temperature, etc.

  • Sleep disorders are one of the least recognized sources of disease, disability, and death

Brain Activity During Sleep

  • Electroencephalography (EEG): the measurement of electrical activity in different parts of the brain and the recording of such activity as a visual trace (on paper or on an oscilloscope screen).

  • One sleep cycle is approximately 90 minutes

  • Each night, the brain progresses through a series of stages when brain waves slow down for 60 minutes in NREM (non-rapid eye movement) sleep

    • This is accompanied by the relaxation of muscles and eyes

    • Heart rate, Blood pressure, and body temperature fall

    • If awakened in this stage of sleep, most people only recall fragments of thought

    • NREM sleep: sleep where the eyes do not rapidly move

  • Over the next half-hour, brain activity changes to REM sleep

    • REM (Rapid Eye Movement) sleep: sleep characterized by the random rapid movement of the eyes when derams also occur

    • Characterized by neocortical (in the neocortex) EEG waves similar to those when a person is awake

    • REM is accompanied by atonia

      • Atonia: paralysis of muscle

    • Dreaming occurs only in REM sleep

      • The first REM period lasts 10-15 min

  • Over the course of one’s lifetime: slow-wave sleep time decreases & REM time increases

  • Overall sleeping time at different life stages:

    • Infants: up to 18 hrs

    • Older adults: 6-7 hrs

      • Less time sleeping in general and in slow wave sleep specifically

Sleep Disorders

  • Insomnia: the most common sleep disorder where individuals have trouble falling asleep

    • Some people have problems falling asleep, some wake up in the middle of the night and can’t fall asleep again

    • Sleeping drugs do not help because they suppress slow-wave sleep and aren’t effective in keeping people asleep

  • Many common disorders disrupt deeper stages of sleep

  • Excessive daytime sleepiness has many causes

    • Obstructive Sleep Apnea: airway muscles relax and close airway causing difficulty breathing

      • individual wakes up without entering deeper stages of slow-wave sleep.

      • Causes high blood pressure and increases the risk of heart attack

      • more daytime sleepiness

    • Periodic Limb Movements: intermittent jerks of the legs or arms that occur as individual enters slow wave sleep and cause arousal from sleep.

    • REM behavior disorder: occurs when muscles fail to become paralyzed during REM sleep

      • Act out dreams by getting up and moving around.

      • Can be very disruptive.

    • Both periodic limb movements and REM behavior disorder are more common in people with Parkinson’s disease.

      • Can be treated with drugs for Parkinson’s or with a benzodiazepine called clonazepam

  • Narcolepsy: mechanisms controlling transitions into sleep (particularly REM sleep) don’t work.

    • Narcolepsy is caused by the loss of nerve cells in lateral hypothalamus that contain orexin/hypocretin.

      • Have sleep attacks during day (suddenly fall asleep).

      • Hypnagogic hallucination: individuals tend to enter REM sleep very quickly and enter dreaming state while partially awake

      • Cataplexy: loss of muscle tone similar to what happens in REM sleep but occurs when the individual is still awake

How is Sleep Regulated?

  • Wakefulness is maintained by systems in the upper brainstem and hypothalamus

    • Neurons here use acetylcholine, norepinephrine, serotonin, glutamate to connect with the forebrain

    • Neurons in the hypothalamus use orexin and some contain histamine

    • Thalamus and basal forebrain activation by acetylcholine is very important too

      • basal means “closest to midbrain/base”

  • Level of alertness can be shown in an activated low-volt EEG

  • Arousing systems are less active in non-REM sleep

    • Transmission of information to the thalamus is limited

  • Ventrolateral preoptic (VLPO) nucleus: area in the brain that causes suppression of arousal systems

    • VLPO nucleus neurons have the inhibitors galanin and GABA

    • Damage to the VLPO area produces irreversible insomnia

  • In REM sleep, there is an internally activated brain and EEG but the external input is suppressed

    • Internal activation comes from cyclically active REM sleep generator neurons in the brainstem

  • Signals from neurons cause the excitation of the forebrain

    • Leads to rapid eye movements & muscle suppression

  • Forebrain excitation driving force behind dreams of REM sleep

  • Motor cortex neurons fire as rapidly during REM sleep as during waking movement

