Reticular Formation Flashcards
What is the reticular formation?
- Central core of nuclei embedded in the tegmentum of the brainstem
- Runs the length of the brainstem
- Continuous with diencephalon nuclei and the intermediate zone of the spinal cord
Describe the structure and function of the rostral reticular formation
- Consists of nuclei in the midbrain, upper pons, diencephalic nuclei
- Maintains alert conscious state in the forebrain
Describe the structure and function of the caudal reticular formation
- Consists of nuclei in the pons, medulla, cranial nerve nuclei, and spinal cord
- Carries out important motor, reflex, and autonomic functions
What are the three levels of consciousness?
Alertness
Attention
Awareness
Describe pathway of the pontomesencephalic reticular formation
- Will receive inputs about pain from sensory pathways, about cognition from the association cortex , and about emotion from the limbic system
- Will send output to the thalamus, hypothalamus, and basal forebrain
- Information transmitted via glutamate
- Function: alertness
- Bilateral lesions can cause a coma
Describe the pathway of the basal forebrain that communicates via acetylcholine
- Basal forebrain sends acetylcholine to the cerebral cortex and hippocampus
- Effects attention, memory, and learning
Describe the pathway of the pontomesenphalic region that communicates via acetylcholine
- Pontomesenpahlic region sends acetylcholine to the thalamus and then the cortex to influence arousal
- Also sends Ach to cerebellum, basal ganglia, and brainstem to influence locomotion
Describe the mesostriatal pathway
Dopamine from SNc and ventral tegmental area is sent to the caudate and the putamen for basal ganglia functions
Describe the mesolimbic pathway
Dopamine from the SNc and ventral tegmental area is sent to limbic structures to influence reward and addiction
Describe the mesocortical pathway
Dopamine from the SNc and ventral tegmental area is sent to the prefrontal cortex to influence working memory and attentional aspects of movement intiation
Describe the norepinephrine pathway in the reticular formation
- Neurons located in the locus ceruleus and lateral tegmental area send norepinephrine to the thalamus (excitatory), cortex (excitatory/inhibitory), and cerebellum, brainstem, spinal cord
- Influences attention, sleep-wake cycles, mood, and sympathetic BP
Describe the serotonin pathway involving the rostral raphe nucleus
- The rostral raphe nucleus sends serotonin to the cortex, basal ganglia, and thalamus
- Plays a role in some psychiatric symptoms
Describe the serotonin pathway involving the caudal raphe nucleus
- The caudal raphe nucleus sends serotonin to the cerebellum, medulla, and spinal cord
- Plays a role in pain modulation, breathing, temperature regulation, and motor control
Describe the histamine pathway in the reticular formation
- Neurons in the posterior hypothalamus send histamine to the thalamus (excitatory), and the cortex (excitatory/inhibitory)
- Helps maintain alert state
Describe the orexin pathway in the reticular formation
- Neurons located in the posterior lateral hypothalamus send orexin to the cortex and all brainstems arousal systems
- Promotes staying awake
Describe the GABA pathway in the reticular formation
- Neurons in the basal forebrain, thalamic reticular nucleus, and anterior hypothalamic ventrolateral preoptic area sends GABA to the cortex, thalamus, brainstem reticular formation, and hypothalamus
- Influences alertness and regulation of sleep
Describe the stages of sleep
- Non-REM: consists of three stages (N1, N2, N3) that get progressively deeper
- REM: low muscle tone, dreaming, EEG is similar to wakeful state
Which neurotransmitters are active during wakefulness?
Acetylcholine, serotonin, norepinephrine, dopamine, and orexin are all rapidly firing
Which neurotransmitters are active during non-REM sleep?
GABA is rapidly firing and serotonin, norepinephrine, and dopamine are slowly firing
Which neurotransmitters are active during REM sleep?
Acetylcholine and GABA are rapidly firing
What is occurring during non-REM sleep?
- VLPO releases GABA
- Posterior hypothalamus is inhibited which decreases orexin, histamine, and glutamate activity
- Brainstem ascending activating system is inhibited which decreases serotonin, norepinephrine, dopamine, and acetylcholine
What is occurring during REM sleep?
- Norepinephrine and serotonin levels decrease which decrease inhibition to brainstem cholinergic neurons and increase release on acetylcholine
- Ach acts on thalamus and cortex to increase arousal
- Ach acts on ponto-geniculo-occipital waves to induce visual imagery of dreams and rapid eye movement
- Ach acts on cells in pontine reticular formation to decrease muscle tone
How does the anterior hypothalamus contribute to sleep?
- Ventral lateral pre-optic area inhibits arousal systems in the posterior hypothalamus and brainstem to promote REM sleep
- Lesion = insomnia, cannot inhibit arousal systems
How does the posterior hypothalamus contribute to sleep?
- Glutamate, histamine, and orexin help maintain alert state
- Lesion = hypersomnia, no alert state
What is narcolepsy?
Abnormal tendency to easily enter REM sleep directly from waking
What are the four classic presentations of narcolepsy?
- Excessive daytime sleepiness
- Cataplexy: sudden loss of muscle tone from the away state, often in response to an emotional stimulus
- Dreamlike hallucinations when falling asleep or awakening
- Sleep paralysis: awaking, but remaining unable to move for several minutes
Describe the symptoms of a REM sleep behavioral disorder
- Complex motor activity during dreaming (re-enacting dreams, ranges in severity)
- Lack of descending inhibition to LMN (muscle tone does not decrease like it is supposed to)
- Can be a precursor of parkinsonism
What does a coma look like?
- Unarousable
- No purposeful response by cortex
- Brainstem reflexes may be present
- Eyes closed
- Minimum duration 1 hour
- EEG shows abnormal activation patterns
- Cerebral metabolism is less than 50%
What does a vegetative state look like?
- No purposeful response by cortex
- Can open eyes and arouse in response to stimulus
- Sleep-wake cycles intact
- Primitive orienting responses mediated by the brainstem and diencephalon
- Cerebral metabolism is less that 50%
What does a minimally conscious state look like?
- Some responsiveness (may be minimal or variable)
- No reliable communication (verbal/non-verbal)
- No functional use of objects
What does brain death look like?
- Extreme and irreversible form of coma
- No evidence of forebrain or brainstem function
- No brainstem reflexes
- Spinal reflexes may be present
- EEG is flat
- Cerebral metabolism 0%
The caudal reticular formation is involved in what functions?
- Control of respiration
- Control of HR and BP
- Abnormal posturing
- Cranial nerve reflexes
- Behaviors (coughing, hiccupping, sneezing, yawning, shivering, gagging, vomiting, swallowing, laughing, crying)
- Sphincter control
