Chapter 11 - Sleep and Waking Flashcards
BIORHYTHMS
Seasonal migrations, mating seasons, and the human menstrual cycle are just a few examples of behaviors that occur at regular intervals in response to internal BIORHYTHMS.
The interplay of sleep and waking cycles follow CIRCADIAN rhythms - circadian means “about a day”. Furthermore, cycle of alertness and quiet - called ULTRADIAN rhythms - occur about every 90 to 120 minutes.
To establish and maintain these rhythms, internal biological clocks interact with stimuli known as ZEITGEBERS - of which, for human beings, light is the most important one.
In absence of light - as it is the case with totally blind people - human FREE RUNNING CIRCADIAN rhythms last approxImately 24.2 hours to 24.9 hours. Exposure to light ENTRAINS - resets - the normal 24 hour cycle.
INDIVIDUAL VARIATION in SLEEP PATTERNS
LARKS are individuals who are most alert and productive in the morning, whereas night people have been referred to as “NIGHT OWLS”. Nearly everyone acts like an owl during adolescence, probably because of a dramatic drop of MELATONIN at the onset of puberty.
SHIFT MALADAPTATION SYNDROME
SHIFT MALADAPTATION SYNDROME is a condition that typically affects night workers - it is caused by disruption of typical sleep patterns, or the conflict between internal clocks and external zeitgebers. It results in health, personality, mood and interpersonal problems.
JET LAG
JET LAG is the experience of fatigue, irritability and sleepiness resulting from travel across time zones - it results from conflict between internal clocks and external zeitgebers. Not all changes in time zone have equal effects:
1) WESTWARD travel causes minor symptoms;
2) EASTWARD travel causes the major symptoms, for it is harder to adjust to a phase-advance of our biorhythm than to a phase-delay.
Symptoms similar to those of jet lag are experienced the day after the spring shift of DAYLIGHT SAVING TIME.
the SUPRACHIASMATIC NUCLEUS (SCN)
The SUPRACHIASMATIC NUCLEUS (SCN) of the HYPOTHALAMUS, located above the OPTIC CHIASM, is the body’s internal master clock. Input to the SCN comes from axons of special ganglion cells which leave the optic nerve and project to the SCN, forming the RETINOHYPOTHALAMIC PATHWAY. Unlike other retinal cells, these cells do not process visual information, yet they contain a pigment known as MELANOPSIN.
The SCN - which is active only during the day - modulates the release of the hormone MELATONIN from the PINEAL GLAND into the CSF. Melatonin is a neurochemical that modulates brainstem structures related to waking and sleep - its production is suppressed by light.
The SCN also modulates hormone release of the PITUITARY GLAND - such as growth hormone release - and manages other sleep-related changes, such as body temperature, production of urine, and blood pressure changes.
ALERTNESS, TEMPERATURE and HORMONE SECRETIONS in the circadian cycle
ALERTNESS, TEMPERATURE and HORMONES SECRETIONS fluctuate with patterns of waking and sleeping.
1) MELATONIN are very low during the day, begin to rise in the hours before sleep, and usually peak at about 4 AM;
2) CORTISOL levels are normally high early in the morning and lower at night. Higher levels of cortisol are associated with higher blood pressure, higher heart rate, and the mobilization of the body’s energy stores - it is the hormone released during times of stress.
3) GROWTH HORMONE is released primarily at night during the deepest sleep stages;
4) BODY TEMPERATURE and ALERTNESS peak in the middle of the day and decrease during sleep - they are positively correlated.
PER, TIM, and CLOCK
At the cellular level, three genes and the fluctuations of their protein products are responsible for circadian rhythms: PER, TIM, and CLOCK. Together, per and tim proteins inhibit the Clock protein, whereas the Clock protein promotes the production of more per and tim proteins. As levels of per and tim proteins increase, inhibition of the Clock protein ensures that no further per and tim proteins will be produced. When levels of per and tim proteins drop over time, the reduced inhibition of the Clock protein results in increased production of per and tim proteins.
SEASONAL AFFECTIVE DISORDER (SAD) - MAJOR DEPRESSIVE DISORDER (MDD) with SEASONAL PATTERNS
During the winter months at higher latitudes - areas closer to the poles of the earth, - the reduction in daylight hours can interfere with circadian rhythms and thus lead to MDD with seasonal patterns.
