Cardiac review cards

Question 1

What is the mechanism of Overdrive suppression of pacemaker cells?

Answer 1

Excessive incoming action potentials that are faster than the pacemaker cells normal rate –>

causes a buildup of Na+ ions

this causes increased activity of the Na+/K+ pump, which hyperpolarizes the cell, and makes suppresses its own rate of AP generation.

Question 2

What generates the funny current in the heart pacemaker cells

Answer 2

The HCN4 channel.

Hyperpolarization activated cyclic nucleotide gated channel.

A non-selective positive ion channel, mostly Na+ ions flow through to depolarize the cell.

Question 3

Conduction velocities of:
SA and AV nodes

Purkinje fibers

contractile myocytes

Answer 3

SA and AV nodes:
0.02-0.1 m/s

Purkinje fibers
1-4 m/s

contractile myocytes:
0.1-1 m/s

Question 4

Order of conduction velocities of the different heart tissues, from slowest to fastest:

Answer 4

SA node 0.01 m/s

AV node 0.02-0.05 m/s

Ventricular myocytes 0.3-1.0 m/s

Atrial myocytes 1.0 - 1.2 m/s

Bundle of His 1.2 - 2.0 m/s

Purkinje Cells 2-4 m/s