the nervous system

The Nervous System

Central Nervous System

Peripheral Nervous System

Somatic Nervous System

Autonomic Nervous System

DIVISIONS OF NERVOUS SYSTEM

The Central Nervous System(CNS)Consists of the brain and spinal cord

Regulates body functionsInterprets information sent by the

peripheral nervous system (PNS ) and then sends stimuli back to the PNS

Peripheral Nervous System

Somatic NS – acts on skeletal muscles to produce locomotion & respiration

Autonomic NS – visceral system; controls and regulates functioning of the heart, respiratory system, digestive system & glandsSympathetic nervous system Parasympathetic nervous system

Features of Autonomic Nervous System

2 neuron system Synaptic transmission

Synapse- space between neurons or between neuron and its target organ

Presence of Ganglion/ganglia Ganglia – collection of nerve cell bodies outside

CNS

Comparison of SNS and PSNS

SYMPATHETIC PARASYMPATHETIC

Origin of fibers

Thoracolumbar Craniosacral

Length of fiber

Preganglionic: short

Postganglionic:long

Long

Short

Receptors Alpha, beta, dopamine

Muscarinic, Nicotinic

NT NE, EPI, dopamine Acetylcholine

Responses

General

“Fight, flight, fright” “Rest and digest”

Receptors

1. Nicotinic receptors are located on the cell bodies of all postganglionic neurons of the PSNS and SNS (& adrenal medulla)

2. Muscarinic receptors are located in all organs regulated by the PSNS

3. Adrenergic receptors are located in all organs regulated by SNS except sweat glands

Neurotransmitters

1. All preganglionic neurons of the PSNS and SNS release ACh as their transmitter.

2. All postganglionic neurons of the PSNS release ACh as their transmitter.

3. Most postganglionic neurons of the SNS release NE

4. EPI is the principal transmitter released by adrenal medulla

5. All motor neurons to skeletal muscles realese ACh as their transmitter

The Sympathetic NS

Fight or flight response– “the bear” – prepares the body for stress by increasing metabolism, diverting blood to larger muscles and increasing cardiac and respiratory functions

The Parasympathetic NS

Rest and digest response – increases digestion, absorption and slows metabolism to save energy – “the pig”

SNS vs. PNS Effects on Tissues

SNS Effects Dilates pupils Relaxes smooth

muscles of the GIT Dilates bronchioles Increases heart rate Constrict blood

vessel Relaxes bladder &

uterine muscle

PNS Effects Constricts pupils Increases peristalsis Constricts

bronchioles & increases secretions

Decreases heart rate

Dilates blood vessels

Increases salivation

Sympathetic Nervous System

Also called the adrenergic system (adrenaline) The neurotransmitter is norepinephrine Drugs that mimic the effects of norepinephrine are the

adrenergics, sympathomimetics or adrenomimetics Because they initiate a response they are called

adrenergic agonists Drugs which block the SNS are called sympatholytics

or adrenolytics, anti-adrenergics and the alpha and beta adrenergic blockers; because they block a response, they are adrenergic antagonists

Parasympathetic Nervous System

Also called the cholinergic system The neurotransmitter is acetylcholine Parasympathomimetics, cholinomimetics and

cholinergics stimulate the PNS Called cholinergic agonists because they

initiate a cholinergic response Parasympatholytics, anticholinergics and

cholinergic blocking drugs inhibit the PNS; called cholinergic antagonists because they block a response

Comparison of SNS & PNS Drugs

Sympathetic Response–“the bear”

Agonist Sympathomimetics Adrenergic drugs

Antagonist Sympatholytics Adrenergic blockers

Parasympathetic Response – “the pig”

Agonist Parasympathomimetic Cholinergic drugs

Antagonist Parasympatholytic Anticholinergic drugs Cholinergic blockers

Functions of Peripheral Adrenergic Receptor

Alpha 1 Eye Mydriasis

Arterioles Constriction

Sex organ, male EjaculationBladder neck, prostatic capsule Contraction

Alpha 2 Presynaptic nerve terminal Blocks NE release

Beta 1 Heart +Inotropic,Chronotropic, dromotropic

Kidney Renin release

Beta 2 Arterioles Dilation

Bronchi Dilation

Uterus Relaxation

Liver Glycogenolysis

Adrenergic Drugs: Review

Act on adrenergic receptor sites on the cells of smooth muscles

Adrenergic receptorsAlpha1 – vasoconstriction; increases cardiac

contraction; mydriasis, bladder neck and prostatic capsule contraction

Alpha2 – inhibits norepinephrine, dilates blood vessels; decreases GIT tone & motility

