Chapter 8 PDF - Wakefulness and Sleep

Chapter 8 Type textbook Tags BIOPSYCH Due Date @December 9, 2024 Status Done Wakefulness and sleep Module 8.1 Rhythms of waking and sleeping endogenous (generated from with...

Chapter 8 Type textbook Tags BIOPSYCH Due Date @December 9, 2024 Status Done Wakefulness and sleep Module 8.1 Rhythms of waking and sleeping endogenous (generated from within) rhythms endogenous circannual rhythm : innate rhythms for seasonal changes endogenous circadian rhythms : innate rhythm that lasts approximately a day posterior areas of the cerebral cortex, activity correlates mainly with your circadian rhythm, and only secondarily with how long you have been awake have circadian rhythms in our hunger, thirst, liver activity, insulin secretion, intestinal activity, DNA repair setting and resetting the biological clock zeitgeber : stimulus that resets your circadian rhythm light is by far the dominant zeitgeber for land animals (also exercise, arousal, meals, temperature of the environement) tides are important for some marine animals blind people set their circadian rhythms by noise, temperature, meals and activity jet lag disruption of circadian rhythms after crossing time zones going west, we phase delay our circadian rhythms going east, we phase advance to sleep earlier and awaken earlier Chapter 8 1  prolonged elevation of cortisol damages the neurons in the hippocampus night work people adjust better if they sleep in a very dark room during the day and work under very bright lights at night short-wavelength light resets the circadian rhythm more strongly than long- wavelength light morning people and evening people morning people or “larks” : awaken early, reach their peak of productivity early, and become less alert later more impaired when working the night shift often report more happiness (work schedule more in line with circadian rhythm) evening people or “owls” : warm up slowly, both literally and figuratively, reaching their peak in the late afternoon or evening most impaired when working the morning shift score lower in school, more prone to some risk-behaviours depends on age: children go to bed early adolescents start staying/waking up later (until 20); might be result of sex hormones -> then the rhythm gradually reverses can also depend on genetics and environment e.g. living In a big city with bight lights at night -> staying up later mechanisms of the biological clock brain generates its own rhythms remains steady despite food or water deprivation, X-rays, tranquilizers, alcohol, anesthesia, lack of oxygen, most kinds of brain damage, or the removal of endocrine organs the suprachiasmatic nucleus (SCN) Chapter 8 2  part of the hypothalamus just above (”supra”) the optic chiasm generates circadaian rhthms automatically if SCN neurons are disconnected from the rest of the brain or removed from the body and maintained in tissue culture, they continue to produce a circadian rhythm of action potentials interactions among neurons and astrocytes sharpen the accuracy of the rhythm how light resets the SCN a branch of the optic nerve, the retinohypothalamic path, alters the SCN’s settings comes from certain retinal ganglion cells that have their own photopigment, melanpsin the axons comprising that path originate from special ganglion cells that respond to light by themselves, even if they do not receive input from rods or cones these ganglion cells respond mainly to short-wave length (blue) light biochemistry of the circadian rhythm in fruit flies, two genes (PER & TIM) produce two proteins (PER & TIM) —> these proteins concentrations promote sleep/inactivity mRNA levels responsible for production of PER & TIM increase in the morning, but the actual synthesis of the proteins lag hours behind increasing levels of PER and TIM inhibit genes that produce mRNA high levels of PER & TIM at night; decrease of mRNA at morning both levels are low again (feedback circle takes 24 hours) melatonin the pineal gland releases the hormone melatonin released mostly at night — increases sleepiness Chapter 8 3  also helpts control the onset of puberty and adjustments to changes of season, such as hibernation melatonin secretions starts to increase about 2 or 3 hours before bedtime taking melatonin earlier (not right before sleep) can hasten the onset of sleepiness and shift the circadian rhythm Module 8.2 Stages of sleep and brain mechanisms sleep and other interruptions and consciousness coma is an extended period of unconsciousness caused by head trauma, stroke and disease unresponsive wakefulness syndrome : alternates between