CVS - Autonomic Nervous System

Question 1

What areas of the body does the ANS control?

Answer 1

• smooth muscle (vascular and visceral)
• exocrine secretion
• rate and force of contraction of the heart

Question 2

What are the two divisions of the ANS?

Answer 2

• parasympathetic nervous system (cranio-sacral origin)

- sympathetic nervous system (thoraco-lumbar origin)

Question 3

Which receptors does the sympathetic nervous system use to increase the rate of contraction in the heart?

Answer 3

Beta-1

Question 4

Which receptors does the para-sympathetic nervous system use to decrease the heart rate?

Answer 4

Muscarinic (m2)

Question 5

Which receptors does the sympathetic nervous system use to relax the lungs?

Answer 5

Beta-2

Question 6

What does the ANS control within the cardiovascular system?

Answer 6

• heart rate
• force of contraction
• peripheral resistance of blood vessels
• amount of venoconstriction
• DOES NOT initiate electrical activity in the heart, if heart is denervated will beat extremely quickly

Question 7

Where does the parasympathetic input enter the heart?

Answer 7

It synapses with postganglionic cells on the epicardial surface or within walls at SA and AV node

Question 8

Which neurotransmitter and receptor does the parasympathetic nervous system use in the heart?

Answer 8

Acetylcholine, which acts on m2 receptors

Question 9

Describe the sympathetic input to the heart

Answer 9

• postganglionic fibres from sympathetic trunk innervate SA and AV node and myocardium
• release noradrenaline
• acts on beta-1 adrenoreceptors
• increases heart rate and force of contraction

Question 10

Where are baroreceptors found in the heart?

Answer 10

In the arch of the aorta and in the carotid sinus

Question 11

What effect does the sympathetic nervous system have on the slope of the pacemaker potential?

Answer 11

It increases it, meaning there is less time between action potentials so the heart rate speeds up.

Question 12

What effect does the parasympathetic nervous system have on the pacemaker potential?

Answer 12

It decreases the slope, meaning that there is more time between action potentials and the heart rate slows

Question 13

How does noradrenaline increase the force of contraction in the heart?

Answer 13

• it acts on beta-1 receptors in myocardium which causes an increase in cAMP
• this activates PKA
• phosphorylation of Ca2+ channels increases Ca2+ entry during plateau of the action potential
• increased uptake of Ca2+ in SR
• increased sensitivity of contractile machinery to Ca2+

Question 14

True or false - most vessels have sympathetic innervation and alpha-1 adrenoceptors

Answer 14

True

Question 15

Some blood vessels have beta-2 receptors as well as alpha-1 receptors. Which would circulating adrenaline bind to more preferentially?

Answer 15

Noradrenaline from the SNS would bind to alpha-1, and circulating adrenaline would bind to beta-2

Question 16

How does activating beta-2 adrenoceptors cause vasodilation?

Answer 16

Increases cAMP, increases PKA, opens potassium channels and inhibits MLCK which leads to relaxation of smooth muscle

Question 17

How does activating alpha-1 adrenoceptors cause vasoconstriction?

Answer 17

Stimulates IP3 production, causing an increase in interior [Ca2+] from stores and via influx from outside cell. This leads to contraction of smooth muscle.

Question 18

What is the role of metabolites in vasodilation?

Answer 18

Active tissue produces more metabolites, eg. H+ which leads to a vasodilator effect in the local area of the increase. This allows adequate perfusion of muscles

Question 19

Which receptors detect low blood pressure?

Answer 19

Atrial receptors - baroreceptors detect high blood pressure

Question 20

What happens if raised arterial pressure activates the baroreceptors in the aorta?

Answer 20

Impulse travels via the afferent pathway to the coordinating centre. Impulse travels via efferent pathways to the effectors. Bradycardia and vasodilation counteract the increased mean arterial pressure

Question 21

Give a weakness of baroreceptors

Answer 21

They can reset to higher levels with persistent increases in blood pressure

Question 22

Give some samples of cardiovascular uses of sympathomimetics

Answer 22

• administration of adrenaline to restore function in cardiac arrest
• dobutamine (b1 agonist) can be given in cardiogenic shock
• adrenaline given for anaphylactic shock

Question 23

Give an example of a use of alpha-adrenoceptor antagonists

Answer 23

Can be used as an anti-hypertensive agent

Question 24

Give an example of a beta-adrenoreceptor antagonist

Answer 24

• propranolol can be used to slow heart rate and reduce force of contraction, but also causes bronchoconstriction

Question 25

Give an example of a use of a muscarinic agonist

Answer 25

Pilocarpine is used in treatment of glaucoma, activates constrictor pupillae muscle

Question 26

Give an example of a muscarinic antagonist

Answer 26

Atropine increases heart rate and bronchial dilation, used to dilate pupils for examination of the eye