Autonomic Nervous System Flashcards
What effects does the sympathetic nervous system have on the heart
Sympathetic input to the heart from postganglionic fibres from the sympathetic trunk
Innervate SA node, AV node and myocardium
Release noradrenaline
Acts mainly on ß1 adrenoceptors - increase heart rate (positive chronotropic effect), increases force of contraction (positive inotropic effect)
What effects does the parasympathetic nervous system have on the heart
Parasympathetic input to the heart from preganglionic fibres - 10th cranial nerve - vagus
Synapse with postganglionic cells on epicardial surface or within walls of heart at SA and AV node
Postganglionic cells release acetylcholine
Acts on M2 receptors - decrease heart rate (negative chronotropic effect), decrease AV node conduction velocity
What controls the levels of sympathetic and parasympathetic input
Medulla oblongata
What do baroreceptors do?
Measure blood pressure and send inputs to cardiovascular center in medulla oblongata
How does sympathetic activity alter the SA action potential slope and what is the effect of this
Increases slope - increases heart rate
Mediated by ß1 receptors - G protein receptors (Gs) increases cAMP and speeds up pacemaker potential
How does parasympathetic actvity alter the SA action potential slope and what is the effect of this
Decreases slope - slow down rate of depolarisation
Mediated by M2 receptors - G protein receptors (Gi) reduces cAMP produced and increase potassium conductance
How does noradrenaline increase force of contraction
Noradrenaline acts on ß1 receptors in myocardium causing an increase in cAMP activating PKA
Phosphorylation of calcium channels increase calcium entry during plateau of the action potential
Increased uptake of calcium in SR
Increased sensitivity of contractile machinery to calcium
What receptor is located on most arteries and veins
Most arteries and veins have α1-adrenoreceptors
Coronary and skeletal muscle vasculature also have ß2-receptors
When is α1 or ß2 receptors preferentially activated
ß2 adrenoceptors more sensitive to circulating adrenaline
Exercise, stress
Adrenaline preferentially binds to ß2
Causes vasodilation - increases cAMP -> PKA -> opens potassium channels + inhibits MLCK -> relaxation of smooth muscle
Noradrenaline from sympathetic activates α1
At high concentration of adrenaline, such as in shock of adrenaline, activates α1 instead to cause vasoconstriction
Causes vasoconstriction - increase in cytosolic calcium concentration from stores and via influx of extracellular Ca2+ -> contraction of smooth muscle
Also stimulates IP3 production
Explain the effect of metabolites on tissue
Eg. Adenosine, K, H, increase PCO2
Act on vascular smooth muscles to cause relaxation
Ensures skeletal and coronary muscles get adequate perfusion
What is the effect of increase in mean arterial pressure activating baroreceptors
Reduces sympathetic flow to the heart or increase parasympathetic output
Relaxes blood vessels
Why is the baroreceptor reflex only good for maintaining blood pressure over the short term
Blood pressure sensor can reset to higher levels with persistent increases in blood pressure
What do sympathominetic drugs do
Mimic sympathetic nervous system
α-adrenoceptor agonists, ß-adrenoceptor agonists
Cardiovascular - administration of adrenaline to restore functions in cardiac arrest, anaphylactic shock
ß2-agonist - salbutamol for treatment in asthma
What are examples of adrenoreceptor antagonists
α-adrenoceptor antagonists - antihypertensive agent inhibits noradrenaline action on vascular smooth muscle α1 receptors - vasodilation
ß-adrenoceptor antagonists - propanolol slows heart rate and reduces force of contraction (ß1) but also acts on bronchial smooth muscle (ß2) - bronchoconstriction
Atenolol - selective ß1 - less risk of bronchoconstriction
What are some uses of cholinergics
Muscarinic agonists
Pilocarpine - used in treatment of glaucoma (increased pressure in eyeball) - activates constrictor pupillae muscle
Muscarinic antagonists
Atropine/tropicamide - increase heart rate, bronchial dilation used to dilate pupils for eye examination