sleep and moderate arousal. even during the more aroused state, the person shows no awareness of surroundings and no purposeful behaviour breathing is more regular, and a painful stimulus increases heart rate, breathing and sweating eye movements occur, but they do not follow a target might laugh or cry, but not in response to external event minimally conscious state : brief periods of purposeful actions and a limited amount of speech comprehension can last for months or years brain death : condition with no sign of brain activity and no response to any stimulus stages of sleep polysomnograph : combination of EEG and eye-movement records a. relaxed, awake : steady series of alpha waves at a frequency of 8 to 12 per second b. stage 1 sleep : irrregular, jagged, low-voltage waves c. stage 2: sleep spindles and K-complexes K-complex: a sharp wave associated with temporary inhibition of neuronal firing Chapter 8 4  sleep spindles: consists of 12-to 14-Hz waves that last a least half a second; they result from oscillating interactions between cells in thalamus and cortex increase in number after learning -> correlates positively with memory improvement & nonverbal tests of IQ d. slow-wave sleep (SWS): heart rate, breathing rate, and brain activity decrease, whereas slow, large-amplitude waves become more common = stages 3 & 4 -> differ in the prevalence of slow waves (3 fewer; 4 more) slow waves indicate highly synchronized neural activity; since input to the cerebral cortex is greatly inhibited EEG shows bigger, slower waves than in wakefulness/stage 1 (where neurons out of phase through cortex activity produce short, rapid, choppy waves) e. stage 5: REM sleep paradoxical or REM sleep periods of eye movements occur during sleep (rapid eye movement (REM) sleep) EEG shows irregular, low-voltage fast waves that indicate increased neuronal activity cells in the pons and medulla inhibit movement of the postural muscles heart rate, blood pressure, breathing rate, and facial twitches fluctuate the stages other than REM are known as non-REM (NREM) sleep brain mechanisms of wakefulness, arousal and sleep brain structures of arousal and attention a cut through the midbrain decreases arousal by damaging the reticular formation : structure that extends from the medulla into the forebrain pontomesencephalon : part of the reticular formation; contributes to cortical arousal; receives input from many sensory systems some axons reach into forebrain & release GABA (inhibiting behaviour; promoting slow-wave sleep) Chapter 8 5  some axons release neurotransmitters that arouse hypothalamus, thalamus & basal forebrain locus coeruleus : small structure in the pons, usually inactive, but it emits bursts of impulses in respond to meaningful, memorable events, especially those that produce autonomic arousal or stress these axons release norepinephrine widely throughout the cortex increases the activity of the most active neurons and decreases the activity of less active neurons, enhancing attention to important information hypothalamus : has both neurons that promote wakefulness and neurons that promote sleep one axon pathway from the hypothalamus releases the excitatory neurotransmitter histamine, which enhances arousal and alertness another pathway from the hypothalamus releases a peptide neurotransmitter called either orexin or hypocretin orexin is important for staying awake relavent to an older person’s problem of waking up in the middle of the night (in the cells that release orexin, the resting potential of the axon rises with aging and gets closer to the threshold for firing. The increased resting potential relates to a change in the potassium channels. As a result, these cells are easily excitable, causing wakefulness) other pathways from the lateral hypothalamus regulate cells in the basal forebrain (area just anterior and dorsal to the hypothalamus) provide axons that extend throughout the thalamus and cerebral cortex. some of them increasing wakefulness and others inhibiting it REM sleep is associated with a distinctive pattern of high-amplitude electrical potentials known as PGO waves (pons-geniculate-occipital) waves of neural activity are detected first in the pons —> lateral geniculate nucleus of thalamus —> occipital cortex stimulus to start REM sleep comes from dopamine release in the amygdala sleep and the inhibition of brain activity Chapter 8 6  neurons in the thalamus become hyperpolarized, decreasing their readiness to respond to stimuli and decreasing the information they transmit to the cortex (though a moderate amount of responsiveness