Autonomic Control Of The CVS

Question 1

Sympathetic and parasympathetic effect and receptors: pupil of the eye

Answer 1

Dilation a1

Contraction M3

Question 2

Sympathetic and parasympathetic effect and receptors: airways of lungs

Answer 2

Relax B2

Contract M3

Question 3

Sympathetic and parasympathetic effect and receptors: heart

Answer 3

Increase rate and force of contraction B1

Decrease rate M2

Question 4

Sympathetic and parasympathetic effect and receptors: sweat glands

Answer 4

Localised secretion a1
Generalised secretion M3
No effect for parasympathetic

Question 5

The ANS controls…

Answer 5

Heart rate, force of contraction of heart, peripheral resistance of blood vessels, amount of venoconstriction

Question 6

Where does the parasympathetic input to the heart arise from?

Answer 6

10th (X) cranial nerve

Vagus

Question 7

Where does the parasympathetic input to the heart synapse?

Answer 7

Postganglionic cells on epicardial surface or within walls of heart at SA and AV node

Question 8

What do postganglionic cells release and which receptors do they act on? What is the effect on the heart?

Answer 8

ACh
M2
- decrease heart rate (-ve chronotropic effect)
- decrease AV node conduction velocity

Question 9

Which part of the heart do the sympathetic fibres innervate and what do they release? Which receptors?

Answer 9

SA node, AV node and myocardium
Release noradrenaline
B1 adrenoceptors

Question 10

What effect does the sympathetic nervous system have on the heart?

Answer 10

Increases heart rate (+ve chrontropic effect)

Increases force of contraction (+ve inotropic effect)

Question 11

Where are the baroreceptors located in the heart?

Answer 11

Carotid sinus

Arch of aorta

Question 12

How does noradrenaline increase force of contraction?

Answer 12

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+

Question 13

Which receptors do most arteries and veins have?

Answer 13

Alpha1 adrenoceptors

Coronary and skeletal muscle vasculature also have β2 receptors

Question 14

Which receptors do adrenaline and noradrenaline bind to?

Answer 14

Adrenaline has a higher affinity for B2 adrenoceptors, but will also bind to a1 adrenoceptors at higher concentrations

Question 15

Activating β2 adrenoreceptors

Answer 15

Causes vasodilation

Increases cAMP -> PKA -> opens potassium channels + inhibits MLCK -> relaxation of smooth muscle

Question 16

Activating a1 adrenoceptors

Answer 16

Causes vasoconstriction
Stimulates IP3 production
Increase in [Ca2+]in from stores and via influx of extracellular Ca2+ -> contraction of smooth muscle

Question 17

Baroreceptors

Answer 17

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.

Question 18

Clinical application: drugs acting on the ANS

Answer 18

Sympathomimetics
Adrenoceptor antagonists
Cholinergics

Question 19

Sympathomimetics

Answer 19

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

Question 20

Adrenoreceptor antagonists

Answer 20

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

Question 21

Cholinergics

Answer 21

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