Chapter 9 wakefulness and sleep
This presentation is the property of its rightful owner.
Sponsored Links
1 / 71

Chapter 9 Wakefulness and Sleep PowerPoint PPT Presentation


  • 133 Views
  • Uploaded on
  • Presentation posted in: General

Chapter 9 Wakefulness and Sleep. Rhythms of Waking and Sleep. Some animals generate endogenous circannual rhythms, internal mechanisms that operate on an annual or yearly cycle. Example: Birds migratory patterns, animals storing food for the winter. Rhythms of Waking and Sleep.

Download Presentation

Chapter 9 Wakefulness and Sleep

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Chapter 9Wakefulness and Sleep


Rhythms of Waking and Sleep

  • Some animals generate endogenous circannual rhythms, internal mechanisms that operate on an annual or yearly cycle.

    • Example: Birds migratory patterns, animals storing food for the winter.


Rhythms of Waking and Sleep

  • All animals produce endogenous circadian rhythms, internal mechanisms that operate on an approximately 24 hour cycle.

  • Animals generate endogenous 24 hour cycles of wakefulness and sleep.

    • Also regulates the frequency of eating and drinking, body temperature, secretion of hormones, urination, and sensitivity to drugs.


Rhythms of Waking and Sleep

  • Can differ between people and lead to different patterns of wakefulness and alertness.

  • Change as a function of age.

    • Example: sleep patterns from childhood to late adulthood.


Rhythms of Waking and Sleep

  • The purpose of the circadian rhythm is to keep our internal workings in phase with the outside world.

  • Human circadian clock generates a rhythm slightly longer than 24 hours when it has no external cue to set it.

  • Resetting our circadian rhythms is sometimes necessary.


Rhythms of Waking and Sleep

  • Free-running rhythm is a rhythm that occurs when no stimuli resets it.

  • A zeitgeber is a term used to describe any stimulus that resets the circadian rhythms.

  • Light is the primary one.

  • Exercise, noise, meals, and temperature are others zeitgebers.


Rhythms of Waking and Sleep

  • Jet lag refers to the disruption of the circadian rhythms due to crossing time zones.

    • Stems from a mismatch of the internal circadian clock and external time.

  • Characterized by sleepiness during the day, sleeplessness at night, and impaired concentration.

  • Traveling west “phase-delays” our circadian rhythms.

  • Traveling east “phase-advances” our circadian rhythms.


Rhythms of Waking and Sleep

  • Circadian rhythms remain consistent despite lack of environmental cues indicating the time of day

  • Most people can adjust to 23- or 25- hour day but not to a 22- or 28- hour day.

  • People who engage in shift work often fail to adjust completely.


Rhythms of Waking and Sleep

  • Mechanisms of the circadian rhythms include the following:

    • The Suprachiasmatic nucleus

    • Genes that produce certain proteins

    • Melatonin levels


Rhythms of Waking and Sleep

  • The suprachiasmatic nucleus (SCN) is part of the hypothalamus and the main control center of the circadian rhythms of sleep and temperature.

    • Located above the optic chiasm.

    • Damage to the SCN results in less consistent body rhythms that are no longer synchronized to environmental patterns of light and dark.


Rhythms of Waking and Sleep

  • The SCN generates circadian rhythms in a genetically controlled, unlearned manner.

  • Single cell extracted from the SCN and raised in tissue culture continues to produce action potential in a rhythmic pattern.

  • Various cells communicate with each other to sharpen the circadian rhythm.


Rhythms of Waking and Sleep

  • Light resets the SCN via a small branch of the optic nerve known as the retinohypothalamic path.

    • Travels directly from the retina to the SCN.

  • The retinohypothalamic path comes from a special population of ganglion cells that have their own photopigment called melanopsin.

    • The cells respond directly to light and do not require any input from the rods or cones.


Rhythms of Waking and Sleep

  • Two types of genes are responsible for generating the circadian rhythm.

    • Period - produce proteins called Per.

    • Timeless - produce proteins called Tim.

  • Per and Tim proteins increase the activity of certain kinds of neurons in the SCN that regulate sleep and waking.

  • Mutations in the Per gene result in odd circadian rhythms.


Rhythms of Waking and Sleep

  • The SCN regulates waking and sleeping by controlling activity levels in other areas of the brain.

  • The SCN regulates the pineal gland, an endocrine gland located posterior to the thalamus.

  • The pineal gland secretes melatonin, a hormone that increases sleepiness.


