Sleep & Consciousness Flashcards
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
Outputs:
- 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.
FRONTAL:
- synchronised (awake with eyes shut) = high frequency, low amplitude waves
- desynchronised (awake with eyes open) = slightly reduced amplitude waves
CENTRAL:
- synchronised (awake with eyes shut) = high frequency, high amplitude waves
- desynchronised (awake with eyes open) = high frequency, low amplitude waves
OCCIPITAL:
- 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?
Alpha
- occipital lobes
- awake, quiet, eyes shut
Beta
- parietal and frontal lobes
- awake with eyes open
Theta
- parietal and temporal lobes
- children
- concentrating/meditating adults
Delta
- 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
Causes:
- intoxication or undercompliance (~40%)
- metabolic disorders e.g. DKA, hypothermia
- hypoxia (~20%)
- neurological
- trauma
Investigations:
- GCS
- scans
- blood work
- history
- EEG
- 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.
Awake:
- 5-HT and noradrenaline constantly active
- ACh neurones active during novel inputs
Non-REM:
- 5-HT and noradrenaline inactive
- ACh inactive
REM:
- 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)
Restorative
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)
Exception:
- 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
CPAP
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
Autoimmune
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)
