Autonomic Nervous System

2 divisions in balance

Parasympathetic – The slow division of ANS, opposite ‘fight of flight reactions’

Sympathetic – The fast division, ‘fight or flight’ response

Body Parts affected :

Sympathetic Stimulation	Parasympathetic Stimulation
Dry Mouth	Salivation
Pupillary Dilatation	Pupillary Constriction
Increased Cerebral Circulation	Decreased Cerebral Circulation
Bronchodilation	Bronchoconstriction
Increased Heart Rate(Chronotropism)	Decreased Heart Rate
Increased Contractibility(Inotropism)	Decreased Contractibility
Increased Irritability	Decreased Irritability
Increased AV-Node Conduction(Dromo)	Decreased AV-Node Conduction
Decreased Digestion	Increased Digestion
Increased Skeletal Muscle Circulation	Decreased Skeletal Muscle Circulation

Cardiac Concepts of the Autonomic Nervous System

Myocardium consists of special muscle tissue. Directly stimulated to contract by

nerves in heart.

Chronotropism(chronotropic action) - Frequency of contraction(time)

Inotropism(Inotropic action) - Strength or vigor of contraction

Dromotropism(Dromotropic action) – Effects conduction time through the

Atrio-ventricular node(gate to ventricles)’AV Node’

Blood Pressure Changes

Baroreceptors – located in carotid arteries and aorta senses pressure in the

Vessels, if pressure or stretch is too high impulses are sent to the brain stem

back via vagus nerve to signal heart to reduce rate and contractability

Peripheral vasculature – The pipes(arteries & veins)from heart under control ANS

The walls are supplied with smooth muscle cells which contract or relax

When stimulated by ANS. What occurs in the ‘pipes’ very much effects

Performance of heart

Peripheral resistance – Resistance to the flow of blood,

How much blood is flowing, how thick(viscous) the blood.

Most importantly the diameter of the vessel

ANS response regulation – 2 nerve fibers connected by a bridge

Bridge – ganglion has a synapse (gap) between the fibers

After the synapse is the ‘post-ganglionic’ fiber which travels to organ or blood vessel to produce effect

Sympathetic Nerve Fibers – Sympathetic nerves arise from thoracic 1 to lumbar 2 in spine

The preganglion fiber is short(important because of fight or flight) short way to travel

Postganglion is far

Parasympathetic Nerve Fibers – Arise from the brain stem and sacral portions of cord

Vagal Nerve – Vagus(wondering one) – wonders all the way to stomach before synapse

In ganglion

Block or severe vagus nerve sympathetic functions increase

ANS Nerve transmitters

ANS controlled by naturally occurring chemical transmitters that carry messages across synapse

Each division has specific chemical receptors that are associated w/ specific chemical response

Parasympathetic Transmission – Acetylcholine à Acetylcholine

Sympathetic Transmission – Acetylcholine à Norepinephrine

2 ways to modify effects of both divisions ganglia and end-organ synapses

Administer the transmitter chemical into body: EX: synthetic norepinephrine à levophed

Block the chemical transmission within ganglion or never organ ending

Preganglionic impulse ‘breaks’ little packs of ACh(Acetylcholine) then reacts by being

taken across the gap by the post-synaptic membrane.

A nerve impulse is then initiated down post-ganglionic fiber

Acetylcholinesterase – Enzyme that breaks down ACh located in post-synaptic region

To prevent repeated stimulation

Nerves whose impulses are mediated by Acetylcholine are called cholinergic

Nerves whose impulses are mediated by norepinephrine are called adrenergic

Sympathetic Division of ANS has 2 types of receptors or receiver cells that are stimulated by norepinephrine and other natural catecholamines epinephrine and dopamine

Alpha – located in smooth arterial walls

Beta 1’s – located in heart

Beta 2’s – located in peripheral tissue (blood vessels and bronchioles of lungs)

Alpha receptors constrict smooth muscle of arterial walls

Beta receptors dilate smooth muscles(bronchioles and arterioles)

Blocking Alpha à Vasodilation : Stimulating Alpha à Vasoconstriction

Blocking Beta 2 à Vasoconstriction : Stimulating Beta 2 à Vasodilation

All Alpha receptors in the heart cause positive inotropic action and negative chronotropic

Beta 1 receptors in heart when stimuled:

Increase Rate (positive chronotropic)

Increase Force (positive inotropic)

Increase A-V Node Conductivity(positive dromotropic)

Have dilating effect on coronary vessels

Increase ectopic activity – I.E. Irritability

Beta 2 receptors in arterioles lead to dilation of vascular bed and yield fall in bp

General idea to manipulate system in shock ex: MI or cardiogenic shock

Obtain proper balance between Beta 1 effects with slight alpha effect to maintain BP

3 Natural chemicals act on the sympathetic system – ‘Catecholamines’

Dopamine, Epinephrine, Norepinephrine

Natural chemicals give both alpha and beta effects

Using clinically the goal is to balance them in order to obtain good cardiac output

Epinephrine secreted naturally by adrenal gland – 80% epinephrine 20% norepinephrine

Beta Stimulation

Stimulating Beta 2’s is useful for treatment of bronchioconstriction. I.e. anaphylaxis or asthma

Albuterol is a beta 2 agonist, dilates bronchioles but effects beta 1 with tachycardia

Beta Blockers

Only one drug used in pre-hospital setting as beta blocker, metoprolol(generic) lopressor(trade)

Beta Stimulation	Beta Blocking
Increased Heart Rate	Decreased Heart Rate
Increased Contractibility	Decreased Contractibility
Increased AV-node Transmission	Decreased AV-node Transmission
Increased Irritability	Decreased Irritability

Using beta blockers is useful when it is necessary to reduce contractibility, i.e. anginal pain

Alpha Stimulation

Ex: Neosynepherine a pure alpha stimulator; the spray constricts the vessels in the nasalmucosa

(an Alpha – peripheral vasodilator effect)

Parasympathetic Manipulation

Blocking the parasympathetic system causes sympathetic to dominate causing fight or flight.

Any drugs used to block or inhibit the parasympathetic division are parasympatholytic drugs

Lytic-break up

Ex: Atropine acts by preventing the uptake of the transmitting chemical at parasympathetic nerve ends

Atropine Indications for Use:

· Hemodynamically significant symptomatic bradycardia

· Sinus arrest or block

· AV block at Junctional level

· PEA or Asystole

· Organophosphate poisoning, cholinesterase inhibiting pesticides, serine, parathion and gas poisons

Atropine Mechanism of Action:

· Increases myocardial O₂ demand

· Blocks effects of acetylcholine

· Increases rate of discharge at SA and AV nodes

· Relaxes smooth muscle in GI tract

· Inhibits secretions of duct glands (sweat and saliva)

· Causes relaxation of smooth muscle in bronchial tree