Consciousness Flashcards
What is consciousness?
- Related to awareness of external and internal states
- Arousal is a related concept which is associated with goal-seeking behaviour and avoidance of noxious stimuli
Which two neural components are required for consciousness?
- Cerebral cortex
- Reticular formation
What is the function of the cerebral cortex in consciousness?
- The site where conscious thoughts arise
- Receives many inputs, including from the reticular formation
What is the function of the reticular formation in consciousness?
- This is the circuitry that keeps the cortex awake
- Receives many inputs from the cortex and sensory systems
How do the cortex and reticular formation work together?
- Connected by reciprocal excitatory projections, forming a positive feedback loop
- Positive feedback loops are seen where there is a binary outcome
What are the outputs from the reticular formation to the cortex?
- Occurs via three major relay nuclei
- Reticular formation sends cholinergic (excitatory) projections to these relays
What are the different major relay nuclei of the reticular formation?
- Basal forebrain nuclei
- Hypothalamus
- Thalamus
What do the basal forebrain nuclei do?
- Send excitatory cholinergic fibres to cortex
- Think sedative side effects of anticholinergics
What does the hypothalamus do?
- Send excitatory histaminergic fibres to the cortex
- Think sedative side effects of antihistamines
What does the thalamus do?
- Sends excitatory glutamatergic fibres to the cortex
What is the motor function of the reticular formation?
- Sends projections down the cord, responsible for maintaining muscle tone
How is consciousness clinically assessed?
- GCS
What are the components of the GCS?
- Eye opening
- Motor response
- Verbal response
How is eye opening assessed in the GCS?
- Spontaneous eye opening suggests normal cortical and brainstem function
- Response to speech suggests slightly diminished cortical function but still functioning brainstem
- Response to pain suggests impaired cortical function but brainstem preserved so that reflex opening can occur
- No response suggests severe damage to brainstem +/- cortex
How is motor response assessed in the GCS?
- Obeys commands (6)
- Localises to stimuli (5)
- Withdraws to pain (4)
- Flexor response to pain (3)
- Extensor response to pain suggests a lesion below the red nuclei (not physiological at all)
- No response to pain suggests severe damage to brainstem +/- cortex
What does a patient obeying a motor command suggest?
- Normal function with working connections from auditory system to brainstem/cord
What does a patient localising to stimuli suggest?
- Diminished higher cortical function but still connections working from sensory to motor cortex
What does a patient withdrawing to pain suggest?
- There is still a physiological reflex response to stimuli
What does a patient flexing in response to pain suggest?
- Suggests a lesion above the level of the red nuclei (semi-physiological)
What does a patient extending in response to pain suggest?
- Severe damage to the brainstem +/- cortex
How is verbal response assessed by the GCS?
- Oriented in time/place (5) - normal cortical function
- Confused conversation (4) - diminished higher cortical function but language centres are still functioning adequately
- Inappropriate words (3) - language centres have been damaged
- Incomprehensible sounds (2) - cortical damage with brainstem mediated groans
- No response (1) - severe damage to brainstem +/- cortex
What does the electroencephalogram measure?
- The combined activity of thousands of neurones in a particular region of the cortex
- High temporal resolution, low spatial resolution
What is the electroencephalogram good for?
- Detecting neuronal synchrony and evidence of normal cerebral function
What is neuronal synchrony?
- A phenomenon which occurs commonly in the brain during both physiological and pathological processes such as sleep and epilepsy
What are the functions of sleep?
- Generally unknown
- Energy conservation/repair
- Memory consolidation
- Clearance of extracellular debris
- Resetting of the CNS
How many sleep cycles do we typically pass through each night?
- 6
What are the stages of sleep?
- 4 major stages and REM sleep
What happens on an EEG when a person is awake with their eyes open?
- Beta waves - irregular, 50 Hz
What happens on an EEG when a person is awake with their eyes closed?
- Alpha waves - regular, 10 Hz
What happens on an EEG when a person is in stage 1 sleep?
- Background of alpha and interspersed theta waves
- At around 5 Hz
What happens on an EEG when a person is in stage 2/3 sleep?
- Background of theta and interspersed sleep spindles and k-complexes
What are sleep spindles?
- High frequency bursts arising from the thalamus
What are k complexes?
- Represent the emergence of the intrinsic rate of the cortex
What happens on an EEG when a person is in stage 4 sleep?
- Delta waves - regular 1 Hz
- Related to k-complexes seen in stages 2/3
What happens on an EEG when a person is in REM sleep?
- Initiated by neurones in the pons
- EEG is similar to when person is awake with eyes open
What happens to the body during REM sleep?
- Difficult to rouse due to strong thalamic inhibition
- Decreased muscle tone due to glycinergic inhibition of LMNs
- Eye movements and some other cranial nerve functions can be preserved
- Autonomic effects are seen
- Essential for life
What are some different types of sleep disorder?
- Insomnia - commonly caused by underlying psychiatric disorder as opposed to primary insomnia
- Narcolepsy - rare disorder
- Sleep apnoea - causes excessive daytime sleepiness
What causes narcolepsy?
- Some cases are caused by mutations in the orexin gene
- Orexin is a peptide
What causes sleep apnoea?
- Excess neck fat leading to compression of airways during sleep and frequent waking
