The Autonomic Nervous System (Ch 13). Two Major Divisions of the Nervous System Central Nervous...

The Autonomic Nervous System (Ch 13)

Two Major Divisions of the Nervous System

Central Nervous System (CNS) Brain and spinal cord

Peripheral Nervous System all nervous tissue outside the CNS, including

sensory and motor neurons

Basic Functions of the Nervous System

Recognizing changes in Internal environment External environment

Processing and integrating environmental changes

Reacting to environmental changes by producing and action or response

Figure 13.1 Functional divisions of the peripheral nervous system.

Divisions of the Peripheral Nervous System

Somatic nervous system Voluntary control over skeletal muscles

Autonomic nervous system Involuntary control over smooth and cardiac muscle

and glands

Autonomic Nervous System:Sympathetic Nervous System

Activated under stressFight-or-flight responseReady the body for an immediate response

to a potential threat

Autonomic Nervous System: Parasympathetic Nervous System

Activated under nonstressful conditionsRest-and-digest responseDigestive processes promoted, heart rate

and blood pressure decline

Autonomic Nervous System: Sympathetic and Parasympathetic Divisions

Branches produce mostly opposite effectsHomeostasis – proper balance of the two

branches achieved by changing one or both branches

Branches do not always produce opposite effects

Figure 13.2 Effects of the sympathetic and parasympathetic nervous systems. Source: Biology Guide to the Natural World, 2nd ed (p. 558) by David Krogh, 2002 Upper Saddle River, NJ, Prentice Hall. Reprinted by permission.

Synaptic Transmission

Synapse – juncture of neuronsConnection of two neurons outside CNS –

ganglionic synapse Preganglionic neuron Postganglionic neuron

Many drugs affect autonomic function by altering neurotransmitter activity at the second synapse

Five Mechanisms by Which Drugs Can Affect Synaptic Transmission

1. Affect the synthesis of the neurotransmitter in the presynaptic nerve

2. Prevent storage of the neurotransmitter in vesicles within the presynaptic nerve

3. Influence release of the neurotransmitter from the presynaptic nerve

4. Prevent the normal destruction or reuptake of the neurotransmitter

5. Bind to the receptor site on the postsynaptic target tissue

Drugs Not Given to Correct Autonomic Nervous System

System is relatively free of diseaseDrugs used to stimulate or inhibit target

organs of the autonomic nervous system

Figure 13.3 Basic structure of the autonomic pathway.

Figure 13.4 Receptors in the autonomic nervous system: (a) sympathetic division; (b) parasympathetic division

Primary Neurotransmitters of Autonomic Nervous System

Norepinephrine (NE)Acetylcholine (Ach)

Norepinephrine

Released by most postganglionic nervesClass of agents called natural

catecholamines, all involved in neurotransmission

Adrenergic receptors - receptors at the ends of postganglionic sympathetic neurons

Two Types of Adrenergic Receptors

Alpha-receptors and Beta-receptorsHugely important to pharmacologyDrugs are selective and activate only one

type of adrenergic receptor, whereas others affect all receptor subtypes

Alpha1-adrenergic Receptors

In all sympathetic target organs except heart

Response Constriction of blood vessels Dilation of pupils

Alpha2-adrenergic Receptors

At presynaptic adrenergic neuron terminalsActivation inhibits release of

norepinephrine

Beta1-adrenergic Receptors

In heart and kidneysResponse

Activation increases heart rate and force of contraction of heart.

Increases release of renin

Beta2-adrenergic Receptors

In all sympathetic target organs except the heart

Inhibit smooth muscle

Prototype Drug: Phenylephrine (Neo-Synephrine)

Norepinephrine (NE) is synthesized

In the nerve terminalRequires the amino acids phenylalanine and

tyrosineConversion of dopamine to norepinephrineNE in nerve terminal may be returned to

vesicles for future use, or destroyed enzymatically by monoamine oxidase

Adrenal Medulla

Anatomic and physiologic arrangement much different from rest of sympathetic branch

Other types of adrenergic receptors

Dopamine serves a larger role as a neurotransmitter

Acetylcholine

Released by cholinergic nervesTwo types cholinergic receptors

Muscarinic receptors Nicotinic receptors

Nicotinic Receptors

In sympathetic and parasympathetic divisions at the ganglionic synapse

Response Stimulate smooth muscle Stimulate gland secretion

Muscarinic Receptors

In parasympathetic target organs except the heart Response

Stimulate smooth muscle Stimulate gland secretion

In heart: decreased heart rate and force of contraction

Physiology of Acetylcholine

Affords several mechanisms by which drugs may act

Synthesized in presynaptic nerve terminal from choline and acetyl coenzyme A

Ach in the synaptic cleft is rapidly destroyed by the enzyme acetylcholinesterase (AchE)

