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.