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Flashcards in Sleep & Consciousness Deck (24):

What are the inputs and outputs of the reticular formation?

Inputs (novel stimuli):
- visual impulses
- ascending general sensory tracts
- auditory impulses
- pain
- visceral somatosensory
- olfactory impulses

- radiations to cerebral cortex
- descending motor projections
- autonomic
- thalamus


How does smell affect the reticular activating system?

Olfactory impulses are the weakest input (therefore why one can sleep in a burning room despite the smoke)

Smelling salts elicit a nociceptive input to raise consciousness; not an olfactory input


What is the ascending reticular activating system?

Projections of reticular formation which raise the level of consciousness

Filters incoming signals e.g. repetitive/continuous unchanged stimuli ---> habituation

Filtering system reduced by LSD (increases sound sensitivity, hallucinations, "seeing colours")

Inhibited by:
- hypothalamic sleep centres
- alcohol
- hypnotic drugs
- anti-anxiolytics


Outline the thalamo-cortical loop.

Ascending reticular activation inhibits the thalamus and cerebral cortex

Thalamus inhibits the cerebral cortex

Cerebral cortex stimulates the thalamus and ascending activating system in order to prevent sleep despite need e.g. driving whilst tired

Thalamo-cortical loop generates oscillation on EEG


Outline the activity of the thalamo-cortical loop whilst awake or in paradoxical sleep.

Ach neurones from brainstem sensitise the thalamus to sensory signals ---> stimulate thalamo-cortical neurones

Thalamo-cortical neurones very active


Outline the activity of the thalamo-cortical loop in slow wave sleep.

Ach neurones in brainstem are less active

Thalamus inhibits the thalamo-cortical neurones

Thalamo-cortical neurones are less active


What is an EEG measuring? What might cause changes to an EEG?

Electroencephalography = algebraic sum of the electrical activity (excitatory and inhibitory) of neurones from the scalp

Causes of changes:
- brain damage
- dementia
- brain tumour
- epilepsy


Contrast the appearance of the brain waves in different parts of the brain.

- synchronised (awake with eyes shut) = high frequency, low amplitude waves
- desynchronised (awake with eyes open) = slightly reduced amplitude waves

- synchronised (awake with eyes shut) = high frequency, high amplitude waves
- desynchronised (awake with eyes open) = high frequency, low amplitude waves

- synchronised (awake with eyes shut) = alpha-waves/spindles; low frequency, large amplitude waves ("housekeeping" along with thalamocortical loops)
- desynchronised (awake with eyes open) = high frequency, low amplitude waves


What are the different types of non-REM brain waves?

- occipital lobes
- awake, quiet, eyes shut

- parietal and frontal lobes
- awake with eyes open

- parietal and temporal lobes
- children
- concentrating/meditating adults

- cortical
- deep sleep
- serious brain conditions
- thalamocortical oscillations


What is the EEG appearance in brain death?

No activity in brainstem or cortex


Contrast the areas of brain damage in locked-in syndrome and persistent vegetative state.

Locked-in syndrome = brainstem damaged by cortex intact
- can only move eyes up
- has consciousness, awareness, understanding

Persistent vegetative state = cortex damaged but brainstem intact
- awake (breathing and circulation intact +/- spontaneous movements, eye opening, facial expressions)
- no signs of awareness


Define coma. Give some examples of causes. What are some important investigations required?

State of unconsciousness from which the person cannot be roused using pain, sound, or light; and the patient does not initiate any voluntary movement

- intoxication or undercompliance (~40%)
- metabolic disorders e.g. DKA, hypothermia
- hypoxia (~20%)
- neurological
- trauma

- scans
- blood work
- history
- etc.


Why do we need sleep?

Old theory = energy conservation (but the brain is still active whilst asleep so not much energy is conserved)

CNS resetting/clearance e.g. glial washout of waste products

Memory (esp. during dreaming)

note: reduced sleep switches on "bad" genes


How is the sleep-wake cycle controlled?

