Flashcards in Session 10 - Conciousness and its Disturbances Deck (55)
What is the reticular formation?
The reticular formation is a collection of cells in the brainstem, pons and medulla. They receive information both from sensory fibres and from collateral fibres of the ascending tracts.
Give five functions of the reticular system?
o Sleep Regulation
o Motor Control
o Cardiac/Respiratory Control
o Autonomic Functions
o Motivation and Reward
Give two major projections of the reticular formation
o Radiations to the whole of the cerebral cortex
Some via thalamus, some direct
o Projections to and from the Hypothalamus
What is the ascending reticular activating system?
o Formed by projections of the Reticular Formation
o Specific effects throughout the CNS to raise the level of consciousness
o ARAS takes Novel Stimulus and raises the level of consciousness so the higher functions of the brain can determine if it is appropriate to make a response
Give four inputs to the ascending reticular activating system
Olfactory is the weakest input
Give four outputs of the reticular activating system
Some fibres via the Thalamus
Some fibres direct to the Cortex
What is the ARAS's unique sensory effect?
Filters unimportant incoming signals
Why does LSD make everything seem so vibrant?
o ARAS filters incoming signals
Inhibited by LSD, people on LSD report colours are more vibrant. Leads to sensory overload and hallucinations
What is ARAS inhibited by?
hypothalamic sleep centres, alcohol, sleeping pills
Give five reticular formation neurotransmitters
o Noradrenaline (NA)
o Serotonin (5-HT)
o Acetylcholine (Ach)
o Dopamine (DA)
What does the ARAS do when we're awake?
o ARAS takes sensory information and raises arousal levels by stimulating the cortex, both directly and via the Thalamus
o Also inhibits inhibitory neurones of the Thalamus
Sensitises the Thalamus to sensory inputs
What happens to ARAS during slow wave sleep/
o ARAS Ach neurones become quiet
o Inhibition of inhibitory neurones removed
Thalamus no longer sensitised to sensory inputs
o Reduction in sensory information being sent to the Thalamus
o Thalamocortical projections now quiet due to inhibition of the Thalamus
What is the origin of EEG waves?
o Cortex feeds back to its stimulation by the Thalamus
o This electrical activity creates oscillating waves
o Cortex can also feed back and activate the ARAS if needed
E.g. if not appropriate to fall asleep (driving etc.)
Anxiety and stress can also stimulate the ARAS preventing sleep
What is EEG?
The algebraic sum of the electrical activity (both excitatory and inhibitory) of neurones, measured from the scalp via electrodes
When does a desynchronised pattern occur on an EEG?
Patient is awake with eyes open, brain is highly active
o High amounts of electrical activity, all travelling in different directions
o Activity cancels each other out, so amplitude is very small
o Frequency very high as activity is high
When does a synchronised pattern occur on EEG?
Patient is awake with eyes shut. Large amplitude waves can be seen in the Occipital Lobe, where the Primary Visual Cortex is located.
o No sensory information projecting from Thalamus to Primary Visual Cortex
o Primary Visual Cortex projecting down to the Thalamus to ‘see what’s going on’
Long, large amplitude waves in bursts
Bursts are alpha spindles
o Frontal lobe is still fairly active, as patient is not asleep
What waves occur when we are asleep?
What is amplitude of alpha waves and when do they occur?
What is amplitude of beta waves? When do they occur?
>14Hz (parietal and frontal lobes) awake + eyes open
What is amplitude of theta waves? Where do they occur and when?
Parietal and temporal lobes
Children, emotional adults
What is amplitude of delta waves? When do they occur <3.5Hz
Give four reasons we need sleep
o Energy conservation (Only conserve the energy in a slice of toast…)
o CNS resetting (period of electrical neutrality needed across the brain)
o Memory (Consolidate short term memory into long term memory)
What controls our sleep-wake cycle (two things)
o Reticular formation (See above)
o Hypothalamus Sleep Centres
Inhibits the ARAS to promote sleep
Give two sleep states
Rapid eye movement sleep
What occurs in non-REM sleep?
Neuroendocrine – 95% of hormones released by the Pituitary during non REM sleep
Decreased cerebral blood flow, O2 consumption, body temperature, BP, respiratory rate – BMR reduced
What occurs in REM sleep?
Difficult to disturb
Irregular heart and respiratory rate
Descending inhibition of motor neurones
Reduced by alcohol
What is the EEG like in REM sleep?
“Active brain, inactive body)
EEG as if awake (Paradoxical)
EEG waves spread from pons to thalamus then occipital lobe
What two fibres are inactive and what type of fibres are active in REM sleep?
In REM sleep noradrenergic and serotonergic fibres are quiet, but Acetylcholine Fibres are fully active and stimulate the brain. It is thought this is to do with processing information and memories.
What happens when we wake up for REM sleep?
When we wake up the Hypothalamus stops inhibition of the ARAS, allowing Noradrenergic fibres to fire and allow the Thalamus to stimulate the cortex.