the nervous system
TRANSCRIPT
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