Brain Arousal Systems Flashcards
Consciouness is composed of which two parts?
- Arousal (being awake)
- Awareness (Conscious processing of inputs, etc.)
Define:
- Coma
- Persistent Vegetative State
- Minimally Conscious State
- Coma: Neither awake or aware
- PVS: Physiologically identifiable sleep/wake cycles appear; NO evidence of awareness; NON-responsive to STIMULI
- MCS: Sleep/Wake Cycles; Reproducible evidence of awareness - ability to respond to simple commands; Limited or absent communication; Responsive to STIMULI!
Where in the brain are lesions going to more often present with disruptions of consciousness?
Lower down in the brain @ the Brainstem, Midbrain, or hypothalamus
Explain the final piece of information that was found in research with Patients in Persistent Vegetative States in relation to their threshold.
Cortical Neurons are up to 30 mV BELOW threshold than under normal conditions! (Massively HYPERPOLARIZED)
Which portion of the brain will be used to excite the cortex in order to bring our mind to Full Consciousness?
Brainstem
List the various regions that are responsible for AROUSAL.
- Excitatory Amino Acids
- Reticular Activating System (RAS)
- Parabrachial Nuclei - Cholinergic: Pedunculopontin tegmental and Laterodorsal nuclei (PPT/LDT)
- Noradrenergic: Locus Ceruleus
- Seroteonergic: Raphe Nuclei
- Dopaminergic: Ventral Tegmental Area
*** All located in the Midbrain area!
Describe the Reticular Activating System.
What are the 2 pathways that are going to be sent out of the Reticular Activating System?
Loose Collection of Neuron and Fiber Tracts located in the “Mid-Ventral Portion” of the Medulla and Midbrain
*** Recieve input from:
- ALL ascending sensory tracts
- Trigeminal
- Auditory
- Visual
*** RAS is not involved in processing the information; instead, it has “Lost Modal Specifity”.
*** Second Pathway DOES NOT go through the Thalamus
Describe the Parabrachial Nuclei.
What is the output pathway?
Which EAAs are likely released?
Located in the PONS (medial, intermediate, and lateral are crucial for arousal and activation of cortex)
- Contain Excitatory Amino Acids (EAA) - Glutamate!
- Their output are likely EXCLUSIVELY the VENTRAL pathway; which will innervate the entire cortex.
Describe the Pedunculopontine tegmental and Laterodorsal Nuclei (PPT/LDT). What are the outputs? Which neurotransmitter is going to be used?
Located in the PONS
- Also RECIEVE ALL sensory information coming in!
- OUTPUTS: BOTH the Dorsal and Ventral Pathways are used.
- ACHETYLCHOLINE is going to be the neurotransmitter used
*** Damage specifically to the PPN/DLT doesn’t necessarily cause coma, but does produce severe cognitive deficits that are associated with a generalized SLOWING of cortical processes.
Which step will you get to in the Alterness cycle when you have INTACT EAA/Ach function?
You will be in a Persistent Vegetative State with ONLY these two functions intact.
*** Need more inputs in order to take you to the NEXT LEVEL!
Describe the Locus Coereuleus (Nor-Adrenergic System).
Inputs / Outputs?
What do the ascending fibers from this group of cells become?
What are the functions of the Locus Coereuleus?
Located in the Upper Pons
- Recieves SENSORY input from EVERYTHING but it is a little more PROCESSED!
- *INPUTS:**
- Paragigantocellularis n (rostral Medulla) gives sensory information
- PAG
- Higher Centers including the Cortex
- *Outputs:**
- Ascending: Dorsal & Ventral with the RAS
**** The ascending fibers from this group of cells become the dorsal noradrenergic bundle.
*** Function of this system is dependent on the RAS and Parabrachial systems because they are going to send information to the cortex and the cortex will send it to the LOCUS COEREULEUS
- STARTLE & ALERTING response on the EEG (electroencephalogram)
- Sleep-Wake
- Behavior Vigilance (aware that something is going on)
Describe the Raphe Nuclei (Serotonergic) processing.
Works similar to the Locus Coereuleus. Have to have Ach and EAAs present in order to get information to the cortex and back!
INPUTS: Sensory from spinal cord (fine proprioception), trigeminal nerve, and PAG (involved in pain)
OUTPUTS: BOTH Dorsal and Ventral Pathways are used!
Describe the function of the Serotonergic (Raphe Nuclei).
- Quiet Awareness: Not focused on one specific thing but you know what is going on around you.
- Mood and Affect
- Modulation of Pain
How do we move from the Arousal/Wakefulness state to the Awareness State?
5HT = Serotonin
NE = Noradrenergic
Describe the Dopaminergic Inputs from the Ventral Tegmental Area.
- Sensory Information that has gone to the Cortex and telling the Brain to pay attention to this specific thing!
How do we make the move from Awareness to Alterness?
If axons are traveling in the Dorsal Pathway, explain what is happening in relation to where things synapse and where they are going.
Dorsal Pathway Synapses in the non-specific nuclei of the thalamus (i.e Intralaminar Nuclei)
*** Thalamocortical Neurons will synapse with INTRACORTICAL neurons and will release GABA
If axons are traveling in the Ventral Pathway, explain what is happening in relation to where things synapse and where they are going.
