EEG, Sleep and Circadian Rhythms Flashcards by Emilia Sykes

Explain the theory of sleep?

1) Sleep occurs due to active inhibitory processes that originate in the pons
2) Destruction of brainstem at level of mid-pons creates a brain that never sleeps, so something below this must be actively sending inhibitory impulses to the cortex
3) Activity originates in the reticular foramen (evidence suggests) of the brainstem, which is closely associated with controlling state of consciousness
4) Sends projections to the thalamus and higher cortical areas

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What part of the hypothalamus does evidence suggest is involved in sleep?

Hypothalamus and its suprachiasmatic nuclei (SNC) are involved in inductino of sleep

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What does SCN stand for?

Suprachiasmatic nuclei

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What does the SNC inhibit the release of with its 24 hour circadian rhythm?

Melatonin

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What are the inhibitory neurons in the SCN stimulated by?

Light and act to inhibit the pineal gland, darkness therefore corresponds with decreased activity in the SCN and increased melatonin release and feelings of sleepiness

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What is melatonin produced by?

Pineal gland

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What is the circadian rhythm?

24 hour cycle in physiological processes of living beings

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What is the circadian rhythm of melatonin release likely linked to the inhibition of?

Orexin

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What is orexin?

Excitatory neurotransmitter released from hypothalamus required for wakefulness

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Are orexin neurons active during the waking state or when asleep?

During the waking state and stop firing during sleep

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How does decreased activity of SCN impact melatonin release and orexin?

Decreased orexin

Increased melatonin

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What does defective orexin signalling cause?

Narcolepsy where the individual will suddenly fall asleep sometimes even when they are talking

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What is the relationship between serotonin and sleep?

Many neurons within reticular foramen are serotonergic

Drugs that block serotonin formation inhibit sleep suggesting serotonin must be crucial to sleep induction

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What does assessing the level of consciousness in an awake person involve?

Look at behaviour, general alertness, speech patterns, speech contents, reading, writing and calculating skills

Spell words backwards or count backwards

Record patterns of brain activity with electroencephlogram (EEG)

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What does EEG stand for?

Electroencephalogram

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What is an electroencephalogram (EEG)?

Uses electrodes placed on scalp to record brain activity of underlying neurons, showing wave patterns that reflect the electrical activity of the brain

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What can the waves produced by an EEG be analysed by?

Amplitude (the size of the wave)

Frequency (the number of waves per second)

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What is the range of amplitude of brain waves on an EEG?

From 0-200uV

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What is the range of frequencies of brain waves on an EEG?

1 to 50+

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How does frequency and amplitude of brain waves change with neuronal excitation?

Frequency - increased with neuronal excitation

Amplitude - decreases with neuronal excitation

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What are the four main types of wave patterns seen on an EEG?

Alpha

Beta

Theta

Delta

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What are EEG waves characterised by in relaxed, awake state?

High frequency

High amplitude

this is termed alpha waves

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What are EEG waves characterised by when in alart, awake state?

Even higher frequency waves than alpha

Low amplitude asynchonous waves (due to brain doing many things at once so opposing polarities cancel each other out and do not get recorded on EEG)

this is termed beta waves

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What is the amplitude and frequency like of alpha waves?

High amplitude

High frequency

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What is the amplitude and frequency like of beta waves?

Low amplitude Even higher frequency than alpha waves

What is the amplitude and frequency like in theta waves?

Low frequency Enourmous variation in amplitude

Who are theta waves common in?

Children during times of emotional stress and frustration in adults Also occur duing sleep in both adults and children

What is the amplitude and frequency like of delta waves?

Very low frequency High amplitude

When do delta waves occur?

During deep sleep

How many stages are there in the sleep cycle?

Explain the 5 stages of sleep?

1. Slow wave, non-REM, S-sleep. Slow eye movements. Light sleep. Easily roused. High amplitude, low frequency theta waves 2. Eye movements stop. Frequency slows further but EEG shows bursts of rapid waves called “sleep spindles” (clusters of rhythmic waves at 12-14Hz) 3. High amplitude, very slow (2Hz) delta waves interspersed with short episodes of faster waves, spindle activity declines 4. Exclusively delta waves 5. REM sleep, during which there are rapid eye movements. Dreams occur here. About 25% of sleep is this.