Rhythms of Waking and Sleep

  • Melatonin secretion usually begins 2 to 3 hours before bedtime.

  • Melatonin feeds back to reset the biological clock through its effects on receptors in the SCN.

  • Melatonin taken in the afternoon can phase-advance the internal clock and can be used as a sleep aid.


Stages of Sleep And Brain Mechanisms

  • Sleep is a state that the brain actively produces.

  • Characterized by a moderate decrease in brain activity and decreased response to stimuli.

  • Sleep differs from the following states:

    • Coma

    • Vegetative state

    • Minimally conscious state

    • Brain death


Stages of Sleep And Brain Mechanisms

  • Coma – extended period of unconsciousness caused by head trauma, stroke, or disease characterized by low brain activity that remains fairly steady

    • Person shows little response to stimuli

  • Vegetative state – person alternates between periods of sleep and moderate arousal but no awareness of surrounding

    • Some autonomic arousal to painful stimulus

    • No purposeful activity/ response to speech


Stages of Sleep And Brain Mechanisms

  • Minimally conscious state - one stage higher than a vegetative state marked by occasional brief periods of purposeful action and limited speech comprehension

  • Brain death - no sign of brain activity and no response to any stimulus


Stages of Sleep And Brain Mechanisms

  • The electroencephalograph (EEG) allowed researchers to discover that there are various stages of sleep.

  • Allows researchers to compare brain activity at different times during sleep.

  • A polysomnograph is a combination of EEG and eye-movement records


Stages of Sleep And Brain Mechanisms

  • Alpha waves are present when one begins a state of relaxation.

  • Stage 1 sleep is when sleep has just begun.

    • the EEG is dominated by irregular, jagged, low voltage waves.

    • brain activity begins to decline.


Stages of Sleep And Brain Mechanisms

  • Stage 2 sleep is characterized by the presence of:

    • Sleep spindles - 12- to 14-Hz waves during a burst that lasts at least half a second.

    • K-complex - a sharp high-amplitude negative wave followed by a smaller, slower positive wave.


Stages of Sleep And Brain Mechanisms

  • Stage 3 and stage 4 together constitute slow wave sleep (SWS) and is characterized by:

    • EEG recording of slow, large amplitude wave.

    • Slowing of heart rate, breathing rate, and brain activity.

    • Highly synchronized neuronal activity.


Stages of Sleep And Brain Mechanisms

  • Rapid eye movement sleep (REM) are periods characterized by rapid eye movements during sleep.

  • Also know as paradoxical sleep is deep sleep in some ways, but light sleep in other ways.

  • EEG waves are irregular, low-voltage and fast.

  • Postural muscles of the body are more relaxed than other stages.


Stages of Sleep And Brain Mechanisms

  • Stages other than REM are referred to as non-REM sleep (NREM).

  • When one falls asleep, they progress through stages 1, 2, 3, and 4 in sequential order.

  • After about an hour, the person begins to cycle back through the stages from stage 4 to stages 3 and 2 and than REM.

  • The sequence repeats with each cycle lasting approximately 90 minutes.


Stages of Sleep And Brain Mechanisms

  • Stage 3 and 4 sleep predominate early in the night.

    • The length of stages 3 and 4 decrease as the night progresses.

  • REM sleep is predominant later in the night.

    • Length of the REM stages increases as the night progresses.

  • REM is strongly associated with dreaming, but people also report dreaming in other stages of sleep.


Stages of Sleep And Brain Mechanisms

  • Various brain mechanisms are associated with wakefulness and arousal.

  • The reticular formation is a part of the midbrain that extends from the medulla to the forebrain and is responsible for arousal.


Stages of Sleep And Brain Mechanisms

  • The pontomesencephalon is a part of the midbrain that contributes to cortical arousal.

    • Axons extend to the thalamus and basal forebrain which release acetylcholine and glutamate

    • produce excitatory effects to widespread areas of the cortex.

  • Stimulation of the pontomesencephalon awakens sleeping individuals and increases alertness in those already awake.


Stages of Sleep And Brain Mechanisms

  • The locus coeruleus is small structure in the pons whose axons release norepinephrine to arouse various areas of the cortex and increase wakefulness.

    • Usually dormant while asleep.


Stages of Sleep And Brain Mechanisms

  • The basal forebrain is an area anterior and dorsal to the hypothalamus containing cells that extend throughout the thalamus and cerebral cortex.

  • Cells of the basal forebrain release the inhibitory neurotransmitter GABA.

  • Inhibition provided by GABA is essential for sleep.

