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Autonomic Nervous System
regulates visceral functions that occur without conscious control; all visceral organs except skeletal muscle
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ANS orginates from _____ (_____ and ____ ____) and divided into two parts:
CNS, brain, spinal cord
- 1. Parasympathetic
- 2. Sympathetic
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autonomic ganglia
specialized complex structures residing outside the spinal cord that contain axodendritic synapses between preganglionic and postganglionic neurons
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Types of Neurotransmitters
Acetylcholine
Norepinephrine
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Acetylcholine is synthesized in the ____ from _________ and _____ by ______ _____________
neurons, acetyl CoA, choline, choline acetyltransferase
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Acetylcholine is broken down in the ______ _________ or the ______-______ _________ by _________ ______
ganglionic junction, neuro-effector junction, acetylcholine esterase
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ACh's effects are mediated through two subtypes of receptors
1. Muscarinic (M) receptors: present in the neuro-effector junction of the parasympathetic division
2. Nicotinic (N) receptors: present in the autonomic ganglia of both and the neuro-muscular junction
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NE and epinephrine are mediated by two receptor subtypes:
alpha receptors: alpha1, alpha2
beta receptors: beta1, beta2
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alpha 1 receptors
present in the arteriolar smooth muscles. Activation leads to vasoconstriction (blood vessels), increase blood pressure
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alpha 2 receptors
found pre-gangionically and in the CNS. Activation leads to decrease in the sympathetic flow from CNS
NOT post-synaptic
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beta 1 receptors
found in the heart and kidney. Activation leads to increase HR, foce of contraction, and release of renin from kidney causing hypotension, stimulate heart
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beta 2 receptors
found in smooth muscles of blood vessels and bronchi. Activation leads to vasodilation and bronchodilation. Important in lungs
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Direct-Acting Parasympathomimetics
stimulation of M receptors at the neuro-effector junction with little or no N receptor stimulation
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Indirect-Acting Parasympathomimetics
these agents do not stimulate the M receptors but prolong the duration of action of endogenous ACh by inhibiting ACh esterase, the enzyme that breaks down ACh
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Neostigmine
a carbamate, reversible inhibitor of ACh esterase; used as a ruminatoric (given to cows to stimulate digestion)
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Paraxon, Malaoxon
organophosphorus insecticides, irreversible ACh esterase inhibitors; no therapeutic use
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Serious toxic reactions to muscarinic agonists can be treated with _________
atropine sulfate (SQ or IV)
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Mechanism of Action of Muscarinic Receptor Antagonists
competitive blocking of muscarinic receptors at the neuro-effector sites on smooth muscle, cardiac muscle, gland cells, in the CNS with little blockade of the effects of ACh at nicotinic receptor sites
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Blocking Muscarinic Receptors (Antagonists) causes:
drying of secretions, inhibit digestion, increase heart rate, inhibit sweating
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Muscarinic Receptor Agonists and their therapeutic uses
Atropine: stimulate heart by blocking vagus nerve; used during surgery to dry secretions
aminopetamide: dry secretions
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Endogenous sympathomimetic drugs include
epinephrine (adrenaline), norepinephrine (noradrenaline), dopamine
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Epinephrine- Pharmacological Effects
beta1: increase heart rate
beta2: bronchodilator
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Norepinephrine- Pharmacological Effects
more powerful activator of alpha1 receptors than epinephrine, weaker activaor of beta2 receptors
increases blood pressure; not useful bronchodilator
can be used to treat hypotension
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Dopamine- Pharmacological Effects
at low doses, activation of D1-receptors in the renal, coronary, and mesentric beds lead to vasodilation
at higher doses, dopamine can stimulate cardiac beta1 receptors leading to a positive inotropic and chronotropic effects
used in treatment of severe CHF
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Non selective beta agonists
include: epinephrine, ephedrine, isoprotrenol
used in emergencies to stimulate heart rate in cases with bradycardia or heart block
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Beta2 Selective Agonists
Terbutaline; in treatment of asthma (allergic or exercise)
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alpha1 selective agonists
- -nasal decongestants in humans
- -constrict bood vessels in nasal tissues leading to decreased blood flow, decreased fluid accumulation in nasal tissues
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alpha2 selective agonists
includes: xylazine, detomidine, and Medetomidine
decrease in central sympathetic activity which give sedation and analgesia, they produce good muscle relaxation
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alpha-adrenoceptor blockers
used primarily in humans to lower blood pressure
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beta-adrenergic receptor blockers
blocking of beta1 receptors leads to slowing of heart rate and decreasing myocardial contractility
blocking of beta2 receptors has little effects on pulmonary function, bronchoconstriction
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non selective beta-blockers
reversibly block beta1 and beta2 receptors with no selectivity towards either subtype; propranolol
-carvedilol: some alpha1 blocking activity to decrease blood pressure
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beta1 selective blockers
metoprolol, acebutolol
do no affect the lungs
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