Brain Arousal Systems (Karius) Flashcards
(44 cards)
Components of consciousness:
Arousal (being awake)
Awareness (being actually aware)
Brain injury can dissociate these components
Coma:
Vegetative state:
Minimally conscious state:
- neither awake nor aware
- Has sleep/wake cycles but no evidence of awareness
- clear sleep/wake cycles, reproducible awareness by ability to respond to simple commands, limited or absent communication
Most people in coma or vegetative state show ….
How do cortical neurons behave in these patients?
Damage to lower levels of the brain (midbrain, brainstem and hypothalamus). Used to be thought that to lose awareness means damage to the cortex.
-Cortex neurons are usually alive, but hyperpolarized (not firing), about 30 mV below threshold. Signals not strong enough to generate AP.
What does the hierarchy of consciousness suggest about its physiological basis?
Different levels (coma, vegetative etc.) are a result of different levels of cortical excitation
Cortex and consciousness
Cortex cannot excite itself. It relies on ascending signals to get activation.
Brainstem arousal systems:
5 neurotransmitter systems
Excitatory amino acid system Cholinergic system Norepinephrine Serotonin Dopamine
Excitatory amino acid system:
Core of the arousal systems
Associated with RAS within the medulla
Arise from parabrachial nuclei in the rostral pons
Cholinergic system:
What nuclei?
Ach and EAA are critical for producing arousal
Associated with pedunculopontine tegmental and laterodorsal tegmental nuclei
Norepinephrine system:
What nuclei?
Associated with locus ceruleus
Moves us from arousal to awareness (along with serotonin)
Serotonin system:
What nuclei?
Associated with midline raphe nuclei
Moves us from arousal to awareness (alogn with Norepi)
Dopamine system:
What nuclei?
Associated with ventral tegmental area
Moves us from awareness to focused alertness
Which systems are required to get from Coma to vegetative state?
Excitatory amino acids
Acetylcholine
Excitatory amino acids:
RAS (reticular activating system)
Where is it?
What type of input does it receive?
- Mid ventral portion of the medulla and midbrain
- Receives all ascending sensory and trigeminal tracts, auditory and visual info
Characteristics of RAS input
Synapses converge. modal specificity is lost since there are so many sensory inputs coming in. We know there is some sensory input but don’t know what kind specifically. Not part of processing (does not tell you what you’re feeling etc.), but tells you there’s some input there.
Describe the dorsal pathway from RAS:
Axons from the RAS go to thalamus > synapse at non-specific nuclei in the thalamus
EAA/glutamate released in the thalamus > diffuse pathways to all higher levels (sends neurons broadly over the cortex)
Describe the ventral pathway from RAS:
Nonspecific pathway and bypasses the thalamus > basal forebrain and hypothalamus > diffuse pathways to all higher levels (sends neurons broadly over the cortex)
Parabrachial nuclei:
What areas of the brain?
Mostly the lateral subnucleus, but also medial and intermediate nucleus
Sensory info comes in similar to how it comes in via RAS (all sensory modalities, modal specificity is also lost)
RAS vs parabrachial nuclei?
Parabrachial travels only on ventral pathway which bypasses the thalamus and synapses to the hypothalamus instead
Both use EAA/glutamate
Role of the EAA/glutamatergic pathways:
Core of the arousal pathways
Provides baseline excitation of the cortex that is necessary to producing arousal
This is NOT sufficient to produce awareness
Which system is crucial in getting from coma to vegetative state?
Which nuclei do these neurons originate from?
What neurotransmitter is important for the cholinergic system?
Cholinergic arousal system (needs EAA to be working too)
Pedunculopontine tegmental (PPT) and laterodorsal tegmental (LDT) nuclei
Acetylcholine (duH)
Inputs to the PPT/LDT…
Output pathways…
Similar to RAS. All afferents send info here and modal specificity is also lost
Uses both ventral and dorsal pathways just like RAS
What disease damages the cholinergic system?
Alzheimer’s
Function of the Cholinergic arousal system:
Also provide baseline excitation to the cortex. Necessary but NOT sufficient for arousal
Damage to the cholinergic arousal system
Damage to the PPT/LDT nuclei result in cognitive deficits that slow cortical processes (e.g. resulting in Alzheimer’s memory loss since it requires repetitive activation of the memory circuits)
