Introduction to the Autonomic Nervous System

Autonomic Nervous System (ANS)

Referred to as the involuntary or visceral nervous system.

Function of ANS

Regulate and integrate the body's internal functions with little conscious awareness of its activity.

Main Nerve Centers for the ANS

Hypothalamus, Adrenal Medulla, Spinal Cord.

Afferent Impulses

Receives impulses in.

Efferent Impulses

Send impulses out.

Ganglia

Group of nerve bodies located outside the spinal column.

Divisions of the ANS

The ANS is divided into two branches: Sympathetic (Adrenergic) and Parasympathetic (Cholinergic).

Sympathetic Division

Originates from the thoraco-lumbar region.

Parasympathetic Division

Originates from the craniosacral region.

Sympathetic Neurons

Short preganglion and long postganglion.

Parasympathetic Neurons

Long preganglion and short postganglion.

Synapse

Space between two neurons.

Neurotransmitters

Special chemicals utilized in synaptic transmission.

Catecholamines

Neurotransmitters including Epinephrine, Norepinephrine, Serotonin, and Dopamine.

Acetylcholine

Neurotransmitter used in the parasympathetic division, stored in presynaptic granules.

Bodily Functions Regulated by the ANS

Includes Blood Pressure, Heart Rate, Respiration, Body Temperature, Water Balance, Urinary Excretion, Digestive Functions, Uterine contractions.

Fight or Flight Response

Activation of Sympathetic Nervous System leading to increased heart rate and blood pressure.

Adrenergic Response

Norepinephrine synthesis and storage made from tyramine.

Adrenergic Receptors

Types include Alpha1, Alpha2, Beta1, and Beta2.

Norepinephrine Reuptake

Termination of response by uptake of norepinephrine by nerve terminal.

Monoamine oxidase (MAO)

Systemic enzymes that break down norepinephrine.

Catechol-O-methyl transferase (COMT)

Systemic enzymes that break down norepinephrine.

Alpha1 Receptors

Located in blood vessels, they cause vasoconstriction and increase peripheral resistance, raising blood pressure.

Alpha1 Receptors in the Iris

Cause pupil dilation.

Alpha1 Receptors in the Urinary Bladder

Cause the increased closure of the internal sphincter.

Alpha2 Receptors

Located in nerve membranes, they act as modulators of norepinephrine release.

Alpha2 Receptors in Beta Cells

Help to moderate the insulin release stimulated by SNS activation.

Beta1 Receptors

Located in cardiac tissue, they can stimulate increased myocardial activity and increased heart rate.

Beta1 Receptors Function

Responsible for increased lipolysis or breakdown of fat for energy in peripheral tissues.

Beta2 Receptors

Located in smooth muscle in blood vessels, stimulation leads to vasodilatation.

Beta2 Receptors in Bronchi

Can cause dilation.

Beta2 Receptors in Periphery

Increased muscle and liver breakdown of glycogen and increased release of glucagon.

Beta2 Receptors in Uterine Muscle

Results in relaxed uterine smooth muscle.

Sympathetic Nervous System (SNS)

Originates from thoracolumbar region, has short preganglionic fibers, and long postganglionic fibers.

Preganglionic Fibers in SNS

Release acetylcholine.

Postganglionic Fibers in SNS

Release epinephrine and norepinephrine at end organ synapse.

Adrenal Medulla

Secretes epinephrine and norepinephrine directly into blood system.

Parasympathetic Nervous System (PNS)

Increases motility and secretions in the GI tract, decreases heart rate and contractility.

Cholinergic Nerves

All preganglionic nerves in the ANS, both sympathetic and parasympathetic.

Muscarinic Receptors

Stimulated by muscarine, found in visceral effector organs and sweat glands.

Nicotinic Receptors

Located in the CNS, adrenal medulla, autonomic ganglia, and neuromuscular junction, stimulation causes muscle contraction.

Autonomic Tone

Balance between sympathetic and parasympathetic systems, usually parasympathetic is in control when resting.

Vasomotor Tone

Blood vessels innervated only by sympathetic nerves; more sympathetic innervation means more vasoconstriction.

Difference between SNS and PNS

B. The location of the nerve ganglia.

Location of the nerve ganglia

The specific anatomical position where nerve ganglia are situated.

Types of nerves

Preganglionic, Postganglionic, Motor, Sensory, and Presynaptic nerves.

Sympathetic stress reaction

A physiological response characterized by increased heart rate, dilated pupils, and elevated blood pressure.

Beta 2 receptors stimulation

Indicated by findings such as bronchial dilation and increased myocardial contraction.

Adrenergic Agonists

Drugs that mimic the effects of the sympathetic nervous system.

Therapeutic effects of Adrenergic Agonists

Effects related to their stimulation of adrenergic receptor sites.

Uses of Adrenergic Agonists

Varies from ophthalmic preparations for dilating pupils to systemic preparations used for shock.

Classification of Adrenergic Agonists

Adrenergic agonists may be classified as catecholamines or noncatecholamines.

Administration of Catecholamines

Cannot be given orally; must be administered parenterally or by inhalation.

Blood-brain barrier and Catecholamines

Catecholamines do not cross the blood-brain barrier.

Agonist

A substance that activates a receptor to produce a biological response.

Antagonist

A substance that blocks or dampens the biological response by binding to a receptor.

-lytic

A suffix indicating a drug that inhibits or blocks a physiological response.

-mimetic

A suffix indicating a drug that mimics a physiological response.

