Introduction to 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
What structure within the brain is heavily involved in regulatingalertness?
Reticular Activating System
What is the reticular formation?
A core of grey matter passing through the midbrain, pons and upper medulla – it is a poly-synaptic network that regulates the activity of the cerebral cortex
What are the sensory inputs to the reticular formation?
recieve info from ALL sensory pathways:
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 (mesocortical tract)
Cholinergic projections to the thalamus - most important role
Raphe nuclei in the midline – main source of serotoninergic projections to the brain and spinal cord
Which of these projections (from RF- NA, DA, Ach or 5-HT) is most important in regulating the level of arousal?
Cholinergic projections
What are the three mechanisms by which these projections (cholinergic to thalamus from RF) 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 (dreaming? don’t really need to know about gamma)
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
Describe how the Glasgow Coma Scale is structured.
Eye opening = /4 (none-spontaneous)
Verbal responses = /5 (none-oriented speech)
Motor responses = /6 (none-obeys commands)
1 is lowest score for each section, so 3 is overall lowest score
What causes a persistent vegetative state?
irreversible coma due to 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
