sleep and dreaming Flashcards
what is the definition of sleep
readily reversible state of reduced responsiveness to, and interaction with, the environment
sleep is a naturally recurring characterised by reduced or absent consciousness, relatively suspended sensory activity and inactivity of nearly all voluntary muscles
represents an altered state of consciousness
circadian rhythms are the product of both exogenous and endogenous influences - what is the definition of these
endogenous: originate from inside the body, specifically from the central nervous system
exogenous: originate from outside the body (light, temperature, environment)
endogenous rhythms - circannual rhythms
translation - about, year
e.g.birds migratory patterns, animals storing food for winter, hibernation
endogenous rhythms - circadian rhythms
translation - about, day
regulates the frequency of eating and drinking, body temp, secretion of hormones, urination, sensitivity to drugs
purpose is to keep internal workings in phase with the outside world
human circadian clock generates rhythm slightly longer than 24 hours when there are no exogenous cues
what is the name given to a stimulus that resets the circadian rhythm
zeitgeber (time giver)
light is a critical zeitgeber for resetting circadian rhythm
others include;
exercise, meals, temperature of the environment
what are some common disruptions of circadian rhythms
Monday morning blues
daylight savings time in spring
jet lag
shift work
common disruptions of circadian rhythms - jet lag
characterised by sleepiness during the day, sleeplessness during the night
travelling west phase delays our circadian rhythms (late to bed, late to get up)
travelling east phase advances our circadian rhythms (go to bed earlier and wake up earlier)
common disruptions of circadian rhythms - shift work
waking up/going to bed early is example of a phase advance
going to bed/waking up late is an example of phase delay
this can result in accidents (e.g. most lorry accidents occur between 4-7am, Chernobyl occurred between 1-4am)
common disruptions of circadian rhythms - age
age is a major determinant of sleep
amount of sleep decreases through childhood (newborn = 16-18 hours, adolescent = 8 hours)
in older age = sleep around 6-7 hours, more fragmented, more occasional night wake ups)
mechanisms of the biological clock - suprachiasmatic nucleus (SCN)
part of hypothalamus
main control centre of circadian rhythms of sleep and temperature
cells fire APs in particular rhythm
circadian rhythms generated by SCN are genetically controlled
SCN.- effect of light
light resets the SCN via a small branch of the optic nerve (retinohypothalamic path)
SCN - effect of light - where does the retinohypothalamic path come from
special population of retinal receptors that have their own photopigment called melanopsin
these cells directly respond to light, and do not require any input from the rods or cones
what role does the pineal gland have, and where is it located?
located posterior to the thalamus
secretes melatonin (hormone that increases sleepiness, and regulates circadian/circannual rhythms)
genetic basis of circadian rhythms - what are the two types of genes that are responsible for generating circadian rhythm
period - produce proteins called PER
timeless - produce proteins called TIM
when PER and TIM concentrations are high, they interact with a protein (clock gene) to induce sleepiness (opposite when they are low)
measures of sleep
EEG allowed researchers to discover that there are various stages of sleep
Polysomnography:
brain electroencephalograms (EEGs)
muscles electromyograms (EMGs)
heart electrocardiograms (ECGs)
eye movement electro-oculograms (EOGs)
what is an actigraph watch
recording device with an accelerometer (movement sensor)
what is the order of waves from slowest to fastest
donald trump ate baked goods
delta, theta, alpha, beta, gamma
what is stage 1 of sleep
sleep has just begun (light sleep)
EEG dominated by irregular, jagged, low voltage waves
5% of sleep time
what is stage 2 of sleep
beginning of true sleep
sleep spindles - 12-14Hz waves during burst that lasts at least half a second
K-complex - sharp high amplitude slow negative wave followed by a smaller, slower positive wave
50% of sleep time
what is stage 3 of sleep
slow wave sleep (SWS) “deep sleep”
EEG recording of slow, large amplitude wave (delta)
Slowing of heart rate, breathing rate, and brain activity
Highly synchronised neuronal activity
15-20% of sleep time
what is REM sleep
deep sleep in some ways, but light sleep in other ways
EEG waves are irregular, low-voltage and fast (as though awake/in Stage 1)
Postural muscles of the body are more relaxed than other stages
20-25% of sleep time
where in the brain are the wake and sleep centres
posterior hypothalamus the upper midbrain =
wake centre
anterior hypothalamus
preoptic area =
sleep centre
wake centre - brain stem
Receives sensory information
Brainstem plays an essential role in maintaining the state of wakefulness
Damage leads to coma
Stimulation of the reticular formation awakens animals from normal sleep or energises those already awake
mechanisms of sleep - neurotransmitters
inhibitory (GABA): decrease temp and metabolic rate, decrease stimulation of neurons
excitatory (Acetylcholine, Norepinephrine, Histamine, Orexin): increase arousal, maintain wakefulness, increases cortical activity
areas of the brain have increased/decreased activity during REM sleep - what are they?
Increased activity in the limbic system (emotional systems), parietal cortex and temporal cortex
Decreased activity in the primary visual cortex, the motor cortex, and the dorsolateral prefrontal cortex
functions of sleep - evolutionary theory
conserve energy (e.g., bats hunt at night time, body temp decreases during sleep to save energy)
functions of sleep - repair and restoration theory
sleep enables. body and brain to repair itself after working all day
evidence against repair and restoration theory
disturbances after sleep deprivation are mainly in attention tasks and not in complex cognitive tasks
No correlation between duration of sleep deprivation and the magnitude of performance deficits
Heavy physical (e.g., running a marathon) or mental exertion increase sleep only slightly
functions of sleep - improving cognitive function
Improving memory, decision making and many other executive functions
dreaming - what is the activation-synthesis hypothesis
Dream = effort to make sense of sparse and distorted information
Dreams begin with spontaneous activity in the pons, which activates many parts of the cortex (amygdala - important for emotion)
dreaming - what is the neurocognitive hypothesis
Dreams = thinking that takes place under unusual conditions.
Similar to the activation synthesis hypothesis in that dreams begin with arousing stimuli that are generated within the brain
