Download Unit 13 Autonomic Nervous System

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Unit 12
Autonomic Nervous System
Divisions
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• The nervous system is divided into central and peripheral components
• Central Nervous System
– Brain
– Spinal Cord
• Peripheral Nervous System
– Somatic
– Autonomic
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Structural Division PNS
• Sensory
– Recognize changes to the environment
• Motor
– Respond to changes by moving muscles or secreting chemicals
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Structural Division
PNS
• Somatic
– Voluntary control over skeletal muscle
• Autonomic
– Involuntary control
– sympathetic and parasympathetic branches
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Subsystems
• Sympathetic
– Fight or flight response
– Times of stress
• Parasympathetic
– Rest and digest
– Non-stressful situations
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Figure 8.2 Effects of the sympathetic and parasympathetic nervous systems Source: Pearson Education/PH College
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Autonomic Nervous System
• Involuntary Control
– Smooth Muscle
– Cardiac Muscle
– Glands
• Branches
– Sympathetic
– Parasympathetic
– Almost all organs and glands receive nerves from both branches
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The Neuron
• Functional cell of the nervous system
• Transmits information
– Throughout nervous system
– To muscle and glands
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Synapse
• Synapses are common sites of drug action
• Area at the end of the neuron
• Synaptic cleft
– Space between neurons
– Nerve impulses must cross to reach next neuron
• Presynaptic Neuron
– Before the synapse
– Generates original impulse
• Postsynaptic Neuron
– On other side of synapse
– Waiting to Receive impulse
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Figure 8.3 A nerve impulse travels along the presynaptic neuron, bridges the synaptic cleft, and reaches the receptors in the postsynaptic neuron. There, the impulse is regenerated.
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Neurotransmitters
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Chemicals released by presynaptic neurons into synaptic cleft
Attach to receptors on postsynaptic neurons
Regenerate nerve impulse
Acetylcholine and norepinephrine are the two primary neurotransmitters in the
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Important Neurotransmitters
• Norepinephrine (adrenergic)
– Released by sympathetic nerves at synapse with organs
• Acetylcholine (cholenergic)
– Released by all presynaptic neurons at synapse with ganglia
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Cholinergic Receptors
• Nicotinic
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– Found in ganglia and skeletal muscle
• Muscarinic
– End of postsynaptic neurons in parasympathetic nervous system
Adrenergic Receptors
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• Norepinephrine
• alpha 1
– All sympathetic target organs
– Except the heart
• alpha 2
– Presynaptic adrenergic neuron terminals
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• beta1
– Heart
– Kidney
• beta 2
– All sympathetic target organs
– Except the heart
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Figure 8.4 Norepinephrine (NE) receptors are adrenergic receptors (α and β) in the sympathetic pathway. Acetylcholine (Ach) receptors in the ganglia and skeletal muscles (not shown here) are called
nicotinic. Ach receptors at the ends of postganglionic neurons in the parasympathetic pathway are called muscarinic.
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• Autonomic drugs are classified according to the receptors they stimulate or block
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Four Actions
• Stimulation of sympathetic nervous system
– Sympathomimetics or adrenergic agents
• Stimulation of parasympathetic nervous system
– Parasympathomimetics or cholinergic agents
• Inhibition of sympathetic nervous system
– Adrenergic blockers or sympatholytics
• Inhibition of parasympathetic nervous system
– Anticholinergics or cholinergic blockers
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• Parasympathomimetics have few therapeutic uses because of their numerous
adverse effects
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Direct-Acting Parasympathomimetics
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Used only in the clinical setting
Serious adverse effects
Reduce intraocular pressure in glaucoma
Stimulate smooth muscle in bowel and urinary tract after anesthesia
Indirect-Acting Parasympathomimetics
• Acetylcholinesterase inhibitors
• Facilitate effects of acetylcholine
• Same effects as direct-acting agents
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Uses
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Affect acetylcholine receptors in skeletal muscles
Use with myasthenia gravis
Stimulate skeletal muscle contractions
Temporarily restore muscle strength
Examples
– pyridostigmine (Mestinon)
– Neostigmine (Prostigmin)
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Adverse Effects
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Increased salivation
Increased sweating
Muscle twitching
Involuntary defecation and urination
Confusion
Convulsions
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Anticholinergic Drug Actions
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Therapeutic Uses for Anticholinergic Agents
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Anticholinergics are used to dry secretions and to treat asthma
Opposite of the parasympathetic nervous division
Mimic fight-or-flight response
Block muscarinic receptors
Dilation of pupils
Increase heart rate
Drying of secretions
Dilation of bronchi
Adverse Effects Limit Their Usefulness
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• Tachycardia
• Urinary retention in men with prostate disorders
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Sympathomimetics
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Primarily used for their effects on the heart, bronchial tree, and nasal passages
Produce same effects as anticholinergics
Mimic sympathetic nervous system
Stimulate alpha and beta receptors
Actions more specific
Wider therapeutic uses
Sympathomimetics
• Affect Alpha and Beta Receptors
– Heart
– Bronchial tree
– Nasal passages
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Selective Sympathomimetics
• Stimulate Certain Adrenergic-Subreceptors
– Alpha1 receptors
• Located in nasal passages
• Dry nasal secretions
– Beta1 receptors
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Selective Sympathomimetics
• Located in the heart
• Increase heart rate
• Increase force of contractions
– Beta2 receptors
• Located in the bronchi
• Bronchodilation
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Nonselective Sympathomimetics Stimulate
• All adrenergic receptors
– Epinephrine
– Used in cardiac arrest and asthma
• Alpha1 and beta2 receptors
– Pseudoephedrine
– Oral nasal decongestant
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Nonselective Sympathomimetics Stimulate
• Beta1 and beta2 receptors
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– Isoproterenol
– Increases rate, force, and conduction speed of heart
– More autonomic-related side effects
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Adrenergic Blockers
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Primarily used to treat hypertension
Most widely prescribed class of autonomic drugs
Inhibit sympathetic nervous system
Produce same response as parasympathomimetics
Most widely used class of autonomic drugs
Used to treat hypertension
Adrenergic Blockers
• Alpha1 Blockers
– Relax vascular smooth muscle
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Causes vasodilation
Decreases blood pressure
Treat hypertension
Doxazosin (Cardura)
Adrenergic Blockers
• Beta1 Blockers
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Beta1 receptors found only in heart
Slow heart rate and lower blood pressure
Cardioselective
Atenolol (Tenormin)
Adrenergic Blockers
• Some Beta Blockers Block Both Beta1 and
– Beta2 Receptors
– Nonselective
– Used to treat
• Hypertension
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Adrenergic Blockers
• Angina
• Cardiac arrhythmias
– More side effects
– Propranolol (Inderal)
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Review
• The nurse recognizes that which of the following drugs is contraindicated in
patients with glaucoma?
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Review
Alpha1-adrenergic blockers cause what to occur in the body?
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Review
• How would a person who is engaging in stressful or energetic activity benefit
from the sympathetic effects of bronchodilation, slowed GI motility, and pupil
dilation?
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Review
• Why do the sympathomimetics produce many of the same symptoms as the
anticholinergics?
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Review
• Both parasympathomimetics and adrenergic blockers produce similar actions.
Why are the adrenergic blockers used to treat hypertension, but the
parasympathomimetics not used for this purpose?
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