Session 8 Consciousness Flashcards
(19 cards)
What is consciousness?
What is arousal?
Related to awareness of external environment and internal states
Arousal is a related concept which is associated with goal-seeking behaviour and avoidance of noxious stimuli
What are the two neural components that consciousness requires to be functioning normally?
What are these two systems connected by?
Cerebral cortex = the site where conscious thought arise
* receives many inputs (including from the reticular formation)
Reticular Formation = the circuitry that keeps the cortex ‘awake’
* received many inputs, including from the cortex and sensory systems
These two are connected by RECIPROCAL EXCITATORY PROJECTIONS forming a positive feedback loop
(Where there is a binary outcome)
What are the three major relay nuclei?
Regarding outputs from the reticular formation to the cortex
Reticular formations sends cholinergic (excitatory) projections to these relays:
- Basal forebrain nuclei - send excitatory cholinergic fibres to cortex
- The hypothalamus - sends excitatory histaminergic fibres to the cortex
- The thalamus - sends excitatory glutamatergic fibres to the cortex
NB: the reticular formation also sends projections down the cord, responsible for maintaining muscle tone
What do we use to clinically assess consciousness?
GCS = Glasgow Coma Scale
GCS
eye opening response’s + scale + suggests what?
Spontaneously eye opening (4) = suggests normal cortical and brainstem function
Response to speech (3) = suggest slightly diminished cortical function but still functioning brainstem
Response to pain (2) = suggests impaired cortical function but brainstem preserves so that reflex opening can occur
No response (1) = suggests severe damage to brainstem +/- cortex
GSC
Motor response (6) + suggests
Obeys commands (6) = suggests normal function with working connections from auditory system to brainstem / cord
Localises to stimuli (5) suggests diminished higher
cortical function but still connections working from
sensory to motor cortex
Withdraws to pain (4) suggests that there is still a
‘physiological’ reflex response to stimuli
Flexor response to pain (3) suggests a lesion above the
level of the red nuclei. This response is still ‘semi-
physiological’
Extensor response to pain (2) suggests a lesion below
the red nuclei. This response is not physiological at all
No response to pain (1) suggests severe damage to
brainstem +/- cortex
GCS
Verbal Response
Oriented in time/place (5) suggests normal cortical function
Confused conversation (4) suggests diminished higher cortical function but language centres are still functioning adequately
Inappropriatewords(3)suggestslanguagecentres have been damaged
Incomprehensible sounds (2) suggests cortical damage with brainstem mediated groans
No response (1) suggests severe damage to brainstem +/- cortex
What does the electroencephalogram measure?
temporal resolution high or low?
Spatial resolution high or low?
What is it good for detecting? 2
Measures the combined activity of thousands of neurones in a particular region of cortex
High temporal resolution, low spatial resolution
Good for detecting:
- neuronal synchrony
= a phenomenon which occurs commonly in the brain during both physiological and pathological processes such as sleep and epilepsy - evidence of normal cerebral function
What are the functions of sleep? 5
- generally unknown!
- energy conservation / repair?
- memory consolidation?
- clearance of extracellular debris?
- ‘resetting’ the CNS?
How many cycles of sleep do we pass through per night?
6 cycles
What is sleep made up of?
4 major stages + REM sleep
Stages of sleep? 6 points
Awake with eyes open
o Beta waves – irregular, 50Hz
Awake with eyes closed
o Alpha waves – regular, 10Hz
Stage 1 sleep
o Background of alpha + interspersed theta waves (theta
at around 5Hz, regular)
Stages 2/3 sleep
o Background of theta + interspersed sleep spindles and
k-complexes:
Sleep spindles are high frequency bursts arising
from the thalamus
K-complexes represent the emergence of the
‘intrinsic rate’ of the cortex
Stage 4 sleep
o Delta waves – regular, 1Hz
Related to k-complexes seen in stages 2/3
REM sleep
o EEG similar to beta waves
o Dreaming occurs in this stage, so similar to the EEG in a conscious patient
Quick summary of sleep stages
awake - eyes open
= beta waves
awake - eyes closed
= alpha waves
stage 1
= alpha + some theta
stage 2/3
= theta + some sleep spindles ad k-complexes
stage 4
= delta waves
REM sleep
= similar to beta waves + DREAMING
What is the neural mechanism of non-REM sleep?
- Deactivation of the reticular activating system (and hence cortex) + inhibition of the thalamus
- this deactivation is facilitated by removal of sensory inputs (fewer positive influences of positive feedback loop)
What occurs in REM sleep?
Initiated by what?
EEG?
Initiated by neurones in the pons (i.e. initiation appears to be an active process)
Similar EEG to when awake with eyes open (beta 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 leads to death
What is insomnia caused by?
underlying psychiatric disorders as opposed to ‘primary’ insomnia
What is narcolepsy caused by?
rare
some cases caused by mutations in the orexin gene
What is orexin?
a peptide transmitter involved in sleep
What is sleep apnoea? Caused by what? What does it cause?
= common condition caused by excess neck fat leading to compression of airways during sleep and frequent waking
* causes excessive daytime sleepiness
