8.2 control of consciousness Flashcards
what is consciousness?
awareness of external environment and internal states
where do conscious thoughts arise from?
the cerebral cortex
why would anti histamines make you feel drowsy?
histmamine stimulates the cerebral cortex
if inhibited, = less stimulation = feel drowsy
what Is the reticular formation and what is the role of the reticular formation?
it is a population of specialised interneurones in the brainstem
keeps the cortex awake
outputs from reticular formation send cholinergic (excitatory) projections to cortex
what connects the cortex and reticular formation, and what is the importance of this connection?
connected by reciprocal excitatory projections, forming a positive feedback loop
consciousness requires the cortex and reticular formation to be functioning normally and connected
how is the reticular formation connected to the cortex?
- basal forebrain send excitatory cholinergic fibres to cortex
- hypothalamus sends excitatory histaminergic fibres to cortex
- thalamus sends excitatory glutamatergic fibres to the cortex
how does the reticular formation aid muscle tone?
it sends projections down the spinal chord, responsible for maintaining muscle tone
what can be used clinically asses consciousness?
the Glasgow coma scale (GCS) assesses - eye movements - motor response - verbal response
what is the role of an electroencephalogram?
measures combined activity of thousands f neurones in a particular region of the crtex
high temporal resolution, low spatial resolution
good for detecting neuronal synchrony and evidence of normal cerebellar function
what are the functions of sleep?
- generally unknown
- energy conservation/ repair
- memory consolidation
- clearance of extracellular debris
- resetting of the CNS
what are the stages of sleeping?
- awake with eyes open (high frequency irregular)
- awake with eyes closed (high frequency. regular)
- stage 1 sleep (background theta and interspersed sleep spindles that are high frequency)
- stage 2/3 sleep (background theta and interspersed sleep spindles)
- stage 4 - delta waves, regular
- REM sleep (dreaming occurs in this stage, so similar to the EEG in a conscious patient)
what is the neural mechanism of non REM sleep?
- complex
- deactivation of the reticular activating system (and hence cortex) + inhibition of the thalamus
- facilitated by removal of sensory inputs (fewer positive influences on positive feedback loop)
what is the n rural mechanism of REM sleep?
- initiated by neurones in the pons i.e imitation appears to be an active process
- similar EEG to when awake with eyes open (B waves) but difficult to rouse due to strong thalamic inhibition
- decreased muscle tone due to glycinergic inhibition of lower motor neurones
- eye movements and some other cranial nerve functions can be preserved e.g teeth grinding
- autonomic effects are seen e.g penile erection, loss of thermoregulation
- essential for life (long term deprivation = death)
what is insomnia?
unable to sleep
commonly caused by underlying psychiatric disorders as opposed to primary insomnia
what is narcolepsy?
rare disorder
fall asleep randomly
some causes are caused by mutations in the orexin gene
(Orexin is a peptide transmitter involved in sleep)
what is sleep apnoea?
common condition, often caused by excess neck fat leading to compression of airways during sleep and frequent waking
causes excessive daytime sleepiness
what do the different GCS gradings for eye opening suggest, 1-4?
1 = no response. damage to brainstem and maybe cortex,
2 = response to pain. impaired cortical function but brainstem is preserved so that reflex opening can occur.
3 = response to speech suggests slightly diminished cortical function but still functioning brainstem.
4 = spontaneous eye opening suggests normal cortical and brainstem function
what do the different GCS gradings for motor response suggest, 1-6?
1 = no response to pain suggests severe brainstem damage
2 = extensor response to pain suggests a lesion below the red nuclei. this response isn’t psychological at all.
3 = flexor response to pain suggests a lesion above the level of the red nuclei. This response is still semi-physiological.
4 = withdraws to pain suggests a physiological reflex response to stimuli
5 = localises to stimuli suggests diminished higher cortical function, but still connections working from sensory to motor cortex.
6 = obeys command. suggests normal function working connections from auditory system to brainstem/cord.
what do the different GCS gradings for verbal response indicate, 1-5?
1 = no response. suggests severe brainstem damage and maybe the cortex.
2 = incomprehensible sounds suggests cortical damage with brainstem mediated groans
3 = inappropriate words suggests language centres have been damaged
4 = confused conversation suggests diminished higher cortical function but language centres are still functioning adequately
5 = orientated in the/place suggests normal cortical function
