6. Brain Arousal Systems Flashcards
What are the two parts of consciousness
Arousal (awake)
Awareness (conscious processing)
What is the degree of consciousness in a coma?
neither awake/aware
no sleep/wake cycle & EEG = abnormal
-eye and head motions inconsistent/intermittent = brain stem reflexes
What is the degree of consciousness in the persistent vegetative state?
Where would you see lack of neurons in the brain?
Physiologically identifiable sleep/wake cycle (EEG & physical signs = relax Ms, REM paralysis, slow rolling of eyes)
NO Awareness
-rostal regions of pons, midbrain & thalamus have neuronal loss more than cortex
What does it mean to be minimally conscious?
sleep/wake cycles present
awareness = respond to simple comands (sometimes verbal)
what causes disruption of consciousness
- bilateral/massive damage to cerebal cortices
- MORE OFTEN: smaller lesions in brainstem, midbrain or hypothalamus
how do neurons present in persistent vegetative state/comatose state?
structurely normal!
VERY HYPERPOLARIZED (30 mV) - nothing able to get that neuron to threshold
Both arousal and awareness are required for activation of the cortex, how is this achieved?
cortex cant do it on its on (no intrinsic mechanisms)
= relie of ascending influences (multiple sub-cortical structures) to provide activation for cortex to fxn
What are anancephalic babies able to do even without a cortex?
suckle, turn head in response to noise/light
–> b/c brainstem reflexes
where is the reticular activating system located & what does it look like
- mid ventral portion of medulla & midbrain
= loose connections of neurons & fiber tracts, W/O NUCLEI BUT still have cell bodies
where does the reticular activating system recieve input from?
almost all sensory tracts, including:
trigeminal, auditory & visual
What can/cant the RAS do
CAN: detect something is happening; multiple synapse on same neuron –> respond equally well to multiple sensory modalities
CANNOT: process sensory info
How is modal specificity lost in the RAS?
a lot of synapse converging on neurons- so they know something is happening but cant differentiate what it is
What is the dorsal pathway
axons ascend to nonspecific nuclei of thalamus (including intralaminar nucleus of thalamus)
& release excitatory AAs –> then dorsal path will release axons thru-out cortex
=used by RAS
what is the ventral pathway
axons ascend up to basal forebrain & hypothalamus
(bypass the thalamus!)
release excitatory AA & ventral path then sends axons all over the cortex
=used by RAS and parabrachial nuclei
where are the parabrachial nuclei located
in the pons!
contain medial, intermediate and lateral parts
what is the input for parabrachial nuclei
almost all sensory inputs
what path does the parabrachial nuclei use
ventral only! (bypass thalamus)
What path does the RAS use?
dorsal & ventral paths
what are the major NTs used by both parabrachial & RAS neurons
EAA/glutamate
what other NTs does the RAS release that are not similar to parabrachial nuclei
w/i RAS - interneurons (intrinsic RAS) release GABA
contains population that releases ACh
what provides the baseline excitation important for cortical activity
EAA system
cholenergic arousal system
what is the pedunculopontine tegmental & laterodorsal nuclei?
PPT/LDT nuclei = cholinergic arousal system
What are the inputs and outputs of PPT/LDT nuclei?
input: all sensory input, no specificity or processing
output: ACh - made by pontine nuclei
which arousal systems is associated with alzheimers?
a path from PPT/LDT nuclei & cholinergic systems
-slows processing - impair memory
what happens if you damage only the PPT/LDT?
severe cognitive deficits w/ slow cortical processing
-not coma - bc EAA is still working
what processes are active that cause the difference btn coma & arousal/wakeful state
EAA system & cholinergic system = cause baseline arousal
what are the inputs to locus coereuleus
paragigantocellularis N (rostral medulla) = sensory info
periaqueductal grey = pain infor
higher centers including the cortex
what are the outputs/paths of locus coereuleus
NE via dorsal & ventral path
what is the fxn of locus coereuleus
-beginning of neural processing
= startle/alert responses on EEG
=sleep/wake cycle present
=behavioral vigilance (behavior of paying attn
what is the input/output of raphe nuclei
input - sensory info (spinal cord, fine proprioception, CN V)
output - 5-HT via dorsal & ventral paths
what are the fxns of the raphe nuclei/5-HT
Quiet awareness: note that something is always happening but not really pay attn to one particular thing
Mood & affect
Modulation of pain
what is required for awareness?
NE/5-HT
(PPT/LDT nuclei & raphe nuclei)
what does the ventral tegmental area (VTA) do
provide DA input thats imp for fxning
=cognitive fxn, motor activity & emotion
What takes you from aware to alert?
DA
(Ventral Tegmential Area)
what are thalamocortical neurons?
axons from thalamus from the dorsal pathway
= excitatory (release EAA)
=synapse with intracortical neurons (interneurons)
which pathway is affected in alzheimers?
ventral path
what do intracortical neurons do
= interneuron that releases GABA
==> wave of inhibition after excitation
what is the cause of the waves on the EEG
alternating waves of excitation (EAA release) & inhibition (GABA)
what allows full alertness/focused awareness
DA
what happens when persistent vegetative pts are given L-Dopa
increased cognitive fxn - increase awareness
but not sustained
what happens to thalamocortical neurons during sleep?
hyperpolarized w/ short bursts of AP here & there
