Consciousness Flashcards
Compare Consciousness and Arousal
Consciousness: Awareness of external environment and internal states
Arousal: Emotional state associated with goal-seeking behaviour and avoidance of noxious stimuli
Describe the 2 neural components that to be connected to each other and function normally in order to have Consciousness
Cerebral cortex;
- Where conscious thoughts arise
- Receives many inputs including from Reticular Formation
Reticular formation (especially the reticular activating system);
- Keeps cortex ‘awake’
- Receives many inputs including from Cortex and Sensory Systems
Describe the connection between the Reticular Formation and the Cerebral Cortex
Connected by Reciprocal Excitatory Projections, forming a positive feedback loop
(Positive feedback loops are seen where there is a binary outcome)
What is the Reticular formation?
List 4 output locations
A population of specialised interneurones in the brainstem
- Thalamus-> Cortex
- Hypothalamus-> Cortex
- Basal forebrain nuclei-> Cortex
- Spinal cord (muscle tone regulation)
What is the Reticular Activating System?
Part of the reticular formation devoted to arousal
Neurones that ascend to the cortex to maintain cortical activity
Output from Reticular Formation occurs via 3 major relay nuclei
Compare them
Basal Forebrain Nuclei: Send excitatory cholinergic fibres to cortex
Hypothalamus: Sends excitatory histaminergic fibres to cortex
Thalamus: Sends excitatory glutamatergic fibres to cortex
What tool is most commonly used to asses consciousness?
What are the 3 components this looks at?
Glasgow Coma Scale (GCS)
- Best response in eye opening
- Best motor response
- Best verbal response
Other than the GCS, an EEG can be used to assess consciousness
Describe what an Electroencephalogram measures
Describe the resolution quality
Measured combined activity of thousands of neurones in a particular region of the cortex
Good temporal resolution (can see changes across milliseconds)
Low spatial resolution (not good for localising lesions)
What is Neuronal Synchrony?
When neurones in the brain fire synchronously, such as when deprived of sensory input
List 2 processes that an EEG is good for detecting
- Normal cerebral function
- Neuronal synchrony
What are the stages of sleep?
- Stages 1-4
- REM sleep
What happens in 1 sleep cycle?
How many sleep cycles do we usually go through a night?
We enter progressively deeper stages of sleep, then change to REM sleep
6
(Stage 4 is the deepest stage of non-REM sleep)
When awake, why do you see an EEG become more regular when your eyes close?
No visual sensory input leads to Neuronal Synchrony
Describe the EEG pattern in Stage 1 of sleep
Background Alpha waves + interspersed Theta waves
Describe the EEG pattern in Stage 2/3 of sleep
- Background Theta waves
- Interspersed Sleep Spindles and K-Complexes
(Sleep spindles: High frequency)
(KCs: Low frequency, high amplitude)
What are Sleep Spindles and K-Complexes
Sleep spindles: High frequency bursts from thalamus
K-Complexes: Emergence of ‘Intrinsic rate’ of cortex
Describe the EEG pattern in REM Sleep
Dreaming occurs in this stage
Similar to Beta wave pattern when awake
Describe the neural mechanism of Non-REM Sleep
- Removal of sensory inputs, leads to inhibition of RAS-Cortex Positive Feedback Loop
- Leads to Deactivation of Reticular Activating System, leading to Inhibition of Thalamus
Describe the mechanism leading to REM sleep
- Initiated by neurones in the Pons (appears to be an active process)
- Strong inhibition of thalamus (so difficult to wake patient up)
Describe the effect of REM sleep on Muscle Tone
- Inhibition of LMNs by glycinergic fibres coming from Reticular Formation
(To stop us acting out dreams. Sleepwalking is a disorder where this process doesn’t work properly)
Describe the effect of REM Sleep on Eye movements + other cranial nerve functions
Some can be preserved (Can lead to teeth grinding)
List 2 autonomic effects that work in REM sleep
- Penile erection
- Thermoregulation
What does long term deprivation of REM sleep lead to?
Death
List 3 sleep disorders (not including sleepwalking)
- Insomnia
- Narcolepsy
- Sleep Apnoea
What commonly causes Insomnia?
An underlying psychiatric disorder, such as anxiety or depression
(This is Secondary Insomnia)
What may cause Narcolepsy?
- Mutations in Orexin/ Hypocretin gene
Orexin a transmitter that couples light perception to hypothalamus
What causes Sleep Apnoea?
Causes excessive daytime sleepiness
- Often caused by excessive neck fat
- Compression of airways during sleep-> Frequent waking
List and describe 4 disorders of consciousness
- Brain death (widespread cortical and brainstem damage, flat EEG)
- Coma (“” with various EEG patterns, sleep wave cycle undetectable)
- PVS (widespread cortical damage, various EEG patterns, sleep wave cycle detectable, with spontaneous eye opening)
- Locked in Syndrome (Can be caused by basilar/pontine artery occlusion, eye movements can be preserved, loss of somatic motor functions from the Pons down)
What neurotransmitter is used in the synapse between RAS fibres and the Thalamus, Hypothalamus and Basal Forebrain Nuclei
ACh
Describe the EEG pattern in Stage 4 of sleep
Delta waves (Low frequency, high amplitude)
K complexes in Stage 2/3 are a prelude to delta waves
