Consciousness Flashcards
What are the 3 components required for normal consciousness?
level of consciousness
state of consciousness
content of consciousness
What do the anatomical structures of consciousness components have together?
reciprocal connections and prolific communication
What is level of consciousness?
What is the anatomical component of level of consciousness?
a continuum – asleep/minimal arousal to awake/aroused
anatomical component: diffuse brainstem structures
What is state of consciousness?
What is the anatomical component of state of consciousness?
responsiveness to stimuli (verbal, pain, etc.)
anatomical component: multiple regions of thalamus
What is content of consciousness?
What is the anatomical component of content of consciousness?
perception, emotion, meaning, memories
anatomical component: widespread regions of cerebral cortex
Level of Consciousness: Reticular Formation
What is the function of reticular formation in consciousness?
required for establishing level of consciousness (asleep to awake)
Level of Consciousness: Reticular Formation
What is the reticular formation
numerous nuclei within brainstem that form a diffuse network of interconnected neurons with ascending and descending projections
Level of Consciousness: Reticular Formation
What type of input does reticular formation receive?
receives and modifies afferent input from all sensory modalities
What is the ascending reticular activating system (ARAS)?
subsystem of reticular formation – ascending pathways to cortex
set of connected nuclei in the brain responsible for regulating wakefulness and sleep-wake transitions
Ascending Reticular Activating System (ARAS)
What does ARAS reticular formation do?
processes afferent sensory info from spinoreticular tract afferents from spinal cord to…
thalamus
aminergic and cholinergic nuclei
medial zone of reticular formation
hypothalamus
Ascending Reticular Activating System (ARAS)
What is afferent sensory info sent to thalamus?
to influence cortical input
Ascending Reticular Activating System (ARAS)
What is afferent sensory info sent to aminergic and cholinergic nuclei?
to influence level of consciousness
Ascending Reticular Activating System (ARAS)
What is afferent sensory info sent to medial zone of reticular formation?
to influence output to spinal cord through medial zone
Ascending Reticular Activating System (ARAS)
What is afferent sensory info sent to hypothalamus?
to influence autonomic output
Ascending Reticular Activating System (ARAS)
What are the neurotransmitters?
norepinephrine, dopamine serotonin, histamine, acetylcholine
Ascending Reticular Activating System (ARAS)
What does the neurotransmitter system do?
modify neuronal processing in widespread CNS areas
What does norepinephrine (NE) do?
allows focus on specific task or sensory input, helps suppress less salient inputs
affects arousal, attention, sleep/wake state
What is norepinephrine (NE) produced by?
locus ceruleus
Where is the locus ceruleus?
located within pons, projecting to thalamus and forebrain
What happens if there’s a lesion in the locus ceruleus?
lesion in locus ceruleus = low level of NE = low level of arousal
What does dopamine do?
responsible for behavioural arousal and waking, promoting locomotor and exploratory behaviours toward positively rewarding stimuli
affects motivation, reward
What are dopaminergic neurons?
collections of neurons in CNS that synthesize the neurotransmitter dopamine
Where are dopaminergic neurons?
in ventral tegmental area (VTA), projecting to prefrontal cortex and limbic structures
What happens if there’s a lesion in the ventral tegmental area (VTA)?
lesion in VTA = less attentive, and indecisive
What does serotonin do?
regulates quiet wakeful state in consciousness
affects aggression, mood, sleep/wake state
- mood – sense of well-being
- sleep – lack of serotonin = insomnia
- anxiety/aggression controlled
Where are serotonin-releasing neurons?
in Raphe nuclei, projecting to thalamus, cortex, and other NT systems in brainstem
What does histamine do?
stimulates wakefulness
What does antihistamine do?
induce drowsiness
Where are histamine-releasing neurons?
from midbrain, projecting to thalamus and cortex
What does acetylcholine do?
increase thalamocortical activation and arousal
Where is acetylcholine?
from neurons in pons, projecting to thalamus and cortex
What does the thalamus do?
determines how responsive you are to your environment
What type of nuclei does the thalamus have?
anatomically and functionally distinct nuclei:
- relay nuclei
- association nuclei
‘other nuclei’ – play critical roles in alertness and attention
- intralaminar nuclei
- thalamic reticular nucleus (TRN)
What is the thalamic reticular nucleus (TRN)?
thin mesh of neurons immediately outside of thalamus
is an interconnected network of GABAergic neurons
What are GABAergic neurons?
produce gamma-Aminobutyric acid (GABA), which is the main inhibitory neurotransmitter in CNS
What does the thalamic reticular nucleus (TRN) have dense reciprocal connections with?
- ARAS
- other thalamic nuclei
- cerebral cortical structures
What does the thalamic reticular nucleus (TRN) do?
‘gatekeeper of consciousness’
coordinates synchronous firing (40 Hz) between cortex and thalamus necessary for consciousness
Content of Consciousness: Cortex
What is the cortex required for?
to establish significance and meaning of consciousness experience
Content of Consciousness: Cortex
What connections does the cortex have with other structures? What structures are they?
synchronous and reciprocal connections with thalamus and other cortical areas
Content of Consciousness: Cortex
What are the important areas of the cortex?
prefrontal and parietal cortical areas
What is the prefrontal cortex?
important association area
What is the function of the prefrontal cortex?
considered to have executive function over consciousness
Why is the prefrontal cortex much more complex than other association areas?
it is involved in our ability to associate self with society and society’s expectations:
- to plan future actions
- to predict
- to be attentive
- to concentration on task
- to discriminate between trivial and important
- to behave appropriately
- these executive mental functions are disrupted in frontal lobe disease
