Reticular Formation and monoamines Flashcards
Understand the Reticular Formation Definition and diffuse Zones Descending reticulospinal pathways overview of reticular formation functions reticular nuclei and there neurotransmitters ++monoaminergic pathways affecting consciousness and attention
What is a diffusely organized area forming the central core of the brainstem
The Reticular Formation
What is a diffusely organized area forming the central core of the brainstem
The Reticular Formation
1 Reticular Formation Neuron may synapse with
25000 other neurons
The reticular formation connects to a different areas by a great deal of convergence and divergence
in the Brainstem, Cerebellum, Cerebrum, and Spinal Cord
The reticular formation areas overlap considerable in Function
True
The Reticular Formation consist of which zone
Medial and Lateral
and midline zone
The lateral zone receives most
afferent input and projects to the medial –the output (efferent) area.
Which two descending pathways send major projections into the spinal cord
Medial (pontine) reticulospinal tract
Lateral (medullary) reticulospinal tract
What is the function of the lateral zone
integrates sensory and cortical input for generalized arousal
What is the function of the medial zone
regulates vital functions somatic motor activity and attention
What is the function of the midline zone
adjust transmission of pain information, somatic motor activity and conscious levels
Pontine (Medial) Reticular formation
Uncrossed medial reticulospinal tract
+In brainstem this tract travels just ventral to the MLF
+Descends all SC levels
Mainly an excitatory + function on extensor alpha motorneurons
+Especially to trunk and proximal extremity muscles
Brainstem UMN overreactivity leads to spasticity and hyperreflexia
+indicates excessive reticulospinal or vestibulospinal trace signals to LMN’s
Medullary (Lateral Reticular Formation)
Primary uncrossed lateral reticulospinal tract
Descends to all SC levels
++Tract conveys autonomic+ information from higher levels to preganglionic ANS neurons++
++Influencing respiration, circulation, sweating/shivering, pupil dilation, visceral wall smooth muscle++
Role(?) with alpha/beta/gamma neurons
What is the reticular connection to sensory control?
Integrates cerebral cortex and sensory
+motivation, decision-making, moods
What is the reticular formation function in motor control
Regulates somatic motor activity
what is the reticular connection to visceral control
regulates ANS function
Reticular Formation connection with Control of Conscious
regulates levels of consciousness
+sleeping-waking cycles
What is the reticular connection for Pain Control
Modulates nocioceptive information
RF Sensory Control:
Reticular neurons exert control over activity in the
**Spinal polysynaptic reflex arcs (supraspinal control)
RF Sensory Control:
**Tonic inhibition (-) of flexor reflexes originates in the Reticular formation
RF Sensory Control
**Important in the regulation of pain perception by
inhibiting some sensory interneurons and tracts in the spinal cord
RF: Motor Control
Some regions closely associated with the cerebellum and its motor functions
It receives input from the red nucleus** in the midbrain
RF: Motor control
2 descending reticulospinal tracts in near the MLF**
A major alternate route to the pyramidal tract by which spinal motor neurons are controlled
–Also carry descending motor commands generated in the RF itself
RF: Visceral Control • Visceral information reaches the RF • programs appropriate responses to environmental changes • projects to the autonomic nuclei of the brainstem and spinal cord • **Control centers for inspiration, expiration, and normal breathing rhythm • ** Control centers controlling heart rate and blood pressure
Control of Consciousness (ARAS)
• **Ascending Reticular Activating System
• Ascending projections from RF
terminate in the thalamus, subthalamus,
hypothalamus, and cerebral basal nuclei
(caudate, putamen, globus pallidus)
• Activity in the pathway to the thalamus
is essential in maintenance of a normal
state of consciousness
• RF input to the normal cerebrum is needed
for conscious functioning
Ascending
Reticular Activation System [ARAS]
• **ARAS - Not to be confused with the descending
tracts of the reticular formation
• These reticulocortical pathways project through
the thalamus, lateral hypothalamus and **basal
forebrain
• On their way from the brainstem to the cerebral cortex
• Tied into levels of consciousness (a prerequisite
for perception)
• Awareness of self and surroundings
• Regulation of sleep and wakefulness cycles–
alertness and attention
Reticular *Nuclei and their *Neurotransmitters
• Reticular nuclei regulate neural activity
throughout the CNS
• Neurons in each nucleus produce a different
neurotransmitter
• **Neuromodulators are chemicals (slow acting)
that alter other neurotransmitter release (fast
acting) or the response of receptors to
neurotransmitters
• These neuromodulators influence activity in
other parts of the brainstem, cerebrum and
cerebellum
Ascending projections from RF terminate in the
thalamus, subthalamus, hypothalamus (part of diencephalon) and cerebral basal nuclei ( caudate putamen, globus pallidus)
Activity in the pathway to the thalamus is essential in
maintenance of a normal state of consciousness
RF input to the normal cerebrum is needed for
conscious functioning
What is the ARAS
the ascending reticular activation system is not the be confused with the descending tracts of the reticular formation
The ARAS reticulospinal pathways project
through the thalamus, lateral hypothalamus and basal forebrain
1 Reticular Formation Neuron may synapse with
25000 other neurons
The reticular formation connects to a different areas by a great deal of convergence and divergence
in the Brainstem, Cerebellum, Spinal Cord
The reticular formation areas overlap considerable in Function
True
The Reticular Formation consist of which zone
Medial and Lateral
and midline zone
The lateral zone receives most
afferent input and projects to the medial –the output (efferent) area.