Beta1 – increases rate & force of cardiac contraction; increases renal secretion of renin, increasing BP

Beta2 – dilates bronchioles; glycogenolysis; increases skeletal muscle blood flow; GIT/uterine relaxation

Catecholamines

The chemical structures of a substance, either endogenous or synthetic, that can produce a sympathomimetic response

EndogenousDopamine, epinephrine & norepinephrine

Synthetic isoproterenol, dobutamine

Indications of Adrenergic Drugs

Emergency drugs – inotropic drugs, vasopressors Cardiac arrest, hypotension, heart failure Asthma, URT congestion – bronchodilation,

vasoconstriction Allergies, bleeding – vasoconstriction Hypoglycemia – glucogenolysis Obstetric use – stops premature labor Eye disorders – causes pupil dilation

Not for patients with glaucoma Used with local anesthetics – vasoconstriction

Adrenergic Drug: Epinephrine

Epinephrine (Adrenaline Cl) acts indirectly by stimulating release of norepinephrine which acts directly on adrenergic receptor sites

Can be given IV, IM, topical, inhalation or SQ Used to fight anaphylaxis; rapid onset of action Potent inotropic drug; may reduce renal

perfusion Nurses must monitor vital signs carefully

and watch for rapid heart rate, dizziness and increased blood pressure; ECG monitoring

Isoproterenol HCl (Isuprel)

Bronchodilation & increase in heart rateCan cause severe tachycardiaOften used to treat asthma

Albuterol (Proventil, Ventolin)

Produces rapid bronchodilationUsed to treat bronchospasmsSE: tachycardia, tremors, restlessness,

nervousnessCaution: taken with mono amine

oxidase inhibitors (MAOI), may cause hypertensive crisis

Clonidine (Catapres) & Methyldopa (Aldomet)

Alpha2 adrenergic drugsTreats hypertension by regulating /

inhibiting the release of norepinephrine May cause cardiovascular depression by

stimulating alpha2 receptors in the CNSSE: tachycardia, palpitations,

dysrrhythmia, n/v, urinary difficulty, tremors, dizziness

Nursing Responsibilities

Frequent VS monitoring Check urinary output, bladder distention Check for IV infiltration. Norepinephrine & dopamine

may cause tissue necrosis. Antidote is Phentolamine mesylate (Regitine)

Take with food to prevent N/V. Monitor labs – may increase glucose level

Glycogenolysis Read OTC labels: cold medicines, diet pills Rebound nasal congestion may occur. DO NOT give to nursing mothers.

Adrenergic Blockers

Blocks the effects of neurotransmitters Alpha blockers cause a decrease in blood

pressure, orthostatic hypotension Beta blockers decrease heart rate and force of

cardiac contraction, cause bronchoconstriction Used in HTN, PVD, Raynaud’s disease,

dysrhythmias Monitor HR, BP Use with caution in patients with COPD

Adrenergic Blockers

Alpha 1 blockersPrazosin HCl (Minipress), Doxazosin HCl (Cardura),

Terazosin HCl (Hytrin)

Alpha 1, Beta 1 & 2 blockersCarvedilol (Coreg), Labetalol (Trandate)

Beta 1 blockersMetoprolol tartrate (Lopressor), Atenolol (Tenormin)

Beta 1 & 2 blockersPropanolol (Inderal), Nadolol (Corgard)

Nursing Responsibilities

VS monitoring; ECG for baselineAssess for respiratory problemsObserve for and prevent orthostatic

hypotensionAdvise clients to avoid abruptly stopping

a beta-blocker & to monitor blood sugarDose-related changes in male sexual

function may occur

Cholinergic Drugs

Cholinergic stimulants, cholinergic agonists, parasympathomimetics - they mimic acetylcholine

Stimulate the PNS. Major action is to stimulate bladder and GI tone, constrict pupils (miosis) and increase neuromuscular transmissions to receptor sites

Acetylcholine (ACh) – neurotansmitter located at the ganglions and parasympathetic nerve endings

Two cholinergic receptors: Muscarinic receptors – stimulate smooth muscle

(eye, GIT, urinary system) and slow heart rate Nicotinic receptors - affect skeletal muscle

Acetylcholine (ACh) & Cholinesterase (ChE)

Acetylcholine (ACh) - neurotransmitter Cholinesterase (ChE) – promotes breakdown

of ACh

Cholinesterase destroys acetylcholine.

