Brain Arousal Systems

Question 1

What are the levels of consciousness from least to most aware?

Answer 1

coma –> persistent vegetative state –> minimally conscious state –> conscious

Question 2

What distinguishes a persistent vegetative state?

Answer 2

physiologically identifiable sleep/wake cycles appear

no evidence of awareness

Question 3

What type of damage causes a coma?

Answer 3

massive and bilateral damage to the cerebral cortices

Question 4

What most often causes disruptions in consciousness?

Answer 4

smaller lesions in brainstem, midbrain, or hypothalamus

Question 5

What was found about the nature of consciouness from studies of people in persistent vegetative state?

Answer 5

see marked loss of neurons in pons and brainstem

shows that brainstem regions were critical for arousing the cortex

cortex has no intrinsic mechanism for activation

Question 6

What are the 5 NTs associated with the arousal systems?

Answer 6

EAA

cholinergic

NE

5-HT

Dopamine

Question 7

What is the RAS?

Answer 7

mid-ventral part of medulla and midbrain

loose collection of neurons and fiber tracts

EAA/glutamate = major NT released at targets outside RAS

a lot of GABAergic neurons that begin and end w/in the RAS

Question 8

What are the 4 main inputs to the RAS?

Answer 8

all ascending sensory tracts

Trigeminal

Auditory

Visual

Question 9

What occurs when an input enters the RAS?

Answer 9

specificity is lost - know that something happened, but don’t know specifically what or what kind of stimulus it is

means that the neurons of the RAS respond equally well to multiple sensory modalities

Question 10

What are the 2 general paths of the RAS outputs?

Answer 10

dorsal: to thalamus –> EAA –> nonspec nuclei

ventral: diffuse and non-specific; bypasses thalamus - travels thru basal forebrain and hypothalamus; most go all the way to cortex without synapsing; use EAA

Question 11

What are the 2 sources of EAA involved in arousal?

Answer 11

Reticular Activating System

Parabrachial Nuclei

Question 12

Where is the parabrachial nuclei?

Answer 12

in the pons

lateral, medial, and intermediate nuclei

Question 13

What are the sensory inputs to the parabrachial nucleus?

Answer 13

similar to those in RAS = a bunch of different types of sensory –> lose modal specificity when they synapse

Question 14

What are the major differences btw parabrachial nucleus and RAS paths?

Answer 14

output of parabrachial nuclei travels exclusively via ventral path, bypassing thalamus –> direct excitation of cortical neurons by EAA

RAS goes via dorsal and ventral paths

interneurons w/ GABA in RAS and Ach neurons in RAS as well

Question 15

What is the role of EAA paths in arousal?

Answer 15

crucial for awareness, but not sufficient to produce normal awarenes

Question 16

What are the cholinergic nuclei involved in arousal?

Answer 16

Peduculopontine tegmental and Laterodorsal nuclei (PPT/LDT)

Question 17

What are the inputs and outputs of the PPT/LDT?

Answer 17

Like the RAS, receives a ton of input that modality-specific info is lost

Outputs are via dorsal and ventral paths used by the RAS

major NT is Ach though!

Question 18

What are the functions of the PPT/LDT centers?

Answer 18

baseline excitation to cortex w/ RAS

if these nuclei alone are damaged –> severe cognitive deficits assoc w/ generalized slowing of cortical processes (alzheimer)

Ach inputs help in steps beyond arousal

Question 19

What is the role of EAA and cholinergic inputs together?

Answer 19

normal arousal and est of sleep/wake cycles requires full fxn of both the EAA and Ach systems

EAA is probably the core

Question 20

Where are NE nuclei?

Answer 20

locus ceruleus = in pons

Question 21

What does the locus ceruleus receive inputs from?

Answer 21

brainstem nuclei, especially the paragigantocellularis = sensory info

PAG - periaqueductal grey

Higher centers, including the cortex

Question 22

What are the outputs of the locus coereuleus?

Answer 22

both ascending and descending

ascending: dorsal and ventral w/ RAS = dorsal noradrenergic bundle

Question 23

What are the functions of the Locus Ceuruleus NE system?

Answer 23

startle and alerting responses on EEG

sleep-wake cycles

behavioral vigilance

Question 24

Where are the serotonergic nuclei?

Answer 24

Raphe nuclei - the more rostral, the more likely it is the project to the cortex

Question 25

What are the inputs to the raphe nuclei?

Answer 25

sensory from spinal cord (esp. those synapsing in gracile and cuneate nuclei)

trigeminal sensory

periaquadeuctal grey (pain control)

Question 26

What are the outputs of the Raphe nuclei?

Answer 26

both dorsal and ventral paths are used

Question 27

What are the functions of the Serotonergic pathways?

Answer 27

mood and affect

modulation of pain

Question 28

Where are the dopaminergic nuclei?

Answer 28

ventral tegmental area (VTA)

substantia nigra (less important)

Question 29

What occurs when thalamic neurons w/ EAA input fire in the cortex?

Answer 29

interact w/ intracortical neurons –> GABA –> oscillations seen on EEG

Question 30

What does LSD do?

Answer 30

serotonin agonist

also MDMA

Question 31

What are the inputs to dopaminergic nuclei?

Answer 31

a lot of sensory info

from higher cortical levels

diffuse, but more processing has occured

Question 32

What are the output paths of the dopaminergic nuclei?

Answer 32

5 outputs from VTA

mesencephalic pathway most important: joins dorsal and ventral paths

Question 33

What are the functions of the dopaminergic system in arousal?

Answer 33

alertness in response to novel stimuli

dopamine agonists can improve cognitive function in some ppl in vegetative states

motor control, emotion

Question 34

Which arousal system doesn’t use the dorsal path at all?

Answer 34

EAA from parabrachial nuclei