UBC NSCI 311 - Reticular Formation & Consciousness

Midterm 2 Material - Lecture 8

State of consciousness

presence or absence

level of consciousness

quantitative amount

content of consciousness

qualitative and subjective experience

what generates the STATE of consciousness

synchronized signalling between thalamus and cerebral cortex

ascending reticular activating system (ARAS) job

responsible for collaborative activity between reticular formation, thalamus and cortex

what contributes to ascending reticular activating system

numerous nuclei of reticular formation, then funnel rostrally to midbrain

ventral route of ARAS

one pathway that projects to hypothalamus and basal forebrain

dorsal route of ARAS

one pathway that projects to thalamus

what makes diencephalon structure

• relay nuclei

• association nuclei

• intralaminar nuclei

• thalamic reticular nucleus

intralaminar nuclei

• within white matter of internal medullary lamina

• involved in dorsal route of ARAS

• heavily involved in signalling for consciousness

internal medullary lamina/septum

separates medial and lateral groups of thalamic nuclei

driver of thalamus

specific information from cortex

what modulates the thalamus

regulatory input that gates and prioritizes its activity

how is the LEVEL of consciousness assessed

motor and verbal responses

what makes LEVEL of consciousness

projections from reticular formation (ARAS) and connections between thalamus and cortex

structure related to CONTENT of consciousness

cerebral cortex (accessed via thalamus)

what is responsible for the content of consciousness

interaction between environmental factors and endogenous factors

reticular formation

diffuse group of nuclei scattered across tegmentum of entire brainstem

what is the difference between regions of the reticular formation

they perform different specialized specific functions

specialized functions of reticular formation in midbrain

• visual accomodation

• vertical gaze

• consciousness (ARAS)

• pain modulation

specialized functions of reticular formation in pons

• horizontal gaze coordination

• consciousness (ARAS)

• pain modulation

specialized functions of reticular formation in medulla

• respiration

• cardiovascular functions

• pain modulation

function of lateral zone of reticular formation

receives and processes sensory information

function of medial zone of reticular formation

processes motor information

how does sensory information enter the lateral zone

all information from sensory ascending systems via spinoreticular tract

where does lateral zone project to

medial zone and monoaminergic system nuclei

why does lateral zone project to medial zone

modulate motor function

why does lateral zone project to monoaminergic system nuclei

influence level of consciousness

what kind of connections does medial zone have

reciprocal connections with systems of motor control and reticulospinal tracts

reciprocal connections of medial zone

cerebral cortex (via thalamus), cerebellum, basal nuclei

function of reticulospinal tracts from medial zone

maintaining muscle tone

how does muscle tone relate to consciousness

typically reflective of our level of consciousness and arousal

what influences wakefulness

orexin neurons in hypothalamus stimulate nuclei of diffuse brain systems and ARAS

what leads to narcolepsy

degeneration of orexin from hypothalamus influencing diffuse brain systems and ARAS

what influences non-REM sleep

inhibition of diffuse brain systems via preoptic nuclei (hypothalamus) and medullary reticular formation

what can lead to insomnia

degeneration of diffuse brain system inhibition via preoptic nuclei and medullary reticular formation

process for REM sleep

• initiated by neurons in pontine reticular formation

• activate thalamus cholinergic system and eye movement system

• inhibit descending motor pathways

what controls respiratory rate and pattern

circuits in pons and medulla

how is respiration controlled

central pattern generators

how is nucleus solitarius involved in respiration

receives visceral sensory input (chemoreceptors and mechanoreceptors)

where is holding your breath controlled

forebrain

where is altered respiratory rhythms controlled

breathing centers, particularly medulla

where is complete cessation of breathing controlled

breathing centers, particularly medulla

what are diffuse modulating systems

projections that stimulate thalamocortical activity to regulate consciousness, attention, sleep-wake, etc.

common features of diffuse modulating systems

• relatively small number of neurons

• long axons with many branches

• release neurotransmitters into extracellular space to act on other neurons

purpose of serotonergic system and noradrenergic system

regulate cortical activity (arousal) and mood

where does serotoninergic system arise

raphe nuclei

where do serotonergic system and noradrenergic system projections synapse

throughout CNS

where does noradrenergic system arise

locus coeruleus

what is associated with low norepinephrine levels

depression (use monoamine oxidase inhibitors and tricyclic compounds)

what else can be treated (other than depression) by noradrenergic medications

narcolepsy

purpose of dopaminergic system

involuntary movement, emotion and reward/pleasure

where does dopaminergic system arise

midbrain - substantia nigra (movement) and ventral tegmental area (emotion, reward, etc.)

where does dopaminergic system project

striatum and limbic/cortical areas

dopaminergic system projections to striatum do what

control movement

dopaminergic system projections to limbic/cortical areas do what

involved in reward and pleasure, determinant of behaviour

degeneration of dopaminergic pathway to striatum

linked to Parkinson’s disease

implications of addiction of narcotics

they mimic dopamine