Two mechanisms seem to be responsible for this disorder:
1) The drop of SEROTONIN levels during winter, caused by overabundance of serotonin transporters that clear up the synaptic gap. Serotonin not only serves as a precursor for melatonin synthesis in the pineal gland, but its own synthesis is activated by light.
2) disruptions in melatonin release caused by uneven patterns of daily light.
Seasonal depression is treated by exposure to bright lights - or LIGHT THERAPY - with reduces the number of serotonin transporters.
EEG RECORDINGS of waking and sleep
We can evaluate waking and sleep using EEG recordings - DESYNCHRONOUS brain activity is correlated with ALERTNESS, whereas SYNCHRONOUS activity characterizes deep stages of sleep.
1) During WAKING, EEG recordings typically alternate between BETA waves - associated with active information processing - and ALPHA waves - associated with relaxation and drowsiness. Alpha and beta wave patterns - and related alertness levels - follow ULTRADIAN cycles of 90 to 120 min.
2) In the brief stage 1 NREM, EEG recordings show some THETA wave activity. Rate and muscle tension decrease, and people often experience MYOCLONIA, muscle jerks associated with brief visual images which usually disrupt sleep.
3) In stage 2 NREM, which accounts for 50% of the night’s entire sleep, EEG recordings show THETA wave activity interrupted by SLEEP SPINDLES and K-COMPLEXES, short bursts of brain activity. Sleep spindles are caused by interactions between the thalamus and the cortex, whereas K-complex are responses to external unexpected stimuli.
They might reflect the brain’s efforts to keep us asleep while continuing to monitor the external environment.
4) In stages 3 NREM and 4 NREM, EEG recordings show DELTA wave activity. Body temperature, breathing, blood pressure, and heart rate are at very low levels due to the activity of the PNS, and awakening is difficult and disorienting. The only difference between the two stages is that stage 4 consist of significantly more delta wave activity.
5) In REM (rapid eye movement) sleep, the EEG shows activity very similar to beta activity observed during waking - neural activity is DESYNCHRONOUS, giving this stage the name of paradoxical sleep. The SNS is activated and heart rate, blood pressure, and breathing become rapid or irregular - major postural muscles are completely inactive, effectively paralyzing the sleeper.
REM stages follow ultradian cycles of 90 to 120 minutes, and a typical sleeper experiences 5 REM periods per night. Stages 3 and 4 are especially dominant in the first half of the sleep cycle, whereas REM is the principal stage seen in hours 5 through 8.
BRAIN NETWORKS of WAKING and SLEEP
Circuits connecting the BRAINSTEM, HYPOTHALAMUS, and BASAL FOREBRAIN play essential roles in the initiation and maintenance of stages of waking and sleep.
1) During WAKING, only the PONS is INACTIVE;
2) During NREM sleep, only the PREOPTIC AREA of the HYPOTHALAMUS is ACTIVE;
3) During REM sleep, only the PONS is ACTIVE:
Areas of the PONS are responsible for several distinctive features of REM sleep, including muscular paralysis and rapid eye movements. Each eye movement is accompanied by a waveform known as a PGO WAVE. These waveforms originate in the pons (P), travel to the GENICULATE NUCLEUS of the THALAMUS (G), and reach the primary visual cortex in the OCCIPITAL LOBE (O). Rapid eye movements are correlated with vivid dreaming, suggesting a connection with dream imagery.
CHANGES in sleep over the LIFETIME
CHANGES in sleep in quantity and quality - diverse sleep stage patterns - take place over the LIFETIME. Overall, time spent awake steadily increase, and subsequent reduction of both REM and NREM sleep take place.
- Newborn infants spend as much 16 hours per day in sleep, and about half of their sleeping time is spent in REM sleep.
- By the age of one year, the child’s sleep time has been reduced to 13 hours per day.
- Puberty is characterised with a substantial decrease of time spent in REM and stages 3 and 4 sleep;
- Around the age of 50, sleep time - especially time spent in deep sleep -continues to decrease until a person’s eighties. Increased awakening accompanies a reduction in sleep spindles - which are responsible for sleep maintenance.
ADVANTAGES of SLEEP
Sleep has 3 main functions:
1) It keeps us SAFE:
Sleep prevents animals from being active during parts of the day when they are least safe from predators.
We can predict the amount of time an animal will sleep on the basis of its risk of being attacked by other animals. For example, the horse is a heavily preyed upon animal in the wild, and it sleep as little as one to two hours per day - Predators, such as lions, tend to sleep whenever they desire for lengthy periods of time.
