Physiology of Sleep Flashcards
What is - a natural periodic state of rest for the mind and body - in which eyes usually close and consciousness is completely or partially lost, so there is a decrease in bodily movement and responsiveness to external stimuli?
Sleep
How much of our lives is spent sleeping?
Approx 1/3
Are sleeping patterns uniform for everyone?
No - some people need more sleep, some less.
How does old age impact on sleep?
Sleep can become fragmented in old age - thought to attribute to various ailments as we get older.
How can a lack of sleep impact on a person?
Can lead to significant impact on physiological as well as psychological well being - inc. affecting memory, temper, language and sense of time.
How can we measure sleep?
Questionnaires
Physiological measurements - e.g. EEG, using biomarkers
What is wrong with the questionnaire approach to assessing sleep?
Subject to interpretation by P, increased levels of error due to bias
Why are physiological methods better for measuring sleep quality?
They are free from base and have reproducible results.
Which method involves recording a gross average of electrical potentials of cells and fibres in the brain area close to an electrode?
EEG
Which method involves recording a gross average of electrical potentials of cells and fibres in the brain area close to an electrode?
EEG
What does EEG stand for?
Electroencephalography
How does an EEG work?
Neurones generate electric potentials in the brain - some positive, some negative. The electrode on the scalp works out the sum total of charge in that area and reports it on a graph = brain waves
How many neurons are usually detected by one electrode?
About 10,000
What happens to the brain when there is no stimulus?
The neurons form a rhythmic pattern = synchronous rhythm on the EEG
What are the basic requirements for signal detect?
Neurons must be active in synchrony to generate large enough electrical field to be detected from the scalp
Neurons must be aligned in parallel orientation - so they summate rather than cancel out
What does amplitude of the EEG signal depend on?
Number of active cells, total amount of excitation & timing of activity
How does an awake brain appear on EEG
Irregular rhythm, high frequency but low amplitude waves
How does an asleep brain appear on EEG?
Regular rhythm, with low frequency and high amplitude waves
Why do brain waves appear even when neurons are not being stimulated?
Thalamic cells = voltage-gated ion channels - self-discharge at rhythmic intervals even in the absence of external input.
Thalamic pacemaker neurons become synchronised via cellular and chemical communication. = Regular pattern on EEG
Which ions passthrough thalamic pacemaker neurons?
Na, K & Ca
What are the functions of brain rhythms when asleep?
We dont know
How does increased, synchronised activity appear on EEG?
As larger amplitude waves
What physiological responses occur when we are asleep?
Decreased in HR, RR & brain activity
What behavioural changes occur when we are asleep?
Lack of gross movement
Rapid Eye movement cycles
How many sleep cycles do we experience during the night?
6-7
What are the stages of sleep?
Awake
Stage 1 - NREM
Stage 2 - NREM
Stages 3-4 NREM
REM
What are the stages of sleep?
Awake
Stage 1 - NREM
Stage 2 - NREM
Stages 3-4 NREM
REM
Name the stages of sleep on this EEG
How many stages of non-rem sleep are there?
4
What identifies Stage 1 NREM (N1)?
Irregular, jagged, low-voltage waves.
Brain activity is high - but starts to decline
What identifies Stage 2 NREM (N2?)
Sleep Spindle and K-complex presence
What is the sleep spindle?
A frequency of 12-14 Hz burst for at least 500ms.
What is the sleep spindle?
What is it generated by?
A frequency of 12-14 Hz burst for at least 500ms
Generated by oscillating interactions between the thalamus and the cortex
How can you identify the K-complex? What is it caused by?
Is a sharp high-amplitude positive wave followed by a smaller slow negative wave.
Occurs randomly and in response to auditory stimuli. Brain is responsive to the stimuli and monitors but doesn’t necessarily wake up from it
How can you identify stages 3 & 4 of NREM sleep?
Have δ waves = slow, large amplitude, regular waves
What are stages 3&4 of NREM sleep known as?
Slow-wave sleep (SWS)
At which stage of sleep can sleepwalking, nightmares and bed wetting occur?
Stages 3&4 NREM
How does REM sleep appear on EEG?
Irregular, low voltage fast waves (similar to Stage 1).
What happens during REM sleep?
Increased brain activity - may be because of dreaming
Which sleep cycle is most important to awake rested?
REM
How many stages of REM sleep do you get a night?
5-6
Which stage is the brain most active and the body the least active in?
REM sleep
What happens when you transition from NREM to REM sleep?
You awake slightly before entering REM sleep
What physiological changes occur during REM sleep?
Postural muscles become more relaxed
HR, RR & BP are more variable than other stages
Increased blood supply to reproductive organs
How long does the entire sleep cycle last?
90-120 mins
Humans cycle from Stage 1 to REM during the first cycle of sleep. What happens in subsequent cycles?
Subsequent cycles start from stage 2 to REM every 90-110 mins
Which drugs are best for inducing sleep?
Benzodiazepines
How do benzodiazepines work?
Are GABA A modulators - modulate the Cl channel - allowing it to stay open longer - thus hyper polarising the cell = induction of sleep.
How do benzodiazepines affect the sleep cycle?
Increase N1 & N2 but decrease N3&4 and REM sleep
What is a big problem with benzodiazepines?
Dependance
What are the limitations of the EEG?
No sensitive enough to pick up individual APs
Cannot distinguish between excitation, modulatory or inhibitory activity
Limited anatomical specificity
Which scan is best for anatomical specificity of brain waves?
What is its drawback?
fMRI best
Very expensive
Which hormones are involved in circadian rhythm?
Cortisol (day) and Melatonin (night)
How does the circadian clock work?
Is present in the brain - receives information from light and regulates production of melatonin and cortisol, controlling sleep cycle. Also sets the peripheral clocks.
What things are controlled by the peripheral circadian clocks?
Excretion, digestion, urination - synchronise internal organs
Name 2 types of NREM parasomnias
Sleepwalking
Night Terrors
Name one type of REM parasomnias
Sleep Behavioural Disorder
What is a sleep-related disorder called?
Parasomnia
What disorder is this?
P gets out of bed whilst still asleep, exhibits limited awareness and responsiveness to surroundings
Sleep walking (NREM)
What disorder is this?
P often screams in sleep - most are not responsive to outside stimuli and have no recollection of the source for their terror upon waking.
Night Terrors (NREM)
What disorder is this?
Unusual vocalisations or movements during REM sleep,
