Sleep Flashcards
Why does sleep occur
due to active inhibitory processes that originate in the pons
Something below the level of the mid-pons is doing what?
actively sending inhibitory impulses to the cortex - this inhibits skeletal muscles in order to stop us from acting out our dreams (sometimes this can fail)
where does evidence suggest sleep activity originates from?
reticular formation of the brain stem - it is closely associated with controlling the state of consciousness
Many neurons within the reticular formation are of which type?
serotonergic
How do drugs enable sleep induction
they block serotonin formation
Define ‘sleep’
a state of unconsciousness that we can be aroused from by things like light, touch, sound
Describe why you start to feel tired as the day goes on
Arousal centers send stimulatory signals.
Higher outflow makes you feel more awake – goes on throughout the day. When they reach their peak towards end of the day, firing dampens down
Stronger signals – inhibitory – when you start to feel tired again
Arousal centres switched off at night.
What 2 other things are involved in sleep other than reticular formation?
hypothalamus and it’s suprachiasmatic nuclei (SCN)
If you stimulate SCN what outcome does this have?
promotes sleep
Function of SCN
controls release of melatonin
where is melatonin released from
pineal gland
What are inhibitory neurons in SCN stimulated by?
light - they act to inhibit the pineal gland to delay the release of melatonin until later when darkness arrives
what happens when light hits your eye?
When you see light – neurons travel to SCN - inhibitory signals from the SCN then travel to pineal gland - switch off melatonin release
What is orexin?
it is an excitatory transmitter - associated with inducing wakefulness
Defective orexin firing causes what?
Narcolepsy - suddenly fall asleep
How do you assess someone’s level of consciousness when they’re awake (2)
Look at their behaviour, general alertness, speech patterns, speech content, reading, writing and calculating skills. Spell words backwards or count backwards.
Record patterns of brain activity using ElectroEncepheloGram (EEG). EEG uses electrodes placed on the scalp to record activity of underlying neurons.
What drugs are commonly used to treat depression where sleep disruption is present?
Serotonin selective reuptake inhibitors - acts to increase serotonin levels in synapse
How can EEG waves be analysed? (2)
Amplitude - size of wave
Frequency - no of waves a second
What is the general trend with frequency and neuronal excitement?
In general, frequency increases with neuronal excitation where as the wavelength decreases
What are the 4 main types of wave pattern?
Alpha
Beta
Theta
Delta
What is the wave pattern like in the relaxed, awake state?
high frequency, high amplitude waves termed alpha waves
What is the wave pattern like in the alert, awake state?
EEG is characterised by even higher frequency, low amplitude asynchronous waves termed beta waves
How does low amplitude come about
Brain doing lots of things, lots of desynchronised waves cancel each other out, so amplitude is low but frequency high
How are Theta waves characterised?
Low frequency waves which can vary enormously in amplitude.
Common in children, and during times of emotional stress and frustration in adults. Occur during sleep in both adults and children
How are Delta waves characterised?
Delta waves have very low frequency but high amplitude. They occur in deep sleep. Low stimuli.
Summary of four main waves and when they occur
Alpha - relaxed, awake
Beta - Alert, awake
Theta - times of emotional stress/frustration and during sleep in adults and children
Delta - deep sleep
What are the 5 stages of sleep
Stage 1, 2, 3, 4 and REM sleep
What happens in stage 1 of sleep
Slow wave, non-REM, S-sleep.
Slow eye movements. Light sleep.
Easily roused.
High amplitude, low frequency theta waves.
What happens in stage 2 sleep?
Eye movements stop. Frequency slows further but EEG shows bursts of rapid waves called “sleep spindles” (clusters of rhythmic waves, ~12-14Hz)
What happens during stage 3 of sleep
High amplitude, very slow (2Hz) delta waves interspersed with short episodes of faster waves, spindle activity declines.
What happens during stage 4 of sleep
Exclusively delta waves (deep sleep)
What happens during REM sleep
Rapid eye movements. Dreams occur during REM sleep. 25% of sleep is REM.
What is the cyclical order during sleep?
Stage 1 (when your head hits pillow) - 2 - 3 - 4 - 3 - 2 - REM - 2 - 3 - 4 and so on
Following initial S-wave sleep of stages 3 and 4, there is a gradual awakening towards Stage 1, but not like the initial Stage 1, instead REM sleep during which EEG waves are desynchronized, high frequency, low amplitude, very like the awake state hence aka. paradoxical sleep.
Why is REM sleep often referred to as ‘paradoxical sleep’
REM sleep is characterised by fast waves, eerily similar to those of the awake state.
On and EEG, it would look like they were awake
True or false: The frequency of REM sleep increases throughout the night/sleep cycle
True
What happens during deep sleep that occurs in the first hours of sleep?
Most restful type of sleep.
Associated with decreased vascular tone (and therefore BP), respiratory and basal metabolic rate (hence drop in BT).
Dreams may occur but are rarely remembered.
What drug increases the time spent in REM sleep?
Anticholinesterases
How would a sleep-deprived patient present? (4)
Impairment of cognitive function
Impairment of physical performance
Sluggishness
Irritability
What does sleep help support in the body? (6)
Neuronal plasticity
Learning and memory
Cognition
Clearance of waste products from CNS
Conservation of whole body energy (although cerebral O2 consumption may actually increase, esp. during REM sleep)
Immune function (reason sleep increases when ill?)
Insomnia
defined as a “chronic inability to obtain the necessary amount or quality of sleep to maintain adequate daytime behaviour”,
very subjective (everyone needs different amount of sleep), very common.
Affects 33% of adults.
Temporary - tends to be short lived - pain, bereavement or other crisis
Chronic - usually no cause known
treatment - behavioural changes, promote healthy sleep habits
hypnotic sleeping drugs have bad side effects
Nightmares
strong visual component and are seen during REM sleep,
Waking will stop the nightmare and the individual will have a clear recollection of the “dream”.
Night terrors
occur in deep, delta sleep and are common in children 3-8 years, typically occurring early in the night.
Children thrash and scream and may sit or stand up with their eyes open but are not properly awake and often fail to recognise their parents.
The child does not remember the episode on waking the following morning.
Somnambulism (sleep walking)
occurs exclusively in non-REM sleep, mainly in Stage 4 sleep and is more common in children and young adults
Usually walk with their eyes open, can see and will avoid objects, can carry out reasonably complex task such as prepare food and will often obey instructions but have no recall of the episode when woken.
Narcolepsy
enter directly into REM sleep with little warning - fall asleep at any time - linked to dysfunctional orexin release
Very dangerous because of accident risk if e.g. driving.