    • Explains movement coinciding with dreams

  • Periodic recurrence of REM sleep

    • REM sleep occurs every 90 min during sleep

    • This is caused by on-and-off switching of REM-generators (acetylcholine, glutamate) and REM-suppressors (norepinephrine, serotonin, GABA)

The Sleep-Wakefulness Cycle

  • 2 determining factors for sleepiness:

    • Circadian system: Monitoring the time of day/night

    • Homeostatic system: monitoring how long the person is awake

  • Circadian system is regulated by the suprachiasmatic nucleus

    • Suprachiasmatic nucleus: a small group of cells in the hypothalamus serving as the master clock

      • It expresses clock proteins that go through a biochemical cycle of approximately 24 hrs

      • This sets the pace for daily cycles of activity, sleep hormone release, etc.

  • The suprachiasmatic nucleus also receives input from the retina

    • The clock can be reset by light so it is linked to the outside day-night cycle

  • Also provides information to the subparaventricular nucleus → dorsomedial nucleus → VLPO and orexin neurons

    • Orexin: an excitatory signal to arousal system especially norepinephrine neurons

      • Orexin activation plays role in preventing transitions into REM sleep during the day

  • Arousal mediated by orexin and activation of norepinephrine neurons in the locus coeruleus

    • Locus coeruleus: a lateral part of brain stem that has norepinephrine producing neurons that mediate arousal along with orexin

  • The homeostatic system responds to longer wake periods by increasing the urge to sleep

    • The longer a person is awake, the greater the likelihood of an increase in sleep-inducing factors

  • Adenosine: a very important sleep promotor

    • More adenosine means increased sleepiness

    • Adenosine release starts in the basal forebrain and spreads to the rest of the cortex

    • Increased adenosine levels slow down cellular activity and diminish arousal

    • Adenosine levels decrease during sleep

  • Brain adenosine may be produced by ATP breakdown over the course of wakefulness

  • Neuron activity decreases and adenosine levels decline in non-REM sleep

    • ATP levels increase during sleep

Chapter 6: Sleep

In this Chapter:

  • Brain Activity during Sleep

  • Sleep disorders

  • How is sleep regulated?

  • The Sleep-Wakefulness Cycle

Introduction

  • Lack of sleep increases the risk of many health problems including:

    • Diabetes

    • Cardiovascular disease

    • Heart attacks

    • Stroke

    • Depression

    • High Blood Pressure/Hypertension

    • Obesity

    • Infections

  • Sleep is made of several different stages that are accompanied by daily rhythms in hormones, body temperature, etc.

  • Sleep disorders are one of the least recognized sources of disease, disability, and death

Brain Activity During Sleep

  • Electroencephalography (EEG): the measurement of electrical activity in different parts of the brain and the recording of such activity as a visual trace (on paper or on an oscilloscope screen).

  • One sleep cycle is approximately 90 minutes

  • Each night, the brain progresses through a series of stages when brain waves slow down for 60 minutes in NREM (non-rapid eye movement) sleep

    • This is accompanied by the relaxation of muscles and eyes

    • Heart rate, Blood pressure, and body temperature fall

    • If awakened in this stage of sleep, most people only recall fragments of thought

    • NREM sleep: sleep where the eyes do not rapidly move

  • Over the next half-hour, brain activity changes to REM sleep

    • REM (Rapid Eye Movement) sleep: sleep characterized by the random rapid movement of the eyes when derams also occur

    • Characterized by neocortical (in the neocortex) EEG waves similar to those when a person is awake

    • REM is accompanied by atonia

      • Atonia: paralysis of muscle

    • Dreaming occurs only in REM sleep

      • The first REM period lasts 10-15 min

  • Over the course of one’s lifetime: slow-wave sleep time decreases & REM time increases

  • Overall sleeping time at different life stages:

    • Infants: up to 18 hrs

    • Older adults: 6-7 hrs

      • Less time sleeping in general and in slow wave sleep specifically

Sleep Disorders

  • Insomnia: the most common sleep disorder where individuals have trouble falling asleep

    • Some people have problems falling asleep, some wake up in the middle of the night and can’t fall asleep again

    • Sleeping drugs do not help because they suppress slow-wave sleep and aren’t effective in keeping people asleep

  • Many common disorders disrupt deeper stages of sleep

  • Excessive daytime sleepiness has many causes

    • Obstructive Sleep Apnea: airway muscles relax and close airway causing difficulty breathing

      • individual wakes up without entering deeper stages of slow-wave sleep.

