CVS Session 4 (Lecture 4.2)

Question 1

Normally which nerve controls the heart rate?

Answer 1

Vagus nerve

Question 2

What does the ANS regulate?

Answer 2

1) HR, BP, body temp etc… (homeostasis)
2) Co-ordinate body’s response to exercise and stress
3) Outside voluntary control

Question 3

What are the two divisions of the ANS?

Answer 3

Sympathetic and parasympathetic

Question 4

Describe the organisation of the sympathetic division.

Answer 4

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.

Question 5

Which neurones in the sympathetic ANS synapse in prevertebral ganglia?

Answer 5

Coeliac, superior and inferior mesenteric

Question 6

Describe the organisation of the parasympathetic division.

Answer 6

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

Question 7

What is released by preganglionic neurones and which receptor do they act on?

Answer 7

Acetylcholine is released and acts on nicotinic Ach Rs.

Question 8

What do nAChRs have?

Answer 8

Ion channel allowing an influx of Na+ and efflux of K+. This causes depolarisation of the postganglionic membrane

Question 9

What neurotransmitters are released by postganglionic sympathetic and parasympathetic fibres? Which receptors do they act on?

Answer 9

1) Sympathetic - Noradrenaline (usually) acting on adrenoceptors
2) Parasympathetic - ACh acting on muscarinic receptors.

Question 10

What is the exception of the sympathetic innervation?

Answer 10

Sweat glands which receive ACh acting on mAChRs.

Question 11

What are adrenoceptors and mAChRs?

Answer 11

GPCRs

Question 12

What occurs at chromaffin cells to stimulate release of adrenaline?

Answer 12

Acetylcholine is released to act on chromaffin cell in the adrenal medulla to release adrenaline into the adrenaline.

Question 13

In reference to the heart and vascular system, what and how does the parasympathetic division do?

Answer 13

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.

Question 14

In reference to the heart and vascular system, what and how does the sympathetic division do?

Answer 14

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

Question 15

Describe the effect on the SAN firing by the sympathetic division.

Answer 15

Sympathetic activity increases depolarising slope to increase firing.

1) Increase in cytosolic cAMP via Gas GPCRs.

Question 16

Describe the effect on the SAN firing by the parasympathetic division.

Answer 16

Parasympathetic activity decreases time to depolarise to decrease firing rate

1) Increase K+ conductance and decrease cAMP

Question 17

How does NA increase the FOC?

Answer 17

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+

Question 18

Most vessels are innervated by which branch of the ANS?

Answer 18

Sympathetic innervation

Question 19

What is the exception in vessel innervation?

Answer 19

Erectile tissue have parasympathetic innervation

Question 20

Which type of adrenoceptor do most arteries and veins have?

Answer 20

Alpha 1

Question 21

Which additional adrenoceptor do coronary,skeletal muscle and liver blood vessels have?

Answer 21

Beta 2

Question 22

What adrenoceptor will circulating adrenaline act on vascular cells? What would be the subsequent result?

Answer 22

Beta 2 causing vasodilatation

Question 23

What would be the effect of giving adrenaline at a pharmacological dose to the vasomotor tone?

Answer 23

Activates alpha 1 receptors causing vasoconstriction

Question 24

How does activating B2 receptors cause vasodilation?

Answer 24

Increase in cAMP, PKA, opens K+ channels + inhibits MLCK causing relaxation of SMCs

Question 25

How does activating alpha 1 receptors cause vasoconstriction?

Answer 25

Stimulates IP3 production releasing Ca2+ from SR causing contraction via MLCK.

Question 26

What are the role of local active metabolites? Give examples of metabolites.

Answer 26

Strong vasodilator effect e.g. adenosine, K+, H+, increase pCO2

Important for ensuring adequate perfusion of skeletal and coronary muscle.

Question 27

Where are baroreceptors located?

Answer 27

Carotid sinus and aortic arch

Question 28

In the carotid sinus, which nerve carries firing APs towards the medulla?

Answer 28

Glossopharyngeal

Question 29

Describe the baroreceptor reflex?

Answer 29

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.

Question 30

What type of control is the baroreceptor reflex?

Answer 30

Short term

Question 31

What does dobutamine act on and do?

Answer 31

B1 agonist - given in cardiogenic shock to boost HR

Question 32

What does salbutamol act on and do?

Answer 32

B2 agonist - treatment for asthma

Question 33

What does prazosin act on and do?

Answer 33

A1 antagonist - anti hypertensive agent by inhibiting NA on VSMCs

Question 34

What does propranolol act on and do?

Answer 34

Non selec B1/B2 antagonist - slows HR, reduces FOC but causes bronchoconstriction

Question 35

What does atenolol act on and do?

Answer 35

Selec B1 antagonist - slows HR and FOC

Question 36

What does pilocarpine act on and do?

Answer 36

Muscarinic agonist - treatment of glaucoma by activating constrictor pupillae muscle (decreases intraocular pressure via opening of canal of schlemm)

Question 37

What does atropine or tropicamide act on and do?

Answer 37

Muscarinic antagonist - increases HR, bronchial dilation and dilation of eye for fundoscopy.