brain arousal Flashcards
what are the 2 parts of consciousness that con possibly dissociate with brain injury
- arousal (being awake)
2. awareness (conscious perception of environment)
compare consciousness in a coma, persistent vegetative state, and minimally consciousnes state
coma - no arousal [wakefulness] or awareness
vegetative - arousal present [sleep/wake cycles present] no awareness. reflexes present. cortical neurons are hyperpolarized bc insufficient input from RAS/ parabracial EAA to increases cortical excitability
minimal - arousal present [sleep/wake cycle] ; minimal awareness [reproducible evidence of awareness by ability to respond to commands at varying degrees] limited or absent communication present
hierarchy of consciousness
coma–> arousal/wakefullness–> awareness –> alertness
*indiciates different parts of the brain are responsible for different levels , and that higher level excitation is needed for full level of consciousness
what is a more common cause of disruption of consciousness (comatose): cortical damage? brainstem/hypothalamus lesion?
- small lesions on brainstem or hypothalamus
* would need large bilateral cortical disruption to get comatosed
what are the two parts of the EAA that are apart the arousal system ? and where are they located
*crucial to baseline excitation of cortical activity
- reticular activating system (RAS) - mid ventral medulla and brainstem
- parabrachial nuclei -pons (has medial intermediaste and lateral parts)
what input is sent to the reticular formation (RAS)
ALL ascending sensory tracts
trigeminal
auditory
visual
**VAST information sent to reticular formation
why is modal specificity lost at the RAS post-synaptic cell ? What effect does this have?
because of large amounts of convergence of neuronal input
-causes the brain to be aware that something happened, but doesn’t know what happened therefore this is the first step in consciousness to achieve wakefulness
what are the pathways that leave the RAS system and excite the cortex ?
- dorsal
- via (nonspecific) intralmainar nucleus of the thalamus - ventral
- via hypothalamus and basal forebrain **bypass thalamus
what is the difference of the RAS and parabrachial nuclei
RAS
-uses ventral and dorsal pathway for diffuse cortical innervation
par brachial nucles
-uses ONLY ventral pathway for diffuses cortical innervation
what is the major EAA neurotransmitter used by the RAS and parabrahcial nuclei
glutamate
what makes up the cholinergic pathway of the arousal system? how does it excite the cortex? what level of brain activity does it provide?
- peduclopontine tegmental and laterodorsal nuclei (PPT/LDN)
- dorsal and ventral pathway
- USES EAA ACTEYLCHOLINE
- convergence and non-specific modality = baseline cortical excitation
what is the side effect of damage to the pons at the PPT and LDN
- *NOT COMA
- severe cognitive deficits such as slowing of cortical processes
what makes the noradrenergic part of the arousal system? where does it receive its input? what are the output tracts? what are its effect on consciousness
level?
- locus coeruleus (in pons)
- recives sensory via paragigantocellularis, Periaquaductal grey (PAG), higher centers
- uses ascending or descending output tracts
1. ascending = ventral/dorsal pathway with RAS and becomes known as the dorsal noradrenergic bundle
2. descending
-startle/alert on EKG, sleep-wake, behavioral vigilance
what makes the serotinoergic part of the arousal system? where does it receive input ? what are the output tracts? effects on consciousness
level?
-raphe nuclei
-sensory from spinal cord (fine proprioception) ,PAG, trigeminal
-dorsal and ventral paths
-quiet awareness
(other effects = mood and affect and modulation of pain)
what makes the dopaminergic part of the arousal system? effects on consciousness
level?
- ventral tegmental area (VTA)
- causes alertness