      • Causes high blood pressure and increases the risk of heart attack

      • more daytime sleepiness

    • Periodic Limb Movements: intermittent jerks of the legs or arms that occur as individual enters slow wave sleep and cause arousal from sleep.

    • REM behavior disorder: occurs when muscles fail to become paralyzed during REM sleep

      • Act out dreams by getting up and moving around.

      • Can be very disruptive.

    • Both periodic limb movements and REM behavior disorder are more common in people with Parkinson’s disease.

      • Can be treated with drugs for Parkinson’s or with a benzodiazepine called clonazepam

  • Narcolepsy: mechanisms controlling transitions into sleep (particularly REM sleep) don’t work.

    • Narcolepsy is caused by the loss of nerve cells in lateral hypothalamus that contain orexin/hypocretin.

      • Have sleep attacks during day (suddenly fall asleep).

      • Hypnagogic hallucination: individuals tend to enter REM sleep very quickly and enter dreaming state while partially awake

      • Cataplexy: loss of muscle tone similar to what happens in REM sleep but occurs when the individual is still awake

How is Sleep Regulated?

  • Wakefulness is maintained by systems in the upper brainstem and hypothalamus

    • Neurons here use acetylcholine, norepinephrine, serotonin, glutamate to connect with the forebrain

    • Neurons in the hypothalamus use orexin and some contain histamine

    • Thalamus and basal forebrain activation by acetylcholine is very important too

      • basal means “closest to midbrain/base”

  • Level of alertness can be shown in an activated low-volt EEG

  • Arousing systems are less active in non-REM sleep

    • Transmission of information to the thalamus is limited

  • Ventrolateral preoptic (VLPO) nucleus: area in the brain that causes suppression of arousal systems

    • VLPO nucleus neurons have the inhibitors galanin and GABA

    • Damage to the VLPO area produces irreversible insomnia

  • In REM sleep, there is an internally activated brain and EEG but the external input is suppressed

    • Internal activation comes from cyclically active REM sleep generator neurons in the brainstem

  • Signals from neurons cause the excitation of the forebrain

    • Leads to rapid eye movements & muscle suppression

  • Forebrain excitation driving force behind dreams of REM sleep

  • Motor cortex neurons fire as rapidly during REM sleep as during waking movement

    • Explains movement coinciding with dreams

  • Periodic recurrence of REM sleep

    • REM sleep occurs every 90 min during sleep

    • This is caused by on-and-off switching of REM-generators (acetylcholine, glutamate) and REM-suppressors (norepinephrine, serotonin, GABA)

The Sleep-Wakefulness Cycle

  • 2 determining factors for sleepiness:

    • Circadian system: Monitoring the time of day/night

    • Homeostatic system: monitoring how long the person is awake

  • Circadian system is regulated by the suprachiasmatic nucleus

    • Suprachiasmatic nucleus: a small group of cells in the hypothalamus serving as the master clock

      • It expresses clock proteins that go through a biochemical cycle of approximately 24 hrs

      • This sets the pace for daily cycles of activity, sleep hormone release, etc.

  • The suprachiasmatic nucleus also receives input from the retina

    • The clock can be reset by light so it is linked to the outside day-night cycle

  • Also provides information to the subparaventricular nucleus → dorsomedial nucleus → VLPO and orexin neurons

    • Orexin: an excitatory signal to arousal system especially norepinephrine neurons

      • Orexin activation plays role in preventing transitions into REM sleep during the day

  • Arousal mediated by orexin and activation of norepinephrine neurons in the locus coeruleus

    • Locus coeruleus: a lateral part of brain stem that has norepinephrine producing neurons that mediate arousal along with orexin

  • The homeostatic system responds to longer wake periods by increasing the urge to sleep

    • The longer a person is awake, the greater the likelihood of an increase in sleep-inducing factors

  • Adenosine: a very important sleep promotor

    • More adenosine means increased sleepiness

    • Adenosine release starts in the basal forebrain and spreads to the rest of the cortex

    • Increased adenosine levels slow down cellular activity and diminish arousal

    • Adenosine levels decrease during sleep

  • Brain adenosine may be produced by ATP breakdown over the course of wakefulness

  • Neuron activity decreases and adenosine levels decline in non-REM sleep

    • ATP levels increase during sleep