Session 4-Autonomic Control Of CVS Flashcards
What are the two divisions of the ANS?
Parasympathetic
Sympathetic
What is the enteric nervous system and what is it controlled by?
Network of neurones surrounding GI tract
Controlled via sympathetic and parasympathetic fibres
What does the ANS control in the CVS? (4)
- heart rate
- force of contraction of heart
- peripheral resistance of blood vessels
- amount of venoconstriction
True or false: the ANS initiates electrical activity in the heart
FALSE
What does innervation of the heart control?
Speed and force of contraction
Where do parasympathetic preganglionic fibres synapse with postganglionic cells?
On epicardial surface or within walls of heart at SA and AV node
What do postganglionic cells in the parasympathetic input to the heart release and what does this act on?
ACh
Acts on M2-receptors
What effect does activating M2 receptors have on the heart? (2)
Decrease heart rate (-ve chronotropic effect)
Decrease AV node conduction velocity
What does the sympathetic trunk innervate and what does it release?
SA node
AV node
Myocardium
Releases noradrenaline
What does the sympathetic trunk act on?
Beta1-adrenoceptors
What effect does activating beta1-adrenoceptors have on the heart? (2)
1) increases heart rate (positive chronotropic effect)
2) increases force of contraction (positive inotropic effect)
True or false: beta2 and beta3 adrenoceptors are also present in the heart but the main effect is mediated by beta1 receptors
TRUE
What do baroreceptors detect?
Pressure changes
Where is the cardiovascular control centre located?
Medulla oblongata
What is the term given to the SA node setting the rhythm of the heart?
Sinus rhythm
How does sympathetic activity affect the pacemaker potential?
Increases slope in membrane potential/time graph so AP are fired closer together and the heart rate therefore increases
How does parasympathetic activity affect the pacemaker potential?
Decreases slope of membrane potential/time graph, action potential fires slower so heart rate decreases
Complete the sentences:
Sympathetic effect on pacemaker potentials is mediated by _______ receptors. Stimulation of G alpha-s ____________ cAMP which _________ ____ pacemaker potential.
Beta1
Increases
Speeds up
Complete the sentences:
Parasympathetic effect is mediated by __ receptors. G alpha-_ increases __ conductance and __________ cAMP.
M2
i
K+
Decreases
How does noradrenaline increase force of contraction?
Acts on beta1 receptors in myocardium, causing an increase in cAMP and this activates PKA:
- phosphorylation of Ca2+ channels increases Ca2+ entry during plateau of AP
- increased uptake of Ca2+ in SR
- increased sensitivity of contractile machinery to Ca2+
True or false: most vessels receive parasympathetic innervation
FALSE - sympathetic
Give an example of tissue that has parasympathetic innervation
Erectile tissue
Which receptors do most arteries and veins have?
Alpha1-adrenoreceptors
What allows for vasodilation to occur?
Vasomotor tone
Which blood vessels have beta2-adrenoceptors as well as alpha1-adrenoceptors? (3)
Skeletal muscle
Myocardium
Liver
Which adrenoceptor does circulating adrenaline have a higher affinity for?
Beta2
True or false: at higher concentrations, circulating adrenaline will also activate alpha1 receptors
TRUE
What does the activation of beta2 adrenoceptors cause in vascular smooth muscle?
Vasodilation
How does the activation of beta2-adrenoceptors cause vasodilation?
Increases cAMP -> PKA -> opens K+ channels and inhibits MLCK -> relaxation of smooth muscle
What does the activation of alpha1-adrenoceptors cause?
Vasoconstriction
How does the activation of alpha1-adrenoceptors cause vasoconstriction?
Stimulates IP3 production -> increase in intracellular Ca2+ from stores and via influx of extracellular Ca2+ -> contraction of smooth muscle
True or false: active tissue produces fewer metabolites such as adenosine, K+, H+
FALSE - produces more metabolites
What effect does a local increase in metabolites have?
Strong vasodilator effect
Complete the sentence:
Metabolites are more important for ensuring adequate _________ of skeletal and coronary muscle than activation of ____-receptors
Perfusion
Beta2
How are changes in the state of the cardiovascular system communicated to the brain?
Via afferent nerves
Which receptors detect arterial pressure and are said to be on the “high pressure side of the system”?
Baroreceptors
Which receptors detect venous pressure and are said to be on the “low pressure side of the system”?
Atrial receptors
Where are baroreceptors located? (2)
Carotid sinus
Aortic arch
What are nerve endings in the carotid sinus and aortic arch sensitive to?
Stretching
What does increased arterial pressure do to baroreceptors?
Stretches the receptors
Where do nerves on the aortic arch go to?
Vagus nerve
What does the baroreceptor reflex do?
Maintains blood pressure, especially when posture changes
What counteracts increased mean arterial pressure in the baroreceptor reflex?
Bradycardia
Vasodilation
What do sympathomimetics do?
Mimic the sympathetic nervous system
What do sympathomimetics do in the cardiovascular system? (3)
1) administer adrenaline to restore function in cardiac arrest
2) beta1-agonist - dobutamine given in cardiogenic shock
3) adrenaline administered for anaphylactic shock
Which sympathomimetic is used to treat asthma?
Beta2-agonist - salbutamol
Give an example of an alpha-adrenoceptor antagonist and give its use
Alpha1 antagonist eg prazosin
Anti-hypertensive agent - inhibits noradrenaline action on vascular smooth muscle alpha1-receptors (causes vasodilation)
Is prazosin used often as an anti-hypertensive agent?
No-there are better things to use
Give an example of a non-selective beta-adrenoceptor antagonist and its use
Propranolol
Non-selective beta1/beta2 antagonist, slows heart rate and reduces force of contraction (beta1) but also acts on bronchial smooth muscle (beta2) to cause bronchoconstriction
Give an example of a selective beta1 antagonist
Atenolol
Give an example of a muscarinic agonist and give its use
Pilocarpine
Treatment of glaucoma - activates constrictor pupillae muscle
Give an example of a muscarinic antagonist and give its use
Atropine or tropicamide
Increases heart rate, bronchial dilation
Used to dilate pupils for examination of eye
