Autonomic Control Of The CVS Flashcards
Sympathetic and parasympathetic effect and receptors: pupil of the eye
Dilation a1
Contraction M3
Sympathetic and parasympathetic effect and receptors: airways of lungs
Relax B2
Contract M3
Sympathetic and parasympathetic effect and receptors: heart
Increase rate and force of contraction B1
Decrease rate M2
Sympathetic and parasympathetic effect and receptors: sweat glands
Localised secretion a1
Generalised secretion M3
No effect for parasympathetic
The ANS controls…
Heart rate, force of contraction of heart, peripheral resistance of blood vessels, amount of venoconstriction
Where does the parasympathetic input to the heart arise from?
10th (X) cranial nerve
Vagus
Where does the parasympathetic input to the heart synapse?
Postganglionic cells on epicardial surface or within walls of heart at SA and AV node
What do postganglionic cells release and which receptors do they act on? What is the effect on the heart?
ACh
M2
- decrease heart rate (-ve chronotropic effect)
- decrease AV node conduction velocity
Which part of the heart do the sympathetic fibres innervate and what do they release? Which receptors?
SA node, AV node and myocardium
Release noradrenaline
B1 adrenoceptors
What effect does the sympathetic nervous system have on the heart?
Increases heart rate (+ve chrontropic effect)
Increases force of contraction (+ve inotropic effect)
Where are the baroreceptors located in the heart?
Carotid sinus
Arch of aorta
How does noradrenaline increase force of contraction?
Binds to B1 receptors
cAMP stimulates PKA, which phosphorylates calcium channels at plateau of AP
Allows flow of Ca2+ into cell
CICR and increased uptake of Ca2+ into ER
Increased sensitivity of contractile machinery to Ca2+
Which receptors do most arteries and veins have?
Alpha1 adrenoceptors
Coronary and skeletal muscle vasculature also have β2 receptors
Which receptors do adrenaline and noradrenaline bind to?
Adrenaline has a higher affinity for B2 adrenoceptors, but will also bind to a1 adrenoceptors at higher concentrations
Activating β2 adrenoreceptors
Causes vasodilation
Increases cAMP -> PKA -> opens potassium channels + inhibits MLCK -> relaxation of smooth muscle
Activating a1 adrenoceptors
Causes vasoconstriction
Stimulates IP3 production
Increase in [Ca2+]in from stores and via influx of extracellular Ca2+ -> contraction of smooth muscle
Baroreceptors
Increased arterial pressure stretches these receptors.
Important for maintaining blood pressure over short term.
Can re-set to higher levels with persistent increases in blood pressure.
Clinical application: drugs acting on the ANS
Sympathomimetics
Adrenoceptor antagonists
Cholinergics
Sympathomimetics
Administration of adrenaline to restore function in cardiac arrest
B1 agonists - dobutamine may be given in cardiogenic shock (pump failure)
Adrenaline administered for anaphylactic shock
Adrenoreceptor antagonists
α-adrenoreceptor antagonists - prazosin, anti hypertensive agents
β-adrenoreceptor antagonists - propranolol (non selective B1/B2 antagonist, slows heart rate and reduces force of contraction, but also bronchoconstrictor - B2), atenolol selective B1
Cholinergics
Muscarinic agonists - e.g. pilocarpine, used in treatment of glaucoma, activates constrictor pupillae muscle
Muscarinic antagonists - e.g. atropine or tropicamide, increases heart rate, bronchial dilation, used to dilate pupils for examination of the eye
