Consciousness Flashcards
What is consciousness?
Processes that enable us to experience the world around us
This is distinct from automatic behaviours that occur in a rather unconscious manner
(Overall very hard to define however)
What structure within the brain is heavily involved in regulating alertness?
Reticular Activating System
What is the reticular formation?
A core of grey matter passing through the midbrain, pons and uppermedulla – it is a polysynaptic network that regulates the activity of the cerebral cortex
What are the sensory inputs to the reticular formation?
Sensory and pain from ascending pathways
Vestibular information from medial vestibular nucleus Visual from superior colliculus
Auditory from inferior colliculus
Olfactory via the median forebrain bundle
The RF modulates cerebral activity via various projections. What are these projections?
Noadrenergic projections from the nucleus coeruleus to the cerebral cortex
Dopaminergic projections from the ventral tegmental area to the cerebral cortex
Cholinergic projections to the thalamus
Raphe nuclei in the midline – main source of serotoninergic projections to the brain and spinal cord
(Cholinergic most important for regulating arousal)
What are the three mechanisms by which these projections regulate the level of arousal?
Excitation of individual thalamic relay nuclei –> activation of cortex
Projections to intralaminar nuclei –> project to all areas of cortex
Projections to reticular nucleus– regulates flow of information through other thalamic nuclei to the cortex
What are the different waveforms seen on an EEG and what levels of arousal do they represent?
Delta (< 4 Hz) – seen in sleep Theta (4-8 Hz) – drowsiness
Alpha (8-13 Hz) – subject relaxed with eyes closed
Beta (13-30 Hz) – mental activity and attention
Gamma range (~40 Hz) – creation of conscious contents in the focus of the mind’s eye, via the recurrent thalamo-cortical feedback
What is a cerebral contusion?
Localised bleeding in the brain (bruise in the brain)
What is a concussion?
Diffuse, widespread, homogenous impairment of brain tissue due to brain trauma
What is acute confusion/delirium and stupor?
Acute confusion and delirium– sustained disturbance of consciousness where mental processes are slowed. Subject may be inattentive, disorientated and having difficulty carrying out simple commands or speaking
Stupor– lack of critical cognitive function and consciousness – only responsive to pain
Damage to the reticular formation can lead to coma. What is a coma?
State of unconsciousness in which the subject cannot be roused even by strong sensory stimuli Different from sleep – metabolic activity of the brain is depressed and there is total amnesia for this period
State some causes of coma.
Metabolic alteration e.g. hypoglycaemia, hypoxia, intoxication
Bilateral lesions in the cerebral hemispheres
Lesions in the thalamus or brainstem
Diffuse axonal injury - white matter tracts damaged by hemisphere movement in injury
Diffuse intracranial - injury, meningitis, SAH, encephalitis, epilepsy, hypoxic brain
Describe how the Glasgow Coma Scale is structured.
Eye opening = 4 possible points
Verbal responses = 5 possible points
Motor responses = 6 possible points
What causes a persistent vegetative state?
Disconnection of the brainstem from the cortex or widespread cortical damage Brainstem is still functioning so reflexes, postural movements and sleep-wake cycle may still be present
What is brain death?
Irreversible coma due to brainstem death, but body kept alive artificially
NOTE: spinal reflexes and some postural movements may be present