  • Other axons from the basal forebrain release acetylcholine which is excitatory and increases arousal.


Stages of Sleep And Brain Mechanisms

  • The hypothalamus contains neurons that release “histamine” to produce widespread excitatory effects throughout the brain.

    • Anti-histamines produce sleepiness.


Stages of Sleep And Brain Mechanisms

  • Orexin is a peptide neurotransmitter released in a pathway from the lateral nucleus of the hypothalamus highly responsible for the ability to stay awake.

    • Stimulates acetylcholine-releasing cells in the basal forebrain to stimulate neurons responsible for wakefulness and arousal.

    • The basal forebrain is an area just anterior and dorsal to the hypothalamus


Stages of Sleep And Brain Mechanisms

  • Functions of the inhibitory neurotransmitter GABA are also important:

    • Decreasing the temperature and metabolic rate

    • Decreasing stimulation of neurons.


Stages of Sleep And Brain Mechanisms

  • During REM sleep:

    • Activity increases in the pons (triggers on set of REM sleep) and limbic system (emotional systems), parietal cortex and temporal cortex.

    • Activity in the pons triggers onset of REM sleep

    • Activity decreases in the primary visual cortex, the motor cortex, and the dorsolateral prefrontal cortex.


Stages of Sleep And Brain Mechanisms

  • REM sleep is also associated with a distinctive pattern of high-amplitude electrical potentials known as PGO waves.

  • Waves of neural activity are detected first in the pons and then in the lateral geniculate of the hypothalamus, and then the occipital cortex.

  • REM deprivation results in high density of PGO waves when allowed to sleep normally.


Stages of Sleep And Brain Mechanisms

  • Cells in the pons send messages to the spinal cord which inhibit motor neurons that control the body’s large muscles.

    • Prevents motor movement during REM sleep.

  • REM is also regulated by serotonin and acetylcholine.

    • Drugs that stimulate Ach receptors quickly move people to REM.

    • Serotonin interrupts REM.


Stages of Sleep And Brain Mechanisms

  • Insomnia is a sleep disorder associated with inadequate sleep.

    • Caused by a number of factors including noise, stress, pain medication.

    • Can also be the result of disorders such as epilepsy, Parkinson’s disease, depression, anxiety or other psychiatric conditions.

    • Dependence on sleeping pills and shifts in the circadian rhythms can also result in insomnia.


Stages of Sleep And Brain Mechanisms

  • Sleep apnea is a sleep disorder characterized by the inability to breathe while sleeping for a prolonged period of time.

  • Consequences include sleepiness during the day, impaired attention, depression, and sometimes heart problems.

  • Cognitive impairment may result from loss of neurons due to insufficient oxygen levels.

  • Causes include, genetics, hormones, old age, and deterioration of the brain mechanisms that control breathing and obesity.


Stages of Sleep And Brain Mechanisms

  • Narcolepsy is a sleep disorder characterized by frequent periods of sleepiness.

  • Four main symptoms include:

    • Gradual or sudden attack of sleepiness.

    • Occasional cataplexy - muscle weakness triggered by strong emotions.

    • Sleep paralysis- inability to move while asleep or waking up.

    • Hypnagogic hallucinations- dreamlike experiences the person has difficulty distinguishing from reality.


Stages of Sleep And Brain Mechanisms

(Insomnia cont’d)

  • Seems to run in families although no gene has been identified.

  • Caused by lack of hypothalamic cells that produce and release orexin.

  • Primary treatment is with stimulant drugs which increase wakefulness by enhancing dopamine and norepinephrine activity.


Stages of Sleep And Brain Mechanisms

  • Periodic limb movement disorder is the repeated involuntary movement of the legs and arms while sleeping.

    • Legs kick once every 20 to 30 seconds for periods of minutes to hours.

    • Usually occurs during NREM sleep.


Stages of Sleep And Brain Mechanisms

  • REM behavior disorder is associated with vigorous movement during REM sleep.

    • Usually associated with acting out dreams.

    • Occurs mostly in the elderly and in older men with brain diseases such as Parkinson’s.

    • Associated with damage to the pons (inhibit the spinal neurons that control large muscle movements).


Stages of Sleep And Brain Mechanisms

  • Night terrors are experiences of intense anxiety from which a person awakens screaming in terror.

    • Usually occurs in NREM sleep.

  • “Sleep talking” occurs during both REM and NREM sleep.

  • “Sleepwalking” runs in families, mostly occurs in young children, and occurs mostly in stage 3 or 4 sleep.


