Neurology 17 - Consciousness Flashcards
List the structures involved in regulating the level of arousal
- Reticular formation
- Polysynaptic network in the core of the midbrain, pons and upper medulla
List the functions of the reticular formation
- Control of alertness
- Centres which regulate cardiovascular, respiratory, bladder and motor patterns
Which sensory pathways does the reticular formation receive information from?
- Touch and pain from ascending tracts
- Vestibular from medial vestibular nucleus
- Auditory from inferior colliculus
- Visual from superior colliculs
- Olfactory via medial forebrain bundle
List the ways the reticular formation modulates cerebral activity
- Locus coeruleus (noradrenergic neurons - pons)
- Ventral tegmental nucleus (dopaminergic neurons - midbrain)
- Cholinergic neurons (project to thalamus)
- Raphe nuclei (in the midline, main source of serotonergic projections to the brain and spinal cord
Which neurons are most important for regulating the level of arousal?
- Cholinergic neurons
- Increase the level of activity in the cerebral cortex via the thalamus
List the three mechanisms of the cholinergic projections of the RAS regulating sleep
- Cholinergic projections excite individual thalamic relay nuclei leading to activation of cortex
- Cholinergic projections to intralaminar nuclei, which in turn project to all areas of cortex
- Cholinergic projections to reticular nucleus, which regulates flow of information through other thalamic nuclei to cortex
What is the function of the tuberomammilary nucleus?
- Histaminergic
- In the hypothalamus
- Projects widely to the cortex, involved in maintaining an awake state
How to the levels of activity in the reticular activating system compare with awakeness?
- Always some activity
- Level correlates with alertness
- Reduced activity results in sleep
How is the level of arousal measured?
- Seen as a change of waveform in EEG (records activity from the cerebral cortex)
- Different basic rhythms are defined by frequency
List the 4 basic rhythms of arousal and their frequency
- Delta (0.5-4Hz) present during sleep
- Theta (4-8Hz) associated with drowsiness
- Alpha (8-13Hz) subject relaxed with eyes closed
- Beta (13-30Hz) indicates mental activity and attention
What do altered states of consciousness refer to?
- The level of consciousness
- Not the contents
List the altered states of consciousness
- Concussion or contusion (temporary loss, only lasts a few minutes)
- Confusion (sustained disturbance of consciousness)
- Stupor
- Coma (cannot be roused by even strong sensory stimuli)
Compare confusion and stupor
- In confusion mental processes are slowerd
- Confusion results in people being inattentive, disoriented, or having difficulty carrying out simple commands or speaking
- Stupor can only be roused by strong sensory stimuli
What is the Glasgow Coma Scale?
- International standard measure of level of consciousness
- Eyes (4 - none, pain, speech, spontaneous)
- Verbal responses (5 - no verbal response, incomprehensible, inappropriate words, disoriented speech, oriented speech)
- Motor response (6 - extensor/flexor pain response, withdrawal from pain, localisation of pain, obeys commands)
What can coma be produced by?
Metabolic causes
- Drug overdose
- Hypoglycaemia
- Diabetes
- Hypercalcaemia
Diffuse intracranial
- Head injury
- Meningitis
- SAH
- Encephalitis
- Epilepsy
- Hypoxic brain injury
Hemisphere lesion (cerebral infarct, haemorrhage or tumour)
Brainstem (infarct, tumour, haemorrhage)
What is brain death?
- Irreversible coma due to brainstem death
- Body kept alive artificially
- Decision to cease treatment depends on brainstem reflexes and response to hypercapnia
- EEG is not diagnostic
- Spinal reflexes and postural movements may still be present
What is a persistent vegetative state?
- Irreversible coma due to disconnection of the cortex from the brainstem, or widespread disease in the cerebral hemispheres
- Brainstem still functioning, so reflexes, postural movements and sleep-wake cycle may still be present
How are vegetative state patients differed from those in a coma?
- Vegetative state patients can be aroused
- Both groups are believed to be unconscious
What are the neural correlates of consciousness?
- Minimal brain activity sufficient to produce conscious awareness of information
- Primarily localised to a posterior cotical hot zone that includes sensory areas
Give examples of how brain lesions can alter the contents of consciousness
- Lesions to the extra-striae cortex can eliminate awareness of colour (achromatopsia)
- Parietal lesions may lead to lack of awareness for stimuli in the contralateral visual field relative to the side of the brain lesion (neglect)
Are perceptual brain regions necessary for conscious experience?
- Debated
- Patients with damage to the primary visual cortex report being unaware but can still display non-conscious visual processing)
Define consciousness
- The state of being aware of and responsive to ones surroundings
- Consists of level, content and self
Explain the mechanisms of consciousness
- High integration (neurones working together, multiple brain regions are involved)
- High differentiation (different brain regions doing a range of things)
Describe minimally conscious state
- Severely altered consciousness
- Minimal but clearly discernible behavioural evidence of self- or environmental awareness is demonstrated
- Eg. dementia