Classification and Naming of Autonomic Drugs

Based on four possible actions of sympathetic and parasympathetic nervous systems

Stimulate sympathetic nervous system Adrenergic agents or sympathomimetics

Inhibit sympathetic nervous system Adrenergic-blocking agents, adrenergic antagonists,

or sympatholytics

Classification and Naming of Autonomic Drugs (cont'd)

Stimulate parasympathetic nervous system Cholinergic agents or parasympathomimetics

Inhibit parasympathetic nervous system Cholinergic-blocking agents, anticholinergics,

parasympatholytics, or muscarinic blockers

One of Four Drug Classes is Most Important to Learn

If the fight-or-flight actions of the sympathomimetics are learned, the other three groups can be deduced

Mastering the actions and terminology of autonomic drugs early will pay dividends later

Role of Nurse

Monitor patient’s conditionProvide education on drug therapyNote adverse effects of drug therapyIdentify possible interactionsIdentify contraindications of drug therapy

Sympathomimetic

Monitor vital signs, urinary and cardiac output as appropriate

Monitor breathing patternsObserve patient’s responsiveness to lightMonitor for rhinorrhea and epistaxis

Nursing Process Focus: Patients Receiving Adrenergic (Sympathomimetic Therapy)

Anticholinergics

Monitor for signs of anticholinergic crisisReport changes in heart rate, blood

pressure, or development of dysrhythmiasProvide comfort measures for dry mouth

Anticholinergic (cont'd)

Minimize exposure to heat or cold or strenuous exercise

Monitor intake and outputMonitor patient for abdominal distension,

and auscultate for bowel sounds

Nursing Process Focus: Patients Receiving Anticholinergic Therapy

Adrenergic Blockers

Monitor urinary hesitancy, incomplete bladder emptying, interrupted urinary stream

Monitor vital signs, level of consciousness, and mood

Monitor for dizziness, drowsiness, or light-headedness

Observe for side effectsMonitor cardiac output

Nursing Process Focus: Patients Receiving Adrenergic-Blocker Therapy

Parasympathomimetics

Monitor for adverse effectsMonitor liver enzymesCalculate and monitor dosesAssess and monitor for appropriate self-care

administration

Direct Acting

Monitor intake and output ratioMonitor for blurred visionMonitor for orthostatic hypotension

Cholinesterase Inhibitors

Monitor muscle strength and neuromuscular status

Monitor ptosis, diplopia, and chewingSchedule medication around mealtimesSchedule activities to avoid fatigueMonitor for muscle weakness

Nursing Process Focus: Patients Receiving Parasymptathomimetic Therapy

Adrenergic Agents (Sympathomimetics)

Prototype drug: phenylephrine (Neo-Synephrine) Mechanism of action: to stimulate the sympathetic

nervous system directly/indirectly produce many of the same responses as the

anticholinergics

Adrenergic Agents (Sympathomimetics) (cont'd)

Primary use: depends on receptors activated Alpha1-receptors: nasal congestion, hypotension,

dilation of pupils for eye examination Alpha2-receptors: hypertension Beta1-receptors: cardiac arrest, heart failure, shock Beta2-receptors: asthma and premature-labor

contractions

Adrenergic Agents (Sympathomimetics) (cont'd)

Adverse effects: tachycardia, hypertension, dysrhythmias, CNS excitation and seizures, dry mouth, nausea and vomiting, anorexia

Adrenergic-Blocking Agents

Prototype drug: prazosin (Minipress)Mechanism of action: to inhibit the

sympathetic nervous systemPrimary use: hypertension, dysrhythmias,

angina, heart failure, benign prostatic hypertrophy, narrow-angle glaucoma

Adverse effects: dizziness, drowsiness, headache, loss of energy and strength, palpitations, dry mouth

Prototype Drug: Prazosin (Minipress)

Adrenergic-Blocking Agents

Primary use of beta blockers is in the treatment of hypertension

Beta-adrenergic antagonists have several other important therapeutic applications angina pectoris Migranes Heart failure

Cholinergic Agents (Parasympathomimetic)

Prototype drug: bethanechol (Urecholine)Mechanism of action: to activate the

parasympathetic nervous system directly/indirectly, induce rest/digest response

Uses: glaucoma, urinary retention, myasthenia gravis, Alzheimer’s disease

Adverse effects: profuse salivation, sweating increased muscle tone, urinary frequency, bradycardia

