Reticular Formation

Question 1

What is the reticular formation?

Answer 1

• 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

Question 2

Describe the structure and function of the rostral reticular formation

Answer 2

• Consists of nuclei in the midbrain, upper pons, diencephalic nuclei
• Maintains alert conscious state in the forebrain

Question 3

Describe the structure and function of the caudal reticular formation

Answer 3

• Consists of nuclei in the pons, medulla, cranial nerve nuclei, and spinal cord
• Carries out important motor, reflex, and autonomic functions

Question 4

What are the three levels of consciousness?

Answer 4

Alertness
Attention
Awareness

Question 5

Describe pathway of the pontomesencephalic reticular formation

Answer 5

• 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

Question 6

Describe the pathway of the basal forebrain that communicates via acetylcholine

Answer 6

• Basal forebrain sends acetylcholine to the cerebral cortex and hippocampus
• Effects attention, memory, and learning

Question 7

Describe the pathway of the pontomesenphalic region that communicates via acetylcholine

Answer 7

• 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

Question 8

Describe the mesostriatal pathway

Answer 8

Dopamine from SNc and ventral tegmental area is sent to the caudate and the putamen for basal ganglia functions

Question 9

Describe the mesolimbic pathway

Answer 9

Dopamine from the SNc and ventral tegmental area is sent to limbic structures to influence reward and addiction

Question 10

Describe the mesocortical pathway

Answer 10

Dopamine from the SNc and ventral tegmental area is sent to the prefrontal cortex to influence working memory and attentional aspects of movement intiation

Question 11

Describe the norepinephrine pathway in the reticular formation

Answer 11

• 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

Question 12

Describe the serotonin pathway involving the rostral raphe nucleus

Answer 12

• The rostral raphe nucleus sends serotonin to the cortex, basal ganglia, and thalamus
• Plays a role in some psychiatric symptoms

Question 13

Describe the serotonin pathway involving the caudal raphe nucleus

Answer 13

• 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

Question 14

Describe the histamine pathway in the reticular formation

Answer 14

• Neurons in the posterior hypothalamus send histamine to the thalamus (excitatory), and the cortex (excitatory/inhibitory)
• Helps maintain alert state

Question 15

Describe the orexin pathway in the reticular formation

Answer 15

• Neurons located in the posterior lateral hypothalamus send orexin to the cortex and all brainstems arousal systems
• Promotes staying awake

Question 16

Describe the GABA pathway in the reticular formation

Answer 16

• 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

Question 17

Describe the stages of sleep

Answer 17

• Non-REM: consists of three stages (N1, N2, N3) that get progressively deeper
• REM: low muscle tone, dreaming, EEG is similar to wakeful state

Question 18

Which neurotransmitters are active during wakefulness?

Answer 18

Acetylcholine, serotonin, norepinephrine, dopamine, and orexin are all rapidly firing

Question 19

Which neurotransmitters are active during non-REM sleep?

Answer 19

GABA is rapidly firing and serotonin, norepinephrine, and dopamine are slowly firing

Question 20

Which neurotransmitters are active during REM sleep?

Answer 20

Acetylcholine and GABA are rapidly firing

Question 21

What is occurring during non-REM sleep?

Answer 21

• 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

Question 22

What is occurring during REM sleep?

Answer 22

• 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

Question 23

How does the anterior hypothalamus contribute to sleep?

Answer 23

• Ventral lateral pre-optic area inhibits arousal systems in the posterior hypothalamus and brainstem to promote REM sleep
• Lesion = insomnia, cannot inhibit arousal systems

Question 24

How does the posterior hypothalamus contribute to sleep?

Answer 24

• Glutamate, histamine, and orexin help maintain alert state
• Lesion = hypersomnia, no alert state

Question 25

What is narcolepsy?

Answer 25

Abnormal tendency to easily enter REM sleep directly from waking

Question 26

What are the four classic presentations of narcolepsy?

Answer 26

- 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

Question 27

Describe the symptoms of a REM sleep behavioral disorder

Answer 27

- 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

Question 28

What does a coma look like?

Answer 28

- 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%

Question 29

What does a vegetative state look like?

Answer 29

- 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%

Question 30

What does a minimally conscious state look like?

Answer 30

- Some responsiveness (may be minimal or variable) - No reliable communication (verbal/non-verbal) - No functional use of objects

Question 31

What does brain death look like?

Answer 31

- 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%

Question 32

The caudal reticular formation is involved in what functions?

Answer 32

- 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