Electrical Activity of the Heart

Question 1

Where is the SA node located?

Answer 1

The junction between the superior vena cava and the right atrium

Question 2

What is the speed of conduction from the SA node?

Answer 2

0.05m/s

Question 3

How does electrical activity spread from the right to left atrium?

Answer 3

Bachmann’s bundle at 1.00m/s

Question 4

Where is the AV node located?

Answer 4

The atrioventricular septum

Question 5

Why does the AV node delay?

Answer 5

To allow the atria to empty

Question 6

AV refractoriness

Answer 6

Prevents excess ventricular contraction

Question 7

What are the two types of cardiac action potential?

Answer 7

Nodal and contractile

Question 8

Nodal action potential

Answer 8

Has automaticity and rhythmicity
The If current if hyperpolarisation induced
Can be controlled by innervation, temperature, other pacemakers
1. Ca2+ influx and K+ efflux = pre-potential
2. Depolarisation - threshold is -40 to -50 mV
3. Repolarisation occurs due to K+ efflux

Question 9

How are nodal cells controlled?

Answer 9

Vagal fibres (ACh) - hyperpolarisation and decreased pre-potential
Sympathetic (NE) - increased firing rate
The If current is regulated by cAMP - increased by B1 and B2, decreased by M2
Calcium clock oscillations

Question 10

Cardiac action potential

Answer 10

No automaticity
Effective refractory period
Relative refractory period
Very quick depolarisation with prolonged repolarisation