Sleep Flashcards
what is sleep?
state of unconsciousness from which an individual can be aroused by normal stimuli= light, touch, sound etc and is predictable and cyclical
what happens when we are sleep deprived?
impairment of cognitive function and physical performance, sluggishness and irritability
what are the 6 things that sleep supports?
neuronal plasticity, learning and memory, cognition, clearance of waste products from the CNS, conservation of whole-body energy and immune function
why does sleep occur?
active inhibitory processes in the recticular formation of the brainstem where arousal centres and sleep centres exist - our level of conciousness depends on the balance of activity between the 2 - the day is dominated by activity from the arousal centres but their activity switches throughout the day and the sleep centre will dominate at night so we fall asleep and the cycle repeats
what molecules are believed to contribute to sleep?
delta sleep inducing peptides (DSIP), adenosine, melatonin and serotonin
how does DSIP contribute to sleep?
when removed from animals from CSF who have been sleep deprived and injected into the brains of different animals, they will produce an almost instantaneous sleep
how does adenosine contribute to sleep?
levels build up through the day and when they reach a threshold we get the formation known as sleep pressure which is the feeling of sleepiness - adenosine receptors are antagonised by caffeine and so caffeine late at night will keep you awake as you will lose this sleep pressure
how does melatonin contribute to sleep?
shows very strong circadian rhythm and is highest during the night when we are sleeping
how does serotonin contribute to sleep?
it is a precursor to melatonin
where is melatonin produced and what influences this?
produced in the pineal gland and is under the influence of the suprachiasmatic nucleus (SCN) in the hypothalamus
what is the circadian rhythm and its main regulator?
the circadian rhythm regulates sleep and is mainly regulated by the SCN whose activity matches the release of melatonin from the pineal gland
what controls the acitivity of the neurones in the SCN?
inhibitory neurones in the SCN are stimulated by light and act to inhibit the pineal gland and darkness will remove this inhibition causing stimulation of the pineal gland
how do melatonin levels affect nocturnal animals?
the rise in melatonin will wake them up but the cycle and stimuli are the same so that they can stay awake at night
what is orexin (also called hypocretin)?
excitatory neurotransmitter released from the hypothalamus and is required for wakefulness (as excitatory)
what is the pattern of orexin neurones?
there are active during the waking state and stop firing during sleep
what does defective orexin signalling cause?
narcolepsy= the individual will suddenly fall asleep
why is serotonin critical to sleep induction?
many neurones within the recticular formation are serotonergic and so drugs that block serotonin formation inhibit sleep
what happens to serotonin during depression?
decrease in serotonin in the synapse and individuals who are depressed often struggle to sleep due to this
how can depression therefore be treated?
serotonin selective reuptake inhibitors (SSRIs) which increase serotonin levels in the synapse which helps treat depression and restore normal sleep cycles
what is an electroencephalogram (EEG) and what does it measure?
electrodes are placed on the scalp and record activity of the underlying neurones and the patterns reflect the electrical activity of the brain (which it measures)
how can the waves of the EEG be analysed?
amplitude= size of the wave and frequency= number of waves per second
what are the general rules for frequency and amplitude in relation to consciousness?
frequency increases with neuronal excitation so longer wavelengths= more unconsciousness and smaller wavelengths= more alert
amplitude is the opposite and decreases with increasing neuronal excitation
what do the waves of deep surgical anaesthesia look like?
very long waves with low frequency
what do the waves of epilepsy look like?
abnormally frequent- very short waves
what are the 4 main types of wave pattern seen?
alpha, beta, theta and delta
what are alpha waves associated with?
relaxed awake state- high frequency, medium amplitude waves
what are beta waves associated with?
alert awake state- very high frequency, low amplitude waves
what are theta waves associated with?
early sleep- low frequency waves which can vary enormously in amplitude
what are delta waves associated with?
deep sleep- very low frequency but high amplitude waves
why do beta waves have a low amplitude if they are in the alert and awake state?
not because of low activity but because of high activity which is asynchronous as brain is doing so many things at once and so opposing polarities of the signals cancel each other out and so are not recorded on EEG
what will an EEG look like when someones eyes are open compared to closed but awake?
awake but eyes closed= longer wavelength and less waves but amplitude greater than when eyes open= frequency increases and amplitude decreases and opposing polarities cancel out the waves
what happens the the relaxed state?
less external stimuli being processed so the waves are synchronised causing increased amplitude as the waves are superimposed on top of each other but low frequency
what happens in the high-alert state?
lots of information coming into the brain randomly so the brain is stimulated in a random way and the waves are asynchronous and end up cancelling each other out
what at the first stage of sleep?
slow wave, non-REM, S-sleep - very light sleep so can be easily aroused, high amplitude, low frequency theta waves, not yet reached stage of unconsciousness
what is the second stage of sleep?
eye movements stop, frequency slows further but EEG shows burst of rapid waves called sleep singles
what is the third stage of sleep?
high amplitude, very slow delta waves interspersed with short episodes of faster waves, spindle activity declines
what is the fourth stage of sleep?
exclusively delta waves
what stages are deep sleep?
stage 3 and 4 which are very difficult to rouse from
what is the cyclical pathway of sleep?
1 - 2 - 3 - 4 - 3 - 2 - REM - 2 - 3 - 4 - 3 - 2 - REM etc
what is REM sleep?
rapid eye movements occur (25% of sleep)- low amplitude and high frequency (small as awake state) - as time asleep increase so does our time spent in REM sleep
what are the physiological characteristics of deep, slow wave sleep?
most restful, decreased vascular tone and so BP, respiratory and basal metabolic rate and so BT, hippocampus is very active due to creation of new memories while we are sleeping
what are the physiological characteristics of REM sleep?
lasts 5-30 mins every 90 minutes, dreams mostly occur due to new neuronal connection being made, eye muscles also show bursts of rapid activity
what is REM sleep behavioural disorder?
normally skeletal muscles are inhibited from moving during sleep which prevents acting out dreams but this inhibition is lacking in some people so they can act out their dreams
how does sleep change over a lifetime?
total sleep decreases rapidly through childhood and adolescence and % of REM sleep also declines - also declines in old age which may be partially responsible for associated cognitive decline
what is insomnia?
chronic inability to obtain the necessary amount or quality of sleep to maintain adequate daytime behaviour - very subjective and can be chronic or temporary (usually associated with pain, bereavement or another crisis)
how is insomnia treated?
preferably adoption of behaviours that promote sleep= good sleep hygeine as sleeping tablets make you sleepy during the day
what are nightmares?
bad dreams seen in REM sleep
what are night terrors?
occur in deep, delta sleep and are common in children - they will thrash and scream and their eyes will be open but they will not remember the episode in the morning
what is somnambulism (sleepwalking)?
only in non-REM sleep, mainly stage 4 and more common in children- they appear awake and will avoid objects and obey instructions but will not recall
what is narcolepsy?
enter into REM sleep with little warning, accident risk and linked with dysfunctional orexin release from the hypothalamus
what are the long-term effects of frequent changes in time zones and work patterns like short workers and flight crews?
increased risk of CVS and GU diseases after 10 years 3x increase