More cholinesterase, less acetylcholine available.

Inhibit cholinesterase, more acetylcholine available.

Direct-acting Cholinergics

Bethanecol (Urecholine) – increases urination

Metoclopramide HCl (Reglan) – treats gastro-esophageal reflux disease (GERD) by increasing gastric emptying time

Pilocarpine – causes miosis; used in treating glaucoma

Bethanechol Cl (Urecholine)

Treats urinary retention and abdominal distention; promotes micturition and increases peristalsis in the GIT

Poorly absorbed in the GIT. Given on empty stomach. Voiding occurs 30 minutes – 1 ½ hrs after po

administration and 15 minutes after SC SE: N/V, hypotension, bradycardia,

diarrhea, salivation, sweating, flushing, frequent urination, rash, miosis, blurred vision

Contraindication: intestinal or urinary tract obstruction, asthma

Reversible Cholinesterase Inhibitors

Produces miosis to treat glaucoma Increases muscle strength in myasthenia

gravis Neostigmine (Prostigmine), Pyridostigmine bromide

(Mestinon), Edrophonium Cl (Tensilon)

CAUTION: bradycardia, asthma, PUD, hyperthyroidism

CONTRAINDICATION: intestinal / urinary tract obstruction

Nursing Responsibilities

Assess urine output, bowel & breath sounds Assess for asthma, PUD, urinary & intestinal

obstruction Monitor BP, pulse – orthostatic hypotension Give 1 hour ac or 2 hours pc Check serum lipase, amylase Cholinergic overdose: sweating, salivation,

flush, abdominal cramps Antidote: Atropine sulfate (0.6mg)

Anticholinergics

Parasympatholytics, cholinergic blocking agents

They inhibit the actions of acetylcholine Major responses are to decrease GI motility

and salivation, to dilate pupils and to increase pulse rate; may cause decreased bladder contraction

Used to treat the early stages of Parkinson’s disease and to decrease tremors and rigidity & to decrease salivation and drooling

CONTRAINDICATION: Glaucoma

Atropine sulfate

Derived from the belladonna plant Vagolytic – inhibits vagal stiumulation Used as a pre-op med, anti-spasmodic,

treatment of bradycardia; for mydriasis & cycloplegia

Give IV undiluted or with 10 cc sterile water at 0.6 mg/min

SE: dry mouth, decreased perspiration, blurred vision, tachycardia, constipation, urinary retention

Glaucoma & Anti-cholinergics

Anticholinergic Drugs

BelladonaHyoscyamine sulfate Scopolamine hydrobromide

Patch used for prevention of n/v among adults with motion sickness

Antiparkinson - Anticholinergic Drugs

Used to treat the early stages of Parkinson’s disease and to decrease tremors and rigidity & to decrease salivation and drooling

Used in the treatment of pseudoparkinsonism in psychotropic drugs

Trihexyphenidyl HCl (Artane) Biperiden HCl (Akineton) Benztropine mesylate (Cogentin)

Nursing Responsibilities

Assess PR, UO, bowel sounds Encourage void before taking medication Maintain adequate fluid intake Encourage to eat foods high in fiber Encourage activity. Avoid hot environment. Oral care. Ice chips. Hard candy. Avoid caffeine, alcohol, cigarettes, aspirin

before bedtime Safety precautions – drowsiness is common

Anti-spasmodics

Anticholinergic, atropine-like drugs Dicyclomine (Bentyl)Propantheline bromide (Pro-banthine)Toleterodine (Detrol) Glycopyrrolate (Robinul)

Secretory inhibitor Oxybutynin (Ditropan)

Urinary antispasmodic