Why Sleep? Why REM? Why Dreams?

  • Functions of sleep include:

    • Energy conservation.

    • Restoration of the brain and body.

    • Memory consolidation.


Why Sleep? Why REM? Why Dreams?

  • The original function of sleep was to probably conserve energy.

  • Conservation of energy is accomplished via:

    • Decrease in body temperature of about 1-2 Celsius degrees in mammals.

    • Decrease in muscle activity.


Why Sleep? Why REM? Why Dreams?

  • Animals also increase their sleep time during food shortages.

    • sleep is analogous to the hibernation of animals.

  • Animals sleep habits and are influenced by particular aspects of their life including:

    • how many hours they spend each day devoted to looking for food.

    • Safety from predators while they sleep

      • Examples: Sleep patterns of dolphins, migratory birds, and swifts.


Why Sleep? Why REM? Why Dreams?

  • Sleep enables restorative processes:

    • Proteins rebuilt in the brain

    • Energy supplies replenished

  • Moderate sleep deprivation results in impaired concentration, irritability, hallucinations, tremors, unpleasant mood, and decreased immune system functioning.

  • Caffeine increases arousal by blocking the receptors for adenosine (accumulate during wakefulness and increase drowsiness)


Why Sleep? Why REM? Why Dreams?

  • Sleep also plays an important role in enhancing learning and strengthening memory.

    • Performance on a newly learned task is often better the next day if adequate sleep is achieved during the night.

  • Increased brain activity occurs in the area of the brain activated by a newly learned task while one is asleep.

    • Activity also correlates with improvement in activity seen the following day.


Why Sleep? Why REM? Why Dreams?

  • Humans spend one-third of their life asleep.

  • One-fifth of sleep time is spent in REM.

  • Species vary in amount of sleep time spent in REM.

    • Percentage of REM sleep is positively correlated with the total amount of sleep in most animals.

  • Among humans, those who get the most sleep have the highest percentage of REM.


Why Sleep? Why REM? Why Dreams?

  • Research is inconclusive regarding the exact functions of REM.

  • During REM:

    • The brain may discard useless connections

    • Learned motor skills may be consolidated.

  • Maurice (1998) suggests the function of REM is simply to shake the eyeballs back and forth to provide sufficient oxygen to the corneas.


Why Sleep? Why REM? Why Dreams?

  • Biological research on dreaming is complicated by the fact that subjects can not often accurately remember what was dreamt.

  • Two biological theories of dreaming include:

    • The activation-synthesis hypothesis.

    • The clinico-anatomical hypothesis.


Why Sleep? Why REM? Why Dreams?

  • The activation-synthesis hypothesis suggests dreams begin with spontaneous activity in the pons which activates many parts of the cortex.

    • The cortex synthesizes a story from the pattern of activation.

    • Normal sensory information cannot compete with the self-generated stimulation and hallucinations result.


Why Sleep? Why REM? Why Dreams?

  • Input from the pons activates the amygdala giving the dream an emotional content.

  • Because much of the prefrontal cortex is inactive during PGO waves, memory of dreams is weak.

    • Also explains sudden scene changes that occur in dreams.


Why Sleep? Why REM? Why Dreams?

  • The clinico-anatomical hypothesis places less emphasis on the pons, PGO waves, or even REM sleep.

    • Suggests that dreams are similar to thinking, just under unusual circumstances.

  • Similar to the activation synthesis hypothesis in that dreams begin with arousing stimuli that are generated within the brain.

    • Stimulation is combined with recent memories and any information the brain is receiving from the senses.


Why Sleep? Why REM? Why Dreams?

  • Since the brain is getting little information from the sense organs, images are generated without constraints or interference.

  • Arousal can not lead to action as the primary motor cortex and the motor neurons of the spinal cord are suppressed.

  • Activity in the prefrontal cortex is suppressed which impairs working memory during dreaming.


Why Sleep? Why REM? Why Dreams?

  • Activity is high in the inferior part of the parietal cortex, an area important for visual-spatial perception.

    • Patients with damage report problems with binding body sensations with vision and have no dreams.

    • Activity is also high in areas outside of V1, accounting for the visual imagery of dreams.


Why Sleep? Why REM? Why Dreams?

  • Activity is high in the hypothalamus and amygdala which accounts for the emotional and motivational content of dreams.

  • Either internal or external stimulation activates parts of the parietal, occipital, and temporal cortex.

  • Lack of sensory input from V1 and no criticism from the prefrontal cortex creates the hallucinatory perceptions.


  • Login