Physiology

Question 1

Where is the SA node located?

Answer 1

The upper right atrium

Near where the SVC enters the right atrium

Question 2

Do the cells in the SA node have a stable resting membrane potential?

Answer 2

No

Question 3

What is spontaneous pacemaker potential?

Answer 3

Where membrane potential is taken to a threshold to generate an action potential in the SA nodal cells

Question 4

What causes the pacemaker potential?

Answer 4

Decrease in K+ efflux

Slow Na+ influx (the funny current)

Question 5

What causes the rising phase of the action potential?

Answer 5

Depolarisation caused by activation of voltage gater Ca2+ channels
(CALCIUM INFLUX)

Question 6

What causes the falling phase of the action potential?

Answer 6

Depolarisation caused by activation of K+ channels

K+ EFFLUX

Question 7

How does excitation spread through the heart

Answer 7

SA node 
Cell-to-cell conduction 
AV node 
Bundle of His 
Left & right branches 
Purkinje fibres

Question 8

How does excitation spread from SA node to AV node?

Answer 8

Via gap junctions

Question 9

Why is conduction delayed in the AV node?

Answer 9

Allows atrial systole (contraction) to precede ventricular systole

Question 10

What causes phase 0 of the ventricular muscle action potential?

Answer 10

Fast Na+ influx

Question 11

What causes phase 1 of the ventricular muscle action potential?

Answer 11

Closure of Na+ channels and transient K+ efflux

Question 12

What causes phase 2 (plateau phase) of the ventricular muscle action potential?

Answer 12

Mainly Ca2+ influx

Question 13

What causes phase 3 of the ventricular muscle action potential?

Answer 13

Closure of Ca2+ channels and K+ efflux

Question 14

What is phase 4 of the ventricular muscle action potential?

Answer 14

Resting membrane potential

Question 15

Which nervous system mainly influences heart rate?

Answer 15

Autonomic Nervous System

Question 16

What does sympathetic stimulation do to heart rate?

Answer 16

Increases heart rate

Question 17

What does parasympathetic stimulation do too heart rate?

Answer 17

Decreases the heart rate

Question 18

What is the parasympathetic supply to the heart?

Answer 18

Vagus nerve

Question 19

What is a normal resting heart rate?

Answer 19

60 - 100 bpm

Question 20

What does vagal stimulation do to the heart?

Answer 20

Slows heart rate and increases AV node delay

Question 21

What neurotransmitter is involved in parasympathetic stimulation of the heart?

Answer 21

Acetyl choline acting through M2 receptor

Question 22

How does atropine act on the heart?

Answer 22

Competitive inhibitor of Acetyl choline - used in extreme bradycardia to speed up the heart

Question 23

What is the effect of vagal stimulation on pacemaker potentials?

Answer 23

Slope of pacemaker potentials DECREASES

Question 24

What is the sympathetic supply to the heart?

Answer 24

Cardiac sympathetic nerves supply the SA and AV node and the myocardium

Question 25

What does sympathetic stimulation do to the heart?

Answer 25

Increases heart rate Decreases AV node delay Increases force of contraction

Question 26

What is the neurotransmitter for sympathetic stimulation of the heart?

Answer 26

Noradrenaline acting through B1 adrenoceptors

Question 27

What effect does noradrenaline have on pacemaker cells?

Answer 27

Slope of pacemaker potential INCREASES

Question 28

Where does the excitation of the heart originate?

Answer 28

Pacemaker cells in the SA node