Arousal Systems Flashcards
NTs for Coma to Arousal/Wakefulness
EAA/ACh
NTs for Arousal/wakefullness to awareness
Norepi/5HT
NTs for Awareness to Alertness
Dopamine
What do disruptions of consciousness often arise from>
Smaller lesions in brainstem, midbrain or hypothalamus
Why can’t those in PVS “wake up”?
Their cortical neurons are up to 30mV below threshold (hyperpolarized), so nothing is strong enough to activate the neuron.
Why doesn’t the cortex have intrinsic mechanism for activation
Bc they are too hyperpolarized and must rely on ascending influences.
Describe a coma
Not awake or aware
No sleep/wake cycles
Absent brain wave changes
Describe PVS
EEG shows sleep/wake cycles No awareness reflexive motor response Cannot elicit volitional response Hyperpolarized neurons
Describe minimally conscious state
EEG shows sleep/wake
Responds to simple commands inconsistently and w/ varying correctness due to neural plasticity
Damage to which areas can lead to coma or PVS
Lower brain (pons, midbrain & hypothalamus, diencephalon (especially thalamus))
Where is EAA arousal system
Occupies mid-ventral portion of medulla and midbrain.
Arises from parabrachial nuclei in rostral pons
Parabrachial nuclei (medial, intermediate, and lateral) crucial for arousal/activation
Where is cholinergic arousal system
Associated w/ 2 pontine nuclei (Pedunculopontine tegmental and laterodorsal; PPT/LDT)
Where is noradrenergic arousal system
Locus ceruleus
Where is serotonergic arousal system
Midline raphe nuclei
Where is dopaminergic arousal system
Ventral tegmental area (VTA), substantia nigra pars compactica (SNPC) and medullary periventricular system
Inputs of RAS
All modalities of ascending sensory tracts
Trigeminal tracts
Auditory and visual
How does RAS respond equally well to multiple sensory modalities?
The brain just knows something happened because of CONVERGENCE or loss of modal specificity.
Describe dorsal pathway
Axons go to thalamus, synapse at nonspecific nuclei including the intralaminal nucleus of thalamus, release glutamate at thalamus, axons from thalamocortical neurons release EAA
Describe ventral pathway. Which nuclei output only travel ventrally?
Bypasses thalamus, via basal forebrain and hypothalamus, diffuse from here to all higher levels
Parabrahcial nuclei output travel only w/ ventral pathway
What is the main NT utilized by both parabrachial and RAS neurons?
EAA/Glutamate, regardless of dorsal or ventral pathway to brain.
Substantial # of interneurons releasing GABA in RAS, RAS also has a neuronal population releasing ACh
Inputs and outputs to Cholinergic (PPT/LDT) system
I: Afferents sending collateral w/ convergence resulting in loss of modal specificity.
O: Dorsal and ventral pathway w/ ACh being major NT
What happens if PPT and/or LDT are injured
Results in slow cortical processing resulting in memory loss because making new memories requires repetitive memory circuit activation and this baseline wake/arouse is lost
Often injured in Alzheimers pts.
Inputs to noradrenergic locus ceruleus
- Brainstem nuclei (paragigantocellularis in rostral medulla which receives input from all ascending sensory tracts)
- Perifascicular area of nucleus prepositus (PrH)
- Periaqueductal grey for pain (PAG)
- Hypothalamus, amygdala, cortex
Outputs from LC
Consciousness inputs join dorsal and ventral
Dorsal adrenergic bundle to all areas of higher brain except striatum
unrelated outputs to spinal cord