Physiological Responses of Adrenergic Agonists

Responses include increased heart rate, bronchial dilation, and other sympathetic effects.

Rationale for nerve classification

Nerves differ in location of originating cells in the CNS, location of nerve ganglia, and types of neurons.

If you suspect that a person is very stressed and is experiencing a sympathetic stress reaction, you would expect to find:

Dilated pupils and elevated systolic blood pressure

Constricted pupils and warm, flushed skin

Expected findings in a person experiencing a sympathetic stress reaction.

Slow heart rate and decreased systolic blood pressure

Expected findings in a person experiencing a sympathetic stress reaction.

Dilated pupils and elevated systolic blood pressure

Expected findings in a person experiencing a sympathetic stress reaction.

Noncatecholamines

May be taken orally (PO), not destroyed as readily by MAO or COMT, better able to enter brain and affect CNS.

Sympathomimetics

Direct stimulation of receptors, release of neurotransmitters from neuron, inhibiting reuptake of NE from synapse (antidepressants, cocaine), preventing destruction of NE: MAOI, COMT inhibitors.

Alpha agonist

A type of adrenergic agonist that primarily stimulates alpha receptors.

Beta agonist

A type of adrenergic agonist that primarily stimulates beta receptors.

Dopamine (generic)

Used for shock.

Dobutamine (generic)

Used for congestive heart failure.

Epinephrine (Adrenalin, Adrenaclick)

Used for shock, glaucoma, and prolongs effects of regional anesthetic.

Norepinephrine (Levophed)

Used to treat shock or during cardiac arrest to get sympathetic activity.

Ephedrine (generic)

Used for seasonal rhinitis and hypotensive episodes.

Prototype: Dopamine

Stimulates heart and blood tissue, arteriole dilation of renal and splanchnic vessels, renal protective.

Effects of Alpha and Beta Agonists

Increased heart rate, strength of contractions, blood vessels constrict: BP, decreases intraocular pressure, pupils dilate, glycogenolysis, increased sweating.

Adverse Effects of Alpha- and Beta-Adrenergic Agonists

Arrhythmias, hypertension, palpitations, angina, dyspnea, nausea, vomiting, headache, sweating, tension, anxiety.

Drug-Drug Interactions

Tricyclic antidepressants and MAOIs, other drugs causing hypertension, caffeine containing products.

Nonselective Adrenergic Agonists

Prototype drug: Epinephrine (Adrenalin), therapeutic classification: antishock and antianaphylaxis agent, bronchodilator.

Epinephrine (Adrenalin) for Cardiac Arrest

1:10,000 (0.1 mg/mL) for cardiac arrest.

Epinephrine (Adrenalin) for Anaphylaxis

1:1,000 (1 mg/mL), prefilled syringe with 0.3 mg, MR X1 in 5-15 min prn.

Alpha-Specific Adrenergic Agonists

Drugs that bind primarily to alpha-receptors rather than to beta-receptors.

Phenylephrine (Neo-Synephrine)

Vasoconstrictor with little cardiac or respiratory effects, used for allergy products, rebound congestion, and to dilate pupils.

Clonidine (Catapres)

Stimulates alpha 2 receptors, decreases sympathetic outflow from CNS, treats hypertension.

Midodrine (ProAmatine)

Used to treat orthostatic hypotension.

Contraindications for Alpha-Specific Adrenergic Agonists

Known allergy, severe hypertension or tachycardia, narrow-angle glaucoma, pregnancy.

Adverse Effects of Alpha-Specific Adrenergic Agonists

Anxiety, restlessness, depression, fatigue, blurred vision, ECG changes, arrhythmias, blood pressure changes.

Nursing Considerations for Alpha-Specific Adrenergic Agonists

Do not discontinue abruptly; taper over 2-4 days, monitor orthostatic BP.

Question #1

Please identify the following statement as true or false.

Contraindications for Alpha- and Beta-Adrenergic Agonists

Pheochromocytoma, tachyarrhythmias or ventricular fibrillation, hypovolemia, halogenated hydrocarbon general anesthetics.

Nursing considerations

Use extreme caution in calculating doses, monitor heart rate, BP, and urine output carefully.

Prototype drug: Epinephrine (Adrenalin)

Therapeutic classification: Antishock and antianaphylaxis agent, bronchodilator.

Epinephrine dosage for Cardiac arrest

1:10,000 (0.1 mg/mL).

Epinephrine dosage for Anaphylaxis

1:1,000 (1 mg/mL), prefilled syringe with 0.3 mg, MR X1 in 5-15 min prn.

Adverse effects of Epinephrine

Nervousness, tremors, palpitations, tachycardia, dizziness, headache, stinging at site.

Serious adverse effects of Epinephrine

HTN, dysrhythmias, pulmonary edema, cardiac arrest, intense CNS stimulation.

Indications for Alpha-Specific Adrenergic Agonists

Orthostatic hypotension, constriction of topical vessels in nose, dilate pupils.

Drugs in Alpha-Specific Adrenergic Agonists Class

Phenylephrine (Neo-Synephrine), Midodrine (generic), Clonidine (Catapres).

Drug-Drug Interaction for Alpha-Specific Adrenergic Agonists

MAOIs and TCAs, digoxin, beta-blockers, antipsychotics.

True or False Question

Another name for an adrenergic agonist drug is a sympathomimetic drug.

Adrenergic Agonist

Also called a sympathomimetic drug because it mimics the effects of the sympathetic nervous system (SNS).