Flashcards in Session 10 - Conciousness and its Disturbances Deck (55)
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1
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.
2
Give five functions of the reticular system?
o Sleep Regulation
o Motor Control
o Cardiac/Respiratory Control
o Autonomic Functions
o Motivation and Reward
3
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
4
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
5
Give four inputs to the ascending reticular activating system
Sound
Pain
Visual
Somatosensory
Visceral pain
Olfactory is the weakest input
6
Give four outputs of the reticular activating system
Motor
Autonomic
Some fibres via the Thalamus
Some fibres direct to the Cortex
7
What is the ARAS's unique sensory effect?
Filters unimportant incoming signals
8
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
9
What is ARAS inhibited by?
hypothalamic sleep centres, alcohol, sleeping pills
10
Give five reticular formation neurotransmitters
o Noradrenaline (NA)
Depression
o Serotonin (5-HT)
Depression
o Acetylcholine (Ach)
Alzheimer’s
o Dopamine (DA)
Parkinson’s, Schizophrenia
11
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
12
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
13
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
14
What is EEG?
The algebraic sum of the electrical activity (both excitatory and inhibitory) of neurones, measured from the scalp via electrodes
15
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
16
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
Alpha waves
Bursts are alpha spindles
o Frontal lobe is still fairly active, as patient is not asleep
17
What waves occur when we are asleep?
Delta
18
What is amplitude of alpha waves and when do they occur?
8-13Hz
19
What is amplitude of beta waves? When do they occur?
>14Hz (parietal and frontal lobes) awake + eyes open
20
What is amplitude of theta waves? Where do they occur and when?
4-7Hz
Parietal and temporal lobes
Children, emotional adults
21
What is amplitude of delta waves? When do they occur <3.5Hz
3.5Hz
Deep sleep
22
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)
o Homeostasis
23
What controls our sleep-wake cycle (two things)
o Reticular formation (See above)
o Hypothalamus Sleep Centres
Inhibits the ARAS to promote sleep
24
Give two sleep states
Non-REM sleep
Rapid eye movement sleep
25
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
26
What occurs in REM sleep?
Dreaming
Difficult to disturb
Irregular heart and respiratory rate
Increased BMR
Descending inhibition of motor neurones
Penile erection
Reduced by alcohol
27
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
28
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.
29
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.
30
