EEG, Sleep and Circadian Rhythms Flashcards
why does sleep occur?
active inhibitory processes that originate in the pons
what does electrical stimulation of the SCN promote?
sleep
what does damage to the SCN disrupt?
sleep-wake cycle
what does activity of the SCN stimulate release of?
of melatonin from the pineal gland
what else does the hypothalamus release?
releases an excitatory neurotransmitter orexin (aka hypocretin) which is required for wakefulness
when are orexin neurones active?
during the waking state and stop firing during sleep
what does defective orexin signalling cause?
narcolepsy
how does one asses the level of consciousness in an awake person?
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.
how are the waves measured?
Amplitude
Frequency
what is the amplitude?
size of the wave
what is the frequency?
number of waves per second
frequency …. with neural excitation
increases
what are the four main types of wave pattern?
alpha
beta
theta
delta
how is the EEG characterised in a relaxed awake state?
high frequency, high amplitude waves termed a waves.
how is the EEG characterised in an alert awake state?
by even higher frequency, low amplitude asynchronous waves termed B waves. Low amplitude comes about, not because of low activity, but precisely the opposite.
hhow are theta characterised by?
low frequency waves which can vary enormously in amplitude. They are common in children, and during times of emotional stress and frustration in adults. They also occur during sleep in both adults and children.
how are delta waves characterised?
have very low frequency but high amplitude. They occur in deep sleep
how many stages of the sleep cycle is there?
5
what is stage 1 of the sleep cycle?
Slow wave, non-REM, S-sleep. Slow eye movements. Light sleep. Easily roused. High amplitude, low frequency theta waves.
what is stage 2 of the sleep cycle
Eye movements stop. Frequency slows further but EEG shows bursts of rapid waves called “sleep spindles” (clusters of rhythmic waves, ~12-14Hz)
what is stage 3 of the sleep cycle?
High amplitude, very slow (2Hz) delta waves interspersed with short episodes of faster waves, spindle activity declines
what is stage 4 of the sleep cycle?
exclusively delta waves.
what stages do sleep walking/talking happen?
3 and 4
what is stage 5
REM
at what stage is slow wave sleep?
1-4
what are physiological characterstics of deep, slow wave sleep?
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.
when does REM happen?
Lasts 5-30mins every 90mins or so during a normal nights sleep, becoming more frequent as night progresses and rest and recovery are established.
state the characteristics of REM
dreams occur
rapid burst of activity on eye muscles
dependent on cholinergic pathwayspathways within the reticular formation and their projections to the thalamus, hypothalamus and cortex. Anticholinesterases increase time spent in REM sleep.
REM causes HR/RR to become irregular and brain metablolism increases. EEG mimics beta waves
difficult to arouse an individual from REM sleep.
Whenever deprived of REM sleep, there is always a catch up when able to sleep again indicating that REM sleep must have an important physiological function
what do sleep deprived subjects demonstrate?
Impairment of cognitive function
Impairment of physical performance
Sluggishness
Irritability
in the importance of sleep, what does sleep support?
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?)
when is total sleep time greatest?
during development when brain maturation and synaptic formation is occurring rapidly
how much of the population is effected by sleep disorders?
25%
what is insomnia defined as?
“chronic inability to obtain the necessary amount or quality of sleep to maintain adequate daytime behaviour”, very subjective, very common. Affects 33% of adults.
whats the difference between chronic and temporary insomnia?
chronic, primary insomnia where there is usually no identifiable psychological or physical cause
temporary, secondary insomnia in response to pain, bereavement or other crisis. Usually short lived.
drugs to treat insomnia, especially barbiturates, have been shown to depress what type of sleep?
REM and delta sleep
wht does chronic use of drugs for insomnia do to sleep?
increases time taken to fall asleep, decreases time spent in REM and stage 3 and 4 sleep, and increases no. of times awake during night.
when does nightmares occur?
during REM sleep
when do night terrors occur?
deep, delta sleep and are common in children 3-8 years, typically occurring early in the night
what is somnambulism?
slep walking
when does somnambulism likely occur?
exclusively in non-REM sleep, mainly in Stage 4 sleep and is more common in children and young adults, probably due to the decline in Stage 4 sleep with age.
what is narcolepsy?
Patients enter directly into REM sleep with little warning. Symptoms could be interpreted as intrusion of REM sleep characteristics onto the waking state. Very dangerous because of accident risk if e.g. driving.
Linked to dysfunctional orexin release from the hypothalamus
what is circadian rhythm?
biological systems show oscillations with an 24 hour period.
where is the “master clock” located?
suprachiasmatic nucleus (SCN) of the hypothalamus, lying just above the optic chiasma
what is significant about the suprachiasmatic nucleus?
These neurons have an inherent 24 hour cycle which is entrained by external cues such as light/dark cycles, probably because some of the nerve fibres in the optic nerve pass to the SCN. However this cannot be the only entrainment as blind people also have circadian rhythms.
what happens to the circadian rhythm if the SCN is destroyed and why?
the circadian rhythm is lost. this is most likely due to the loss of melatonin signalling and disruption of orexin signalling in the hypothalamus.
what does destruction of the brainstem at the level of the mid-pons create?
a brain that never sleeps
what are inhibitory neurones in SCN stimulated by?
light and act to inhibit pineal gland. Darkness therefore corresponds with decreased activity in the SCN and increased melatonin release and feelings of sleepiness in humans.
what is orexin?
an excitatory neurotransmitter released from hypothalamus- required for wakefulness
what are the neurons within the reticular formation called?
serotonergic
what are serotonergic neurons?
drugs that block serotonin formation inhibit sleep suggesting serotonin must be critical to sleep induction.
what is serotonin a precurser for?
melatonin