remains) during sleep, axons from the pons and midbrain increase their release of GABA, inhibiting the synaptic spread of information from one neuron to another the release of GABA (inhibitory transmitter) increases because sleep depends on GABA-mediated inhibition, sleep can be local within the brain sleepwalking: asleep in most brain areas; but awake in motor cortex lucid dreaming: dreaming but being aware of being asleep & dreaming -> ability to control dream sleep paralysis: during sleep pons inhibits spinal cord -> no movement; if pons wakes up later than other brain areas -> conscious experience of being paralyzed while being awake sleep disorders average adult humans needs 7.5 to 8.5 hours of sleep per night insomnia : inadequate sleep impairs memory, attention, and cognition magnifies unpleasant emotional reactions and increases the risk of depression causes noise, uncomfortable temperatures, stress, pain, diet and medications can be the result of epilepsy, Parkinson’s, brain tumors, depression, anxiety or other neurological or psy- chiatric conditions, frequent use of sleeping pills sleep apnea : impaired ability to breathe while sleeping breathless periods of a minute or so from which they awaken grasping for breath may not remember their awakenings, although they certainly notice the consequences, such as sleepiness and impaired attention the following day Chapter 8 7  prolonged sleep apnea leads to a loss of neurons, with an impairment of learning and other functions related to obesity, especially middle-aged men have narrower than normal airways and have to compensate by breathing frequently or vigorously narcolepsy : conditioned characterised by periods of sudden sleepiness during the day four main symptoms attacks of sleepiness during the day occasional cataplexy — an attack of muscle weakness while the person remains awake. often triggered by strong emotions, such as anger or great excitement sleep paralysis — an inability to move while falling asleep or waking up hypnagogic hallucinations — dreamlike experiences that the person has trouble distinguishing from reality, often at the onset of sleep cause: lack of the hypothalamic cells that produce and release orexin (important for wakefulness); lack might be caused by an autoimmune reaction most common treatment are stimulant drugs like Ritalin, that enhance dopamine and norepinephrine activity period limb movement disorder: repeated involuntary movement of the legs and sometimes the arms during sleep REM behaviour disorder: moving around vigorously during their REM periods, apparently acting out their dreams inadequate inhibitory transmission (GABA) may be responsible night terrors and sleepwalking: night terrors are experiences of intense anxiety from which a person awakens screaming in terror; they occur during NREM sleep; more common in children Chapter 8 8  sleep walking also more common in children; and more common when sleep deprived or stressed; happens during slow-wave sleep; parts of brain are awake and others sleep it’s not dangerous to waken a sleepwalker; but mostly not helpful either “sexomnia”: sleeping people engage in sexual behaviour (no memory); similar to sleepwalking Module 8.3 Why sleep? why REM? why dreams? functions of sleep resting muscles; decrease metabolism; cellular maintenance; reorganization of synapses; strengthening memories lack of sleep -> dealing worse with stress; lack of attention & performance; … sleep and energy conservation sleep conserves energy during inefficient times, when activity would be wasteful and possibly dangerous analogous to sleep: hibernation low body temperature, heart rate, brain activity, … sleep and memory sleep improves memory and helps reanalyse memories because the hippocampus, which is active while learning, is also active during sleep functions of REM sleep hypothesis: REM is important for strengthening memory another hypothesis: shaking eyes to get enough oxygen to corneas of the eyes biological perspective of dreaming activation-synthesis hypothesis: a dream represents the brain’s effort to make sense of sparse and distorted information beginning with spontaneous activity in the pons that activate some parts of the cortex but not others -> cortex synthesizes spontaneous activity to a Chapter 8 9  story (to make sense of it) e.g. lying flat -> experience of falling e.g. REM-paralysis -> dreaming of being unable to move neurocognitive hypothesis: dreams are regarded as thinking taking place under unusual conditions less sensory information -> more capacity to generate images without constraints Chapter 8 10