Which two descending pathways send major projections into the spinal cord
Medial (pontine) reticulospinal tract
Lateral (medullary) reticulospinal tract
What is the function of the lateral zone
integrates sensory and cortical input for generalized arousal
What is the function of the medial zone
regulates vital functions somatic motor activity and attention
What is the function of the midline zone
adjust transmission of pain information, somatic motor activity and conscious levels
Pontine (Medial) Reticular formation
Uncrossed medial reticulospinal tract
+In brainstem this tract travels just ventral to the MLF
+Descends all SC levels
Mainly an excitatory + function on extensor alpha motorneurons
+Especially to trunk and proximal extremity muscles
Brainstem UMN overreactivity leads to spasticity and hyperreflexia
+indicates excessive reticulospinal or vestibulospinal trace signals to LMN’s
Medullary (Lateral Reticular Formation)
Primary uncrossed lateral reticulospinal tract
Descends all SC levels
Tract conveys autonomic information from higher levels to preganglionic ANS neurons
+Influencing respiration, circulation, sweating/shivering, pupil dilation, visceral wall smooth muscle
Role(?) with alpha/beta/gamma neurons
What is the reticular connection to sensory control?
Integrates cerebral cortex and sensory
+motivation, decision-making, moods
What is the reticular formation to motor control
Regulates somatic motor activity
what is the reticular connection to visceral control
regulates ANS function
Control of Conscious
regulates levels of consciousness
+sleeping-waking cycles
What is the reticular connection for Pain Control
Modulates nocioceptive information
Sensory Control:
Reticular neurons exert control over activity in the
Spinal polysynaptic reflex arcs (supraspinal control)
Sensory Control
Tonic inhibition (-) of flexor reflexes originates in the Reticular formation
Sensory Control
Importatn in the regulation of pain perception by
inhibiting some sensory interneurons and tracts in the spinal cord
Motor Control
Some regions closely associated with the cerebellum and its motor functions
It receives input from the red nucleus in the midbrain
Motor control
2 descending reticulospinal tracts in near the MLF
A major alternate route to the pyramidal tract by which spinal motor neurons are controlled
–Also carry descending motor commands generated in the RF itself
Visceral Control • Visceral information reaches the RF • programs appropriate responses to environmental changes • projects to the autonomic nuclei of the brainstem and spinal cord • Control centers for inspiration, expiration, and normal breathing rhythm • Control centers controlling heart rate and blood pressure
Control of Consciousness (ARAS)
• Ascending Reticular Activating System
• Ascending projections from RF
terminate in the thalamus, subthalamus,
hypothalamus, and cerebral basal nuclei
(caudate, putamen, globus pallidus)
• Activity in the pathway to the thalamus
is essential in maintenance of a normal
state of consciousness
• RF input to the normal cerebrum is needed
for conscious functioning
Ascending
Reticular Activation System [ARAS]
• ARAS - Not to be confused with the descending
tracts of the reticular formation
• These reticulocortical pathways project through
the thalamus, lateral hypothalamus and basal
forebrain
• On their way from the brainstem to the cerebral cortex
• Tied into levels of consciousness (a prerequisite
for perception)
• Awareness of self and surroundings
• Regulation of sleep and wakefulness cycles
alertness and attention
Reticular Nuclei and their Neurotransmitters
• Reticular nuclei regulate neural activity
throughout the CNS
• Neurons in each nucleus produce a different
neurotransmitter
• Neuromodulators are chemicals (slow acting)
that alter other neurotransmitter release (fast
acting) or the response of receptors to
neurotransmitters
• These neuromodulators influence activity in
other parts of the brainstem, cerebrum and
cerebellum
Ascending projections from RF terminate in the
thalamus, subthalamus, hypothalamus (part of diencephalon) and cerebral basal nuclei ( caudate putamen, globus pallidus)
Activity in the pathway to the thalamus is essential in
maintenance of a normal state of consciousness
RF input to the normal cerebrum is needed for
conscious functioning
What is the ARAS
the ascending reticular activation system is not the be confused with the descending tracts of the reticular formation
The ARAS reticulospinal pathways project
through the thalamus, lateral hypothalamus and basal forebrain
Neurotransmitters:Chemical Neuroanatomy
Neuropharmacology–research deals with neurotransmitters, their receptor types, and how they interact (inhibitory and excitatory)
Neurons communicate with each other primarily by the
release of neurotransmitters at chemical synapses.
