Phys - Brain Arousal Systems Flashcards
describe coma
neither awake or aware
- no sleep/wake cycles
- EEG waves normally abnormal
describe persistent vegetative state
physiologically identifiable sleep/wake cycles
- no evidence of awareness
- EEG may or may not be abnormal
(the “arousal/wakefulness” level of consciousness)
describe minimally conscious state
pt has sleep/wake cycles
- reproducible evidence of awareness; ability to respond to simple commands
- limited or absent communication
are disruptions of consciousness usually from damage to cerebral cortex?
it can be, but the damage would have to be massive and bilateral
- more often from smaller lesions in brainstem, midbrain, or hypothalamus
what is the reticular activation system (RAS)?
- what tracts use it?
a type of arousal system that uses EAA
- all ascending sensory tracts send info to the RAS
where is the RAS located
mid-ventral portion of medulla and midbrain
why does the RAS system lose modal specificity?
there is sufficient synaptic convergence of input to the neurons of RAS that it loses specificity
compare the two pathways of the RAS
dorsal: synapses in intralaminar nucleus of thalamus
ventral: goes through basal forebrain and hypothalamus but NOT the thalamus
where are the parabrachial nuclei located
in the pons
what inputs go to the parabrachial nuclei?
similar to RAS; all/most of the sensory inputs in the body
what pathway do the parabrachial nuclei use
ventral pathway (bypass the thalamus)
where in the cortex do the parabrachial nuclei innervate?
diffuse innervation of the entire cortex
what is the major NT utilized by both parabrachial nuclei and RAS
EAA/glutamate
what other NTs does the RAS release?
GABA
Ach
why do the PPT/LDT nuclei lose modal specificity?
they receive so much input that specificity is lost
major NT of the PPT/LDT?
Ach
outputs from the PPT/LDT use what pathway?
the dorsal (through thalamus) and ventral (bypasses thalamus) pathways
damage to the PPT/LDT causes what?
produces severe cognitive deficits that are associated with a generalized slowing of cortical processes
- not coma though
transmission of EAA and Ach will get you to what level of the consciousness hierarchy?
from coma –> arousal/wakefulness (persistent vegetative state)
what type of system is the locus ceruleus
noradrenergic (produces NE)
input from the paragigantocellular nerve in the rostral medulla goes to what brain arousal system, and what kind of info is it
locus ceruleus
- sensory input from all ascending tracts
input from the PAG goes to what brain arousal system
locus ceruleus
compare incoming information in the locus ceruleus to that in the EAA/Ach systems
info going to the locus ceruleus has undergone more neural processing than the sensory inputs received by EAA/Ach systems
describe the pathway of output information from the locus ceruleus
joins axons from RAS/parabrachial/PPT/LDT in the dorsal and ventral pathways to become the dorsal noradrenergic bundle
functions of the locus ceruleus noradrenergic system
startle and alerting responses on EEG
- sleep/wake
- behavioral vigilance
what is the input information to the raphi nucleus
- sensory from spinal cord
- trigeminal sensory nucleus
- PAG (proprioception)
what pathways does output information from raphi nucleus use
dorsal and ventral pathways
mostly ventral
what is the function of the serotonergic (raphi nucleus) brain arousal system
quiet awareness
- mood and affect
- modulation of pain
describe the pathway and NTs from coma to alertness
coma –(EAA/Ach)–> arousal/wakefulness –(NE/5HT)–> awareness –(dopaminergic)–> alertness
what arousal system will get you from awareness to full alertness
dopaminergic (ventral tegmental area)
where is the ventral tegmental area
midbrain
function of dopaminergic input
cognitive function
motor activity
emotion
what pathway does the dopaminergic pathway use
dorsal (goes through thalamus) and ventral (bypasses thalamus)
what causes the oscillations on an EEG
from the thalamus there is a diffuse projection to the entire cortex using EAA as an NT –> EAA interacts with intracortical neurons that release GABA –> creates oscillations on EEG
in a persistent vegetative state, what state are the cortical neurons in
10-30 mV hyperpolarized relative to their threshold
what brain arousal systems are hit in Alzheimer’s
cholinergic (PPT/LDT)
what systems move us from being awake to more generally aware of incoming information
noradrenergic (locus ceruleus) and serotonergic (raphi nucleus)
describe the thalamocortical neurons during sleep and the significance of this
the thalamocortical neurons are hyperpolarized and show occasional bursts (spindle-like discharges)
–> this cuts the cortex off from excitatory influence during sleep
