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NEURO > EEG, Sleep and Circadian rhythms > Flashcards

EEG, Sleep and Circadian rhythms Flashcards

1
Q

why does sleep occur

A

due to activite inhibitory processes in the pons

originates in the reticular formation nucleii of the brainstem

sends projections to the thalamus and higher cortical areas

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2
Q

what damage can create a brain that never sleeps

A

destruction of the brainstem at the level of the mid-pons

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3
Q

what drugs can inhibit sleep and why

A

reticular formation neurones are serotonergic

therefore drugs that block serotonin formation can inhibit sleep

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4
Q

how is the hypothalamus involved in sleep

A

electrical stimulation of tthe suprachiasmatic nuclei (SCN) of the hypothalamus stimulates release of melatonin - corresponds to feelings of sleepiness

also demonastrate 24hr circadian rhythm

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5
Q

what does damage to the SCN cause

A

disruption of the sleep-wake cycle

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6
Q

where is melatonin released from

A

the pineal gland

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7
Q

how is the hypothalamus involved in wakefulness

A

releases an excitatory neurotransmitter OREXIN (aka hypocretin)

orexin neurones active during waking state and stop firing during sleep

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8
Q

what can defective orexin signalling cause

A

narcolepsy

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9
Q

what happens during wakefulness (in terms of the reticular formation)

A

excitatory neurones in the ascending reticular activation system (ARAS) are released from inhibition from the sleep centres of the reticular formation

stimulate excitatory pathways in both the CNS and PNS

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10
Q

what happens when the excitatory cells for wakefulness become fatigued

A

excitatory signals fade

orexin levels fall

inhibitory peptide sleep signals from the sleep centres of the reticular formation take over and rapidly dominate

= rapid progression into sleep state

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11
Q

what happens when the inhibitory cells for sleep become fatigued

A

inhibitory signals fade

orexin levels rise

excitatory signals from the ARAS take over = wakefullness

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12
Q

what enables the awake state to be maintained

A

positive feedback from the CNS and PNS sustain it for many hours

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13
Q

what are the different ways you can assess the level of consciousness in an awake person

A 
behaviour
general alertness
speech patterns 
speech content 
reading
writing
calculating skills

record patterns of brain activity using an ElectroEncephaloGram (EEG) - electrodes places in scalp to record activity of underlying neurones

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14
Q

what do EEG recordings show

A

wave patterns that reflect the electrical activity of the brain

can be analysed by:
Amplitude: the size of the wave (ranges from 0-200 µV)

Frequency: number of waves per second (ranges from 1-50+)

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15
Q

what is the general trend between frequency seen and neural excitation

A

frequency increases with neuronal excitation

e.g. from lowest frequency to highest:
anaesthesia - sleep - awake relaxed - awake focused - tonic-clonic epilepsy

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16
Q

what are the 4 main types of wave pattern seen on EEG

A

Alpha
Beta
Theta
Delta

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17
Q

when are alpha waves seen

A

relaxed awake state

high frequency, high amplitude

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18
Q

when are beta waves seen

A

alert awake state

even higher frequency, low amplitude asynchronous

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19
Q

what explains the low amplitude of beta waves

A

high activity is asynchronous so opposing polarities of the signals cancel each other out and and so do not get recorded on EEG

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20
Q

when are theta waves seen

A

common in children and times of emotional stress and frustration in adults

occur during sleep

low frequency, very variable amplitude

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21
Q

when are delta waves seen

A

occur in deep sleep

low frequency, high amplitude

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22
Q

how many stages are there in the sleep cycle

A

5

23
Q

what occurs in stage 1 of the sleep cycle

A

Slow wave, non-REM, S-sleep.

Slow eye movements.

Light sleep.

Easily roused.

High amplitude, low frequency THETA waves

24
Q

what occurs in stage 2 of the sleep cycle

A

Eye movements stop.

Frequency slows further but EEG shows bursts of rapid waves called “sleep spindles”
(clusters of rhythmic waves, ~12-14Hz)

25
Q

what occurs in stage 3 of the sleep cycle

A

High amplitude,

very slow (2Hz) delta waves interspersed with short episodes of faster waves,

spindle activity declines

26
Q

what occurs in stage 4 of the sleep cycle

A

exclusively delta waves

27
Q

what occurs in stage 5 of the sleep cycle

A

REM sleep - rapid eye movements. Aka paradoxical sleep.