Monoamines (aromatic amino acids) are
one class of neurotransmitters well studied.
Monoaminergic Pathways
are known to contribute to behavior and mood swings
Changes in mood can be a symptom or
different medical and neurological diseases that affect these pathways.
ex. strokes, multiple sclerosis, Huntington disease and Parkinson disease
Monoaminergic Pathways have 4 major systems
Serotonin
Dopamine
Acetylcholine
Noadrenalin (norepinephrine)
\+Adrenalin(Epinephrine)All of the 4 major systems of monoaqminergic pathways have cell populations
close to or within the reticular formation
The axonal Projections of these cells
reach all major regions of the CNS
Major Reticular Nuclei
- Ventral Tegmental Area (dopamine for Cerebrum)
- Pedunculopontine Nucleus (acetylcholine for cerebrum)
- Raphe Nuclei (serotonin)
- Locus coeruleus and medial reticular nuclei (norepinephrine and epinephrine)
Dopamine affects
Motivation and decision making
Dopamine is located
in substantia nigra and ventral tegmental area (VTA*)
- –only the VTA is part of the reticular formation
- –Activation of ventral striatum —-feelings of pleasure and reward
Dopamine is associated with a dysfunction (excessive activation) implicated in pathophysiology of schizophrenia…
- A disorder of perception
- Neuroleptics (tranqulizers, anti psychotics, morphine) have high affinity for DA-receptors
- Amphetamine/cocaine addiction–activate VTA (inhibits inhibitory inputs to VTA)
4.Affects the positive symptoms of schizophrenia => hallucinations, delusions,
disorder of thought processing; [not the
disabling negatives => apathy, social withdrawal, eccentricity]
Acetylcholine
• PPN (caudal midbrain)
• Influences movement through connections
• Globus pallidus and subthalamic nucleus
• Limbic system
• Reticular areas giving rise to reticulospinal
tracts
• Parkinson’s disease
• Loss of PPN explains dopamine-resistant
signs of difficulty initiating gait, postural
instability, sleep problems
• Cat studies
• Stimulation of PPN induces walking without
cerebral connections
ALZHEIMER’S DISEASE
Sharp decrease in concentration of
cholinergic (acetylcholine) markers in
cerebral cortex and hippocampus
• Also affected, but in more variable fashion is
norepinephrine, serotonin, and substance P
• Substance P is a neuropeptide (neurokinin)
associated with acetylcholine and serotonin; has
excitatory effect on substantia gelatinosa, globus
pallidus and substantia nigra
SEROTONIN: 5-Hydroxytryptamine
Raphe Nuclei: in brainstem Midline
—Influence cerebral arousal levels
Terminals are dense in limbic areas
—Midbrain raphe nuclei project throughout the cerebrum
—pontine raphe nuclei modulate neural activity in Brainstem and Cerebellum
1. Physiologic roles proposed include: for arousal vs. sleep, pain transmission, mood disorders, aggression
—-Prozac(fluoxetine) prolongs availability of serotonin
2. Inhibit pain fibers in dorsal gray horn
3. Facilitates LMNs in ventral gray horn
SEROTONIN
Depletion of brain serotonin affects mood and results in:
- Increased irritability and aggression
- Passionless, violent behavior directed at others or physically destructive (Suicide)
- Norepinephrine and /or serotonin are critically involved in the pathophysiology of severe depression=leads to sleep disorders, weight loss, kinetic abnormalities, and anhedonia (inability to experience pleasure)
Norepinephrine
Locus coeruleus (principal nucleus) in lower midbrain and upper pons
—source of most norepinephrine
—innervates all regions of the CNS: cerebellum, brainstem, cerebrum, and spinal cord
Directs attention and focus
—inactive during sleep
—coeruleospinal tract to dorsal gray horn–inhibit spinothalamic pain information
Norepinephrine and Epinephrine
Medial Reticular Zone projects to hypothalamus, brainstem nuclei, and lateral horn of Spinal Cord
Medial reticular zone produces both norepinephrine and epinephrine
—respiratory
—Visceral
—Cardiopulmonary
Figure 17-23
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