Prototype Drug: Bethanechol (Duvoid,Urecholine)

Cholinergic Agents (Parasympathomimetic)

Divided into two classes direct acting

bind to cholinergic receptors to produce the rest-and-digest response

indirect acting inhibit the action of AchE

High potential for serious adverse effects

Cholinergic-Blocking Agents

Prototype drug: atropine (Atropair, Atropisol)Mechanism of action: to inhibit the

parasympathetic nervous systemPrimary use: peptic ulcers, irritable bowel

syndrome, mydriasis and cycloplegia during eye examination, bradycardia, preanesthetic, asthma

Adverse effects: tachycardia, CNS stimulation, urinary retention, dry mouth, dry eyes, decreased sweating, photophobia

Prototype Drug: Atropine (Atro-Pen, Atropair,Atropisol)

Drugs Affecting the Autonomic Nervous System

Assessment Potential nursing diagnoses Reason for drug Monitoring vital signs Doing complete health history

Drugs Affecting the Autonomic Nervous System (cont'd)

Cautions and contraindications for drug Allergies Drug history Possible drug interactions Evaluating lab findings Assess for therapeutics effect Watch for adverse effects


Nursing Diagnosis Knowledge deficient, related to drug therapy Risk for injury, related to side effect of drug therapy Disturbed sleep pattern


Planning Patient will exhibit therapeutic outcome based on

specific drug Patient will demonstrate an understanding of drug’s

activity Patient will accurately describe drug side effects

and precautions Patient will demonstrate proper administration

technique


Implementation Administration of drug Observing for adverse effects Patient education/discharge planning Providing additional information as needed to

encourage compliance Doing home-health visits


Evaluation Evaluating effectiveness of drug therapy Confirming that patient goals and expected

outcomes have been met

NCLEX-RN ReviewQuestion 1

1. Following administration of an adrenergic (sympathomimetic) drug, the nurse would

assess for which adverse drug effects?

1. Insomnia, nervousness, and hypertension 2. Nausea, vomiting, and hypotension 3. Nervousness, drowsiness, and dyspnea 4. Bronchial dilation, hypotension, and

bradycardia

NCLEX-RN ReviewQuestion 1 – Rationale

Rationale: Adrenergic agonists stimulate the sympathetic nervous system and produce symptoms of the fight-or-flight response. Nausea, vomiting, nervousness, bronchial dilation, and hypertension are potential adverse reactions related to the use of adrenergic agonists. Hypotension is a potential adverse reaction related to the use of adrenergic antagonists.


2. Adrenergic-blocking (antagonist) drugs may include all of the following adverse reactions except:

1. Bronchodilation 2. Tachycardia 3. Edema 4. Heart failure


Rationale: Potential adverse reactions associated with the use of adrenergic antagonists include tachycardia, edema, and heart failure. Bronchodilation is associated with the use of adrenergic agonists.

Cognitive Level: AnalysisNursing Process: Assessment Patient Need: Physiological Integrity


3. Elderly patients taking bethanechol (Urecholine) need to be assessed more frequently because of which of the following side effects?

1. Diaphoresis 2. Hypertension 3. Dizziness 4. Urinary retention


Rationale: The nurse should monitor elderly patients for episodes of dizziness caused by CNS stimulation from the parasympathomimetic. Diaphoresis and dizziness are potential side effects related to the use of bethanechol. Bethanechol is used to treat nonobstructive urinary retention.

Cognitive Level: ApplicationNursing Process: ImplementationPatient Need: Physiological Integrity


4. The patient taking benztropine (Cogentin) should be assessed for:

1. Heartburn 2. Constipation 3. Hypothermia 4. Increased gastric motility


Rationale: Anticholinergic medications slow intestinal motility; therefore, constipation is a potential side effect. Heartburn and hypothermia are not associated with the use of benztropine.

Cognitive Level: ApplicationNursing Process: AssessmentPatient Need: Physiological Integrity


5. The patient taking tacrine (Cognex) should be observant for which of the following adverse effects that may signal a possible overdose has occurred?

1. Excessive sweating, salivation, and drooling2. Extreme constipation 3. Hypertension and tachycardia 4. Excessively dry eyes and reddened sclera


Rationale: Overdosage of parasympathomimetics (cholinesterase inhibitors) may produce excessive sweating, drooling, dyspnea, or excessive fatigue. These symptoms should be promptly reported.

Cognitive Level: ComprehensionNursing Process: AssessmentPatient Need: Physiological Integrity

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