Flashcards in CVS Session 4 (Lecture 4.2) Deck (37):
Normally which nerve controls the heart rate?
What does the ANS regulate?
1) HR, BP, body temp etc... (homeostasis)
2) Co-ordinate body's response to exercise and stress
3) Outside voluntary control
What are the two divisions of the ANS?
Sympathetic and parasympathetic
Describe the organisation of the sympathetic division.
1) Thoracolumbar outflow
2) Preganglionic neurones arise from T1 to L2/3
3) Most synapse with postganglionic neurones in the paravertebral chain of ganglia
4) Some synapse in a number of prevertebral ganglia.
Which neurones in the sympathetic ANS synapse in prevertebral ganglia?
Coeliac, superior and inferior mesenteric
Describe the organisation of the parasympathetic division.
1) Craniosacral outflow
2) Preganglionic fibres travel in CNs (III, VII, IX and X) or sacral outflow from S2-S4
3) Synapse with neurones in ganglia close to the target tissue
4) Short postganglionic neurones
What is released by preganglionic neurones and which receptor do they act on?
Acetylcholine is released and acts on nicotinic Ach Rs.
What do nAChRs have?
Ion channel allowing an influx of Na+ and efflux of K+. This causes depolarisation of the postganglionic membrane
What neurotransmitters are released by postganglionic sympathetic and parasympathetic fibres? Which receptors do they act on?
1) Sympathetic - Noradrenaline (usually) acting on adrenoceptors
2) Parasympathetic - ACh acting on muscarinic receptors.
What is the exception of the sympathetic innervation?
Sweat glands which receive ACh acting on mAChRs.
What are adrenoceptors and mAChRs?
What occurs at chromaffin cells to stimulate release of adrenaline?
Acetylcholine is released to act on chromaffin cell in the adrenal medulla to release adrenaline into the adrenaline.
In reference to the heart and vascular system, what and how does the parasympathetic division do?
1) Vagus nerve (X)
2) Synapse with postganglionic cells on epicardial surface or within walls of heart at SAN and AVN
3) Postganglionic release Ach
4) Acts on M2 receptors causing a) decrease HR (chonotropic effect) and decrease in AVN cnduction velocity.
In reference to the heart and vascular system, what and how does the sympathetic division do?
1) Postganglionic fibres from the sympathetic trunk (cardiac accelerator)
2) Innervate SAN, AVN and ventricular myocardium
3) Release NA
4) Act on B1 receptors to increase HR and increase FOC
Describe the effect on the SAN firing by the sympathetic division.
Sympathetic activity increases depolarising slope to increase firing.
1) Increase in cytosolic cAMP via Gas GPCRs.
Describe the effect on the SAN firing by the parasympathetic division.
Parasympathetic activity decreases time to depolarise to decrease firing rate
1) Increase K+ conductance and decrease cAMP
How does NA increase the FOC?
1) NA acts on B1 receptors in myocardium causes an increase in cAMP which activates PKA
2) PKA phosphorylates the cytosolic portion of Ca2+ channels increasing Ca2+ entry during AP
3) Increased uptake of Ca2+ in SR leading to more release
4) Increased sensitivity of contractile machinery to Ca2+
Most vessels are innervated by which branch of the ANS?
What is the exception in vessel innervation?
Erectile tissue have parasympathetic innervation
Which type of adrenoceptor do most arteries and veins have?
Which additional adrenoceptor do coronary,skeletal muscle and liver blood vessels have?
What adrenoceptor will circulating adrenaline act on vascular cells? What would be the subsequent result?
Beta 2 causing vasodilatation
What would be the effect of giving adrenaline at a pharmacological dose to the vasomotor tone?
Activates alpha 1 receptors causing vasoconstriction
How does activating B2 receptors cause vasodilation?
Increase in cAMP, PKA, opens K+ channels + inhibits MLCK causing relaxation of SMCs
How does activating alpha 1 receptors cause vasoconstriction?
Stimulates IP3 production releasing Ca2+ from SR causing contraction via MLCK.
What are the role of local active metabolites? Give examples of metabolites.
Strong vasodilator effect e.g. adenosine, K+, H+, increase pCO2
Important for ensuring adequate perfusion of skeletal and coronary muscle.
Where are baroreceptors located?
Carotid sinus and aortic arch
In the carotid sinus, which nerve carries firing APs towards the medulla?
Describe the baroreceptor reflex?
1) Mean arterial pressure increases
2) Stretches wall of arteries causing baroreceptors to increase firing towards the medulla
3) Medulla receives signals and sends signals to slow the HR and vasodilate vessels via efferent pathways
4) Bradycardia and vasodilation cause decreased MAP.
What type of control is the baroreceptor reflex?
What does dobutamine act on and do?
B1 agonist - given in cardiogenic shock to boost HR
What does salbutamol act on and do?
B2 agonist - treatment for asthma
What does prazosin act on and do?
A1 antagonist - anti hypertensive agent by inhibiting NA on VSMCs
What does propranolol act on and do?
Non selec B1/B2 antagonist - slows HR, reduces FOC but causes bronchoconstriction
What does atenolol act on and do?
Selec B1 antagonist - slows HR and FOC
What does pilocarpine act on and do?
Muscarinic agonist - treatment of glaucoma by activating constrictor pupillae muscle (decreases intraocular pressure via opening of canal of schlemm)