Reticular formation

Hypothalamus = inhibits reticular formation ---> promotes sleep
(esp. active at 2AM-6AM and 2PM-4PM)

Biological clock (suprachiasmatic nucleus)
(interrupted in jet lag)

Caffeine = adenosine antagonist (adenosine builds in the hypothalamus to cause sleep)


Outline the different stages of sleep.

Takes ~1hr to get to deep sleep (delta waves) (10PM)

10PM-12AM = become more awake; transition from non-REM sleep (theta and alpha waves) to REM sleep (and then back to deep sleep)

12AM-7AM = periods of light non-REM sleep (theta waves) and REM sleep


Contrast the hormones active whilst awake and in non-REM and REM sleep.

- 5-HT and noradrenaline constantly active
- ACh neurones active during novel inputs

- 5-HT and noradrenaline inactive
- ACh inactive

- 5-HT and noradrenaline inactive
- ACh active (?memory without emotion)


What are the functions of non-REM sleep?

"Active body, inactive brain" (sleepwalking, bedwetting occur)


Majority of pituitary hormones released (effect of stress on hormones)

Overall reduction in BMR:
- reduced cerebral blood flow
- reduced O2 consumption
- reduced body temperature
- reduced BP
- reduced resp. rate


What are the functions of REM sleep?

"Active brain, inactive brain" (EEG appears as if awake - paradoxical sleep; prevents acting out dream via descending inhibition of motoneurones)

- inner ear (maintain pressure)
- eye muscles (rapid eye movements)
- resp. muscles

Dreaming; difficult to disturb

Irregular resp. rate and heart rate

Overall increase in BMR (~20%)
- increase in cerebral blood flow
- increase in O2 consumption
- increase in body temperature
- increase in BP
- increase in resp. rate

Reduced by alcohol (able to go to sleep quicker, but less refreshed)

Penile erection occurs (use to differentiate psychological v.s. physiological causes of erectile dysfunction)


Define insomnia. Give some examples of causes.

Inability to fall asleep or to remain asleep for an adequate length of time

e.g. stress ---> difficulty getting to sleep

e.g. depression ---> waking up in the middle of the night


Define parasomnia. Give some examples of different conditions encapsulated in this definition.

Sleep disorders involving abnormal movements, behaviours, emotions, perceptions, and dreams

e.g. bedwetting

e.g. sleepwalking (+ other activities whilst asleep)

e.g. "night terrors"

e.g. sleep paralysis (wake up - cortex active - but cannot move - motor neurones still inhibited)


Define hypersomnia. Give some examples of conditions encapsulated within this definition.

Excessive daytime sleepiness or prolonged night-time sleep

e.g. narcolepsy = loss of brain's ability to regulate sleep-wake cycles due to a lack of protein in the hypothalamus

e.g. obstructive sleep apnoea = loss of tone of upper resp. tract muscles (increased fat, septum problems) causing closure of the airways which causes snoring and wakefulness (think they have slept all night but are constantly disturbed so they have little deep sleep)


Outline the management of obstructive sleep apnoea.

Sleep study


Prevent from rolling onto back e.g. tennis balls

Singing (increased tone of upper resp. tract muscles)


What are the functions of the reticular formation?

Sleep regulation (ascending reticular formation system raises the level of consciousness)

Motor control

Cardio/resp. control


Motivation and reward e.g. "Do I need to concentrate?", "Do I need to be quiet?"


How is consciousness assessed?

Glasgow Coma Score (/15)

Lowest possible score is 3/15 (completely unconscious)

Eye Opening:
4 = spontaneously
3 = speech
2 = pain
1 = none

Motor Response:
6 = obeys commands
5 = localises pain (moves away from/pushes away painful stimuli)
4 = flexion to pain (specific e.g. move finger away)
3 = flexion/withdrawal (whole limb or abnormal)
2 = extension to pain
1 = none

Verbal Response:
5 = orientated
4 = confused
3 = inappropriate words
2 = incomprehensible
1 = none

note: can be affected by normal neurological function but poor voluntary compliance (motor response is the most reliable)

note: patterns of change in GCS are more important than the precise number (as it indicates a change in brain function)