What are sleep spindles?

Clusters of rhythmic waves at 12-14Hz

What stage of the sleep cycle is exclusively delta waves?

Stage 4, just before REM sleep

What stages of the sleep cycle are known as deep sleep?

Stages 3 and 4

During what phases of the sleep cycle does sleep walking/talking occur?

Stages 3 and 4 (deep sleep)

What is the amplitude like in the stages of deep sleep?

Large amplitude

How does the frequency of waves compare between REM sleep and stages 1 to 4?

Frequency is much greater in REM sleep, eerily similar to the awake stage

What are some characteristics 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 base metabolic rate Dreams may occur here but are rarely remembered

What is REM sleep also known as?

Paradoxical sleep

Are waves synchonised in S-wave or REM sleep?

S-wave sleep

How long does REM sleep last per 90 minutes?

5-30 minutes

Does REM sleep become more or less frequent as the night progresses?

More frequent so rest and recovery is established

In what stage of sleep do dreams mostly occur in?

REM sleep

In what stage of sleep do the eyes move the fastest?

REM sleep, shows bursts of rapid activity

What are the skeletal muscles like in REM sleep?

Inhibited due to inhibitory projections from pons to spinal cord, preventing acting out of dreams

What pathways is REM sleep dependent on?

Cholinergic pathways within reticular formation and their projections to the thalamus, hypothalamus and cortex

How do anticholinesterases change the amount of time spent in REM sleep?

Increases the amount of time

How does the HR, RR, brain metabolism change in REM sleep?

HR/RR becomes irregular Brain metabolism increased

What waves does the EEG show during REM sleep?

Beta waves associated with highly alert awake state

What things do sleep deprived subjects demonstrate?

Impairment of cognitive function Impairment of physical performance Sluggishness Irritability Psychosis is observed in some subjects

What things 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, especially during REM sleep) Immune function

How does sleep time change through childhood and adolescence?

Decreases rapidly

How does the percentage of REM sleep change through childhood and adolescence?

Declines: 80% in 10 week premature infant 50% at full term declining to a stable 25% in adulthood may be absent by 80+

In adulthood, what percentage of sleep is REM sleep?

25%

What percentage of the population are affected by sleep disorders?

Up to 25%

What are examples of sleep disorders?

Insomnia Nightmares Night terrors Somnambulism (sleep walking) Narcolepsy

What is the medical term for sleep walking?

Somnambulism

What is insomnia?

Chronic inability to obtain the necessary amount or quality of sleep to maintain adequate daytime behaviour

What is the prevalence of insomnia?

33% of adults

What are the different kinds of insomnia?

Chronic, primary insomnia (no identifiable psychological or physical cause) Temporary, secondary insomnia in response to pain, bereavement or other crises

What drugs are used to treat insomnia?

Barbiturates (but depress REM sleep and delta sleep) Benzodiazepines (less effect on REM sleep but addictive)

What is the preferred approach to treat insomnia?

Change in behaviour to support induction of sleep, not drugs as have many side effects

In what stage of sleep are nightmares usually experienced?

During REM sleep

In what stage of sleep do night terrors occur in?

Deep, delta sleep

How does the timing of nightmares and night terrors compare?

Night terrors occur early in the night Nightmares occur late in the night

Who are night terrors common in?

Children aged 3 to 8, where they trash and scream and may sit or stand up with their eyes open but are not properly awake and fail to recognise their parents

During what stage of sleep does somnambulism normally occur?

Non-REM sleep, mainly in stage 4

How is somnambulism most common in?

Children and young adults, probably due to decline in stage 4 sleep with age

What is the prevalence of narcolepsy?

1:2000

What kind of sleep do people with narcolepsy enter directly into?

REM sleep

What is narcolepsy linked to the dysfunction of?

Dysfunctional orexin release from the hypothalamus

What is orexin released from?

Hypothalamus