2) It RESTORES OUR BODIES (NREM sleep):
Sleep - particularly NREM sleep - helps us restore our bodies and conserve energy. Metabolism rates are positively correlated with the production of FREE RADICALS, whose damage to tissue is repaired in NREM sleep - low temperature and metabolism rates provide an ideal environment. Deprivation of stages 3 and 4 sleep causes muscle and joint pain.
Most GROWTH HORMONE - responsible of building muscle and bone mass and maintaining immune system function - is released during stages 3 and 4 NREM.
3) It consolidates MEMORY and regulates EMOTION:
Learning during waking might be a simple matter of strengthening connections, whereas sleep-related memory processes might involve the REORGANIZATION of existing MEMORY SYSTEMS to accommodate new information. REM sleep improves the retention of highly EMOTIONAL material, whereas NREM sleep improves the retention of PROCEDURAL memory. Sleep has also been shown to play an important role in a person’s ability to identify an emotion as inappropriate and choose and implement an appropriate response.
SPECIAL CHARACTERISTICS of REM SLEEP include:
1) MEMORY CONSOLIDATION - REM sleep increases after substantial learning. REM sleep influences the elimination and maintenance of newly formed synapses, playing a role in the reorganization of memory systems.
2) BRAIN DEVELOPMENT - the large proportion of REM sleep observed in young children correlates with periods of time in which the brain is undergoing great changes.
3) REM REBOUND - after REM deprivation, the organism tries to make up for lost REM sleep by entering REM stages more frequently.
WHAT we DREAM
Dreaming behavior occurs during both REM sleep and NREM:
1) REM dreams are lengthy, complicated, vivid, and story-like. They are often recalled upon awakening;
2) NREM dreams are are short episodes characterized by logical single images and a relative lack of emotion. They usually are forgotten unless full awakening.
70 % of our dreams have negative emotional content:
1) NIGHTMARES are vivid negative dreams that occur during REM sleep, and people who experience them are usually scared and upset upon awakening. They occur late in the sleep cycle - when REM stages are longer - and often prevent immediate return to sleep.
2) NIGHT TERRORS are negative dreams that occur during NREM sleep, and people who experience them are disoriented, confused and do not appear to be comforted by caregivers. They usually occur in the first half of the sleep cycle and do not prevent quick return to sleep, making them harder to remember in the morning.
LUCID DREAMING is a phenomenon in which the dreamer is consciously aware that he or she is dreaming and uses this awareness to control or direct the content of the dream. Lucid dreamers have been used in research to estimate the duration of events occurring during dream.
THEORIES on the FUNCTIONS of DREAMING
Three main theories have been advance to explain the possible functions of dreaming:
1) The ACTIVATION-SYNTHESIS THEORY maintains that dreams reflects nothing more than ongoing NEURAL ACTIVITY. According to this view, the forebrain tries to make sense of the random activation of memories and associations caused by PGO impulses in the cortex. Scholars supporting this view argue that:
A) Sleeping participants reporting dreaming of rain when sprinkled with water;
B) Dreams of being unable to move might reflect muscle paralysis occurring in REM sleep;
C) Erotic dreams might reflect sexual arousal experienced during REM sleep;
D) Dreams of flying or falling might reflect unusual activation of the vestibular system.
2) The THREAT SIMULATION HYPOTHESIS is an EVOLUTIONARY MODEL that suggest that animals evolved the ability to dream to simulate danger and practice escape strategies.
3) Another theory suggests that the elimination and maintenance of newly formed SYNAPSES that take place in REM sleep help organisms forget irrelevant and unnecessary information. Thus, dreams would be the experience of the reorganisation of MEMORY SYSTEMS.
SLEEP DISORDERS
SLEEP DISORDERS can be divided in:
A) DYSSOMNIAS, or difficulties in the initiation, maintenance, timing, and quality of sleep. Dyssomnias include:
1) INSOMNIA;
2) NARCOLEPSY, CATAPLEXY, and SLEEP PARALYSIS;
3) SLEEP APNEA.
B) PARASOMNIAS, or unusual behaviors disturb ongoing sleep. Parasomnias include:
1) SUDDEN INFANT DEATH SYNDROME (SIDS);
2) SLEEP TALKING;
3) SOMNAMBULISM (sleepwalking);
4) REM SLEEP BEHAVIOUR DISORDER;
5) ENURESIS;
6) RESTLESS LEG SYNDROME.
