Electrical activity of the heart

Question 1

How big is the SAN?

Answer 1

15mmx5mmx2mm

Question 2

How big is the AVN?

Answer 2

22mmx10mmx3mm

Question 3

AV delay

Answer 3

Allows atria to expel blood, sow conduction through AN-N = 0.05m/s

Question 4

AV refractoriness

Answer 4

Prevents excess ventricular contraction. Time period before another AP can fire.

Question 5

Conduction speed of the Bundle of His

Answer 5

1m/s

Question 6

Conduction speed of the Purkinje fibres

Answer 6

4m/s

Question 7

What is the resting potential of atrial and ventricular muscle?

Answer 7

-80mV

Question 8

How long is a myocardial AP compared to a nerve AP?

Answer 8

200ms compared to 1-2ms

Question 9

How does parasympathetic nervous system control pacemakers?

Answer 9

Vagal fibres (Ach) cause hyperpolarisation and decrease pre potential slope by blocking If

Question 10

How sympathetic nervous system control pacemakers?

Answer 10

NA, causes increase in pre potential slope so increases firing, If channels increase activity by activating B1 and B2 or decreasing M2 receptors which regulate cAMP

Question 11

Effective refractory period

Answer 11

Period where another AP won’t fire due to Sodium channels being inactive in cardiac muscle cells

Question 12

What sodium and calcium channel is initiated in cardiac myocytes?

Answer 12

Nav1.5. L-type calcium channels

Question 13

What is the maximum diastolic potential

Answer 13

Lowest point on the graph for pacemaker cells