Lecture 16: Brain Arousal Systems

Question 1

What’s the hierachy (4 components) of Consciousness?

Answer 1

Coma —> Arousal/Wakefulness —> Awarness —> Alertness

Question 2

Disruptions in consciousness result from what type of lesions; what is the common misconception?

Answer 2

• Smaller, subcortical lesions: brainstem, midbrain, and hypothalamus
• Common misconception that comatose state results from damage to cerebral cortices, but cortex has NO intrinsic mech. for arousal. Requires activation!

Question 3

What are the characteristics of a coma vs. persistent vegetable state?

Answer 3

Coma: neither awake or aware

Persistent Veg: physiologically identifiable sleep/wake cycles, no evidence of awarness

Question 4

What does “modal specifity is lost” refer to in regards to the RAS; how does the RAS respond to multiple sensory modalities?

Answer 4

• There is sufficient synaptic convergence of input to the neurons of the RAS
• So much sensory input going in, the specificity of this information is lost.
• RAS responds equally well to multiple sensory modalities

Question 5

The outputs from the RAS are via 2 pathways, what are they?

Answer 5

1. Dorsal - via the non-specifc nuclei of the thalamus, including intralaminar nucleus of thalamus, then diffuses to cortex
2. Ventral - straight to cortex or through forebrain and hypothalamus then cortex

Question 6

Other than the RAS what is the other subgroup of EAA neurons that are crucial for arousal/cortical activation?

Answer 6

Parabrachial nuclei

Question 7

What is one big difference between the EAAs of RAS and Parabrachial Nuclei?

Answer 7

The outputs of the parabrachial nuclei are exclusively via the Ventral pathway

Question 8

What is the major EAA NT utilized by both the parabrachial and the RAS neurons?

Answer 8

• Glutamate
• Is true for both dorsal and ventral pathways

Question 9

What is the role of the EAA system in arousal?

Answer 9

• Provides a baseline excitation that is crucial to cortical activity

Question 10

What is the Cholinergic contribution to the arousal system?

Answer 10

PPT/LDT nuclei of the Pons

Question 11

The outputs of the cholinergic pathway: PPT/LDT are via which pathway and what is the major NT?

Answer 11

• Via the dorsal and ventral pathways
• Major NT is Acetylcholine!

Question 12

Damage specifically to the PPN/DLT has what affect on brain arousal systems?

Answer 12

• Doesn’t necessarily cause coma
• Does produce severe cognitive deficits, associated w/ generalized slowing of cortical processes

Question 13

What are the 2 components of brain arousal system necessary to get us from coma state to arousal/wakefulness; the NT used by each?

Answer 13

1. EAA: RAS and Parabrachial nuclei - Glutamate
2. Cholinergic: PPT/LDT - Acetylcholine

Question 14

The source of the nonadrenergic NT’s for the arousal system is what?

Answer 14

Locus Coeruleus

Question 15

The ascending output from the Locus Coereuleus travel via?

Answer 15

Dorsal and ventral with the RAS

Question 16

The ascending fibers from the locus coereuleus (dorsal and ventral) become what bundle?

Answer 16

Dorsal noradrenergic bundle

Question 17

What is the function of the Locus Coeruleus, NA (norepinephrine) system in arousal?

Answer 17

• Startle and alerting: responses on the EEG
• Sleep-wake
• Behavioral vigilance

Question 18

The startle and alerting responses on the EEG are an indicator of what system functioning?

Answer 18

Noradrenergic: Locus Coeruleus

Question 19

The serotonergic: Raphe Nuclei, use what path(s) for output in the arousal system?

Answer 19

• Both dorsal and ventral
• Ventral is the predominate path (bypasses thalamus)

Question 20

What is the function of Serotonin from the Raphe nuclie in the arousal system?

Answer 20

• QUIET AWARNESS
• Other (non-RAS activites) include:
• Mood and Affect
• Modulation of pain

Question 21

What NT are necessary to get us from the arousal/wakefulness state to the awarness state?

Answer 21

• NE from noradrenergic: locus coeruleus
• Serotonin from serotonergic: raphe nuclei

Question 22

Also found embedded in the RAS is the VTA, which provides what important NT and what are its functions?

Answer 22

• Dopamine
• Cognitive functions
• Motor activity
• Emotion (pleausre)

Question 23

What part of the arousal system is necessary to get us from awarness to alertness?

Answer 23

Dopaminergic: VTA

Question 24

What is the dorsal pathway of the arousal system, where are the synapses?

Answer 24

• Arousal systems send axons to synapse on non-specific nuclei of thalamus (i.e., intralaminar)
• Axons from thalamus go to cortex

Question 25

What is the ventral pathway of the arousal system, where are the synapses?

Answer 25

• Arousal systems send axons straight to cortex
• Synapse directly on cortical neurons

Question 26

From the intralaminar nucleus of the thalamus there is a diffuse projection to the entire cortex, what is the NT of choice?

Answer 26

Utilizing EAA as the NT

Question 27

The neurons from the thalamus interact with a series of intracortical neurons that release what NT and why is this significant?

Answer 27

• Neurons that release GABA (inhibitory)
• This cycle of EAA (excitation) and GABA (inhibition) produces the oscillations seen in the EEG

Question 28

In a persistent vegetative state the rostral regions of the pons/midbrain/thalamus show neuronal loss exceeding that of the cortex, what is the threshold of excitability like?

Answer 28

Cortical neurons are HYPERPOLARIZED

Question 29

What are the thalamocortical neurons like during sleep and why?

Answer 29

• Are hyperpolarized and show occasional bursts (spindle-like)
• Hyperpolarization cuts the cortex off from the excitatory influence during the deepest levels of sleep