Tuesday, 3-29-Mechanisms of arousal: Brain arousal systems (Karius)

Question 1

consciousness is recognized as having these 2 parts:

Answer 1

1) arousal (being awake)

2) awareness (conscious processing of inputs, etc.)

Question 2

___ is defined by having physiologically identifiable sleep/wake cycles and no evidence of awareness

Answer 2

persistent vegetative state

Question 3

___ is defined as having sleep/wake cycles, reproducible evidence of awareness (ability to respond to multiple commands), and limited or absent communication

Answer 3

minimally conscious state

Question 4

___ occupies the “mid-ventral portion” of the medulla and midbrain and is a loose connection of neurons and fiber tracts

Answer 4

RAS

Question 5

All ascending sensory tracts send information to the ___

Answer 5

RAS

As do: trigeminal, auditory, and visual

Question 6

Describe inputs to the RAS and modal specificity:

Answer 6

-There is sufficient synaptic convergence of input to the neurons of the RAS that MODAL SPECIFICITY IS LOST–> all the info. converges on the same neurons, so the brain only knows something happened, NOT WHAT HAPPENED

Question 7

The EAA arousal/activating system is associated with these sources:

Answer 7

RAS and parabrachial nuclei

Question 8

This output pathway from the RAS (EAA) is via the non-specific nuclei of the thalamus including the INTRALAMINAR NUCLEUS OF THE THALAMUS. From there, diffuse pathway to all higher levels

Answer 8

Dorsal pathway

Question 9

This output pathway from the RAS is via the basal forebrain and hypothalamus. From there, diffuse pathway to all higher levels

Answer 9

Ventral pathway

Question 10

This source of EAA is located in the pons are crucial for arousal/activation. The sensory inputs are similar to those seen in the RAS but the outputs are likely exclusively via the ventral pathway with extensive, very diffuse innervation of the entire cortex

Answer 10

Parabrachial nuclei

Question 11

The major NT utilized by both the parabrachial and RAS neurons is ___

Answer 11

EAA/glutamate–> true for both dorsal and ventral pathways

Question 12

Regardless of the path (ventral or dorsal), the ___ system appears to provide a baseline excitation that is crucial to cortical activity

Answer 12

EAA

Question 13

The neurons for the cholinergic arousal system are located in these nuclei of the brain

Answer 13

• Pedunculopontine tegmental nucleus

- Laterodorsal nucleus

Question 14

Outputs from the cholinergic arousal system are via the ___ pathways

Answer 14

dorsal and ventral pathways (used by the RAS)

-But, the major NT is Ach!

Question 15

Regardless of the path (same as EAA using dorsal or ventral), the ___ system also appears to provide a BASELINE excitation that is crucial to cortical activity

Answer 15

cholinergic

Question 16

To get from “Coma —> Arousal/wakefulness”, what 2 arousal systems are necessary?

Answer 16

EAA/Ach

Question 17

The cell bodies of neurons producing norepi (noradrenergic system) are located in the __

Answer 17

Locus ceruleus –> Located in the pons, the MAIN source of norepi in the brain

Question 18

The noradrenergic system receives inputs from ___

Answer 18

paragigantocellularis n. (This is the MAJOR input)

• virtually every locus ceruleus cell responds to stimulation of the paragigantocellularis n.
• also receive input from perifascicular area of nucleus prepositus hypoglossi (PrH) and the caudal midbrain periaqueductal gray (PAG)
• These are all brainstem nuclei
• Also receive inputs from higher structures, i.e., hypothalamus, amygdala (another significant source), and cortex

Question 19

Outputs from the locus ceruleus include:

Answer 19

Both ascending and descending

Question 20

The ___ output pathway from the locus ceruleus uses dorsal and ventral pathways with the RAS

Answer 20

Ascending

Question 21

The ascending bundle (output from the locus ceruleus) is known as the ___ bundle

Answer 21

dorsal noradrenergic

Question 22

What are the functions of the locus ceruleus noradrenergic system?

Answer 22

• STARTLE and ALERTING responses on the EEG
• sleep-wake
• BEHAVIORAL VIGILANCE

Question 23

Where are the cell bodies of the serotonergic arousal system located?

Answer 23

Raphe nuclei

Question 24

What are the inputs to the raphe nuclei (serotonergic)?

Answer 24

Multiple, difficult to decide which ones relate to arousal systems
-The ones that probably matter most: sensory from the SC, particularly ones synapsing in gracile and cuneate nuclei, trigeminal sensory nuclei, periaqueductal grey

Question 25

What are the outputs from the raphe nuclei (serotonergic)?

Answer 25

• Ventral pathway (through the hypothalamus)

- Dorsal pathway (through the thalamus)-this is not as strong as the ventral pathway projection

Question 26

What are serotonergic functions?

Answer 26

-QUIET AWARENESS

Question 27

To get from “Arousal/wakefulness —> Awareness”, which systems are necessary?

Answer 27

• Norepi

- 5-HT

Question 28

What is the main location for the dopaminergic systems?

Answer 28

Ventral tegmental area

Question 29

The ___ (along with the substantia nigra) provides a dopaminergic input that is important to many functions, including: cognitive functions, motor activity, and emotion

Answer 29

Ventral tegmental area

Question 30

To get from “Awareness —> Alertness”, what arousal pathway is activated?

Answer 30

Dopaminergic

Question 31

What are the 2 main output pathways from the dopaminergic system?

Answer 31

-Ventral and dorsal pathway

Question 32

This output pathway sends its axons from the thalamus to the cortex (arousal systems sent axons to the thalamus where they synapsed first)

Answer 32

Dorsal –> Dorsal pathway synapses in the non-specific nuclei of the thalamus

Question 33

This output pathway bypasses the thalamus and synapse directly onto cortical neurons

Answer 33

ventral

Question 34

What are the functions of the dopaminergic arousal system?

Answer 34

• alertness in response to novel stimuli
• motor control
• emotion

Question 35

all axons using the dorsal pathway will travel to the non-specific nuclei of the ___. The neurons of this nucleus that are activated by these diffuse projections will then travel to the cortex. The NT released by these neurons is ___

Answer 35

thalamus

EAA/glutamate

Question 36

In the thalamic arousal system: From the thalamus, there is a diffuse projection to the entire cortex utilizing EAA as the NT. These neurons (with their EAA input) interact with a series of intracortical neurons that release ____, to create oscillations that are seen in the EEG

Answer 36

GABA

Question 37

The ___ system is crucial for increasing general excitability of cortical neurons

Answer 37

RAS/Parabrachial EAA system

Question 38

In a persistent vegetative state, the __ regions of the pons/midbrain/thalamus show neuronal loss that exceeds that of the cortex (cortical neurons are 10-30 mV HYPERPOLARIZED relative to their threshold)

Answer 38

rostral

Question 39

In Alzheimer’s disease, the __ systems are particularly hard hit. Mental processes slow dramatically and memory formation is profoundly impaired

Answer 39

cholinergic

Question 40

During sleep, the thalamocortical neurons are hyperpolarized and show occasional bursts (spindle-like discharges). Explain the reasoning for the hyperpolarization:

Answer 40

Hyperpolarization essentially cuts the cortex off from the excitatory influence during the deepest levels of sleep