very fast waves - eerily similar to those of the awake state

Dreams occur during REM sleep. 25% of sleep is REM

28
Q

what stages are the deep sleep stages and what can occur during these stages

A

3 and 4

very difficult to rouse
sleep walking/talking

29
Q

what stages of sleep are slow wave sleep

A

1-4

30
Q

what are some physiological characteristics of deep, slow wave sleep

A
  1. occurs in the first few hours of sleep
  2. most restful type of sleep
  3. decreased vascular tone (drop in BP), respiratory and basal metabolic rate (drop in temp)
  4. dreams can occur but rarely remembered
31
Q

why is REM sleep known as paradoxical sleep

A

waves are are desynchronized, high frequency, low amplitude, very like the awake state

32
Q

what are some physiological characteristics of REM sleep

A
  1. lasts 5-30 mins every 90 mins - become more frequent as the night progresses
  2. dreams mostly occur here
  3. eye muscles show bursts of rapid activity
  4. HR/RR become irregular and brain metabolism increases
  5. EEG pattern mimics beta waves in awake status
  6. very difficult to rouse from REM but often we wake spontaneously from this stage in the morning
33
Q

what happens to skeletal muscles during REM sleep

A

profound inhibition due to inhibitory projections fro the pons to the spinal cord - prevent the acting out of dreams

34
Q

what can happen in REM sleep behavioural disorders

A

people can act out their dreams

35
Q

what happens when you are deprived of REM sleep

A

there is always a catch up on REM sleep when able to sleep again - indicates that REM sleep must have an important physiological function

36
Q

what would sleep deprived subjects demonstrate

A

Impairment of cognitive function

Impairment of physical performance

Sluggishness

Irritability

Psychosis has also been observed in some subjects

37
Q

what does sleep support

A

Neuronal plasticity

Learning and memory

Cognition

Clearance of waste products from CNS

Conservation of whole body energy

Immune function (reason sleep increases when ill?

38
Q

what happens to cerebral )2 consumption during sleep

A

increases, especially during REM sleep

39
Q

how do sleep patterns change throughout our lifetimes

A

total sleep time rapidly decreases through childhood and adolescence

percentage of REM sleep declines 
- 80% in 10 week premature baby
50% at full term 
- 25% in adulthood
- may be absent in 80+ yr olds
40
Q

list 5 common sleep disorders

A
  1. insomnia
  2. nightmares
  3. night terrors
  4. somnambulism (sleep walking)
  5. narcolepsy
41
Q

define insomnia

A

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

42
Q

what are the two type of insomnia

A

chronic primary - usually no identifiable psychological or physical cause

temporary secondary - in response to pain, bereavement or other crisis, usually short lived

43
Q

what do sleep lab studies on insomniacs show

A

EEG recordings for sleep onset and duration only marginally different to average
BUT
perception by the individual markedly different - can deny being asleep when awoken despite EEG readings indicating a change in arousal state

44
Q

what are some treatments for insomnia and their complications

A

barbiturates - chronic use increases time to fall asleep, decreases time in 3,4 and REM stages, increases no times awake during the night

benzodiazepines - less effects on REM but are addictive and can cause problems on withdrawal

45
Q

what happens during nightmares

A

strong visual component - seen during REM sleep, typically occurring quite far on through the night.

Waking will stop the nightmare and the individual will have a clear recollection of the dream

46
Q

what are night terrors

A

occur in deep, delta sleep

common in children 3-8 years, typically occurring early in the night - Children thrash and scream, may sit or stand up with their eyes open but are not properly awake and often fail to recognise their parents.

child does not remember the episode on waking the following morning

47
Q

what is somnambulism

A

sleep walking

occurs exclusively in non-REM sleep, mainly in Stage 4 sleep

is more common in children and young adults, probably due to the decline in Stage 4 sleep with age.

Somnambulists 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

have no recall of the episode when woken

48
Q

what is narcolepsy

A

Linked to dysfunctional orexin release from the hypothalamus

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.

49
Q

what is circadian rhythm

A

when biological systems show oscillations within a ~24hr period

50
Q

what controls circadian rhythm

A

suprachiasmatic nucleii on the hypothalamus just above the optic chiasma

contain an inherent 24hr cycle which is entrained by external cues such as light/dark cycles

51
Q

why light/dark cycles have an effect on circadian rhythm

A

some of the nerve fibres in the optic nerve pass into the SCN
BUT not only control as blind people still have a circadian rhythm

52
Q

what happens when the SCN is destroyed and why

A

loss of circadian rhythm

most likely due to loss of melatonin signalling and disruption of orexin signalling in the hypothalamus

53
Q

what can frequent changes in time zones or work patterns cause

A

disruption of behaviours particularly sleep and attention deficits

long term = 3x increase in CVS and GI disease

54
Q

what is the affect of blindness on dreams

A

born blind = auditory dreams

gradually go blind = eventually loose the inability to have visual dreams

NEURO (51 decks)

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