Electrophysiology

Question 1

what is the order of the pacemaker cells of the heart?

Answer 1

SA – AV – bundle of His – left and right branches – purkinje fibers

Question 2

what is the primary pacemaker of the cell and where is it located?

Answer 2

SA - posterior wall upper right atrium

Question 3

what is the purpose of slower conduction through the AV node?

Answer 3

allows for the atria to empty

Question 4

what is the order of depolarization of nodal cells in the heart?

Answer 4

1. Funny (HCN) channels – Na+ in
2. T-type channels – Ca2+ in until threshold
3. L-type channels – Ca2+ in until 0
4. depolarization with K+ rushing out

Question 5

how is cardiac muscle contraction different from skeletal muscle contraction?

Answer 5

cardiac muscle is a single contraction with a longer refractory period

Question 6

why is there a long refractory period in heart muscle contraction?

Answer 6

keeps all activated muscle fibers contracted for a set period of time
–muscle has to completely relax before it can fire again

Question 7

what is the role of calcium in heart muscle contraction?

Answer 7

calcium allows the cell to remain depolarized for a longer period of time

Question 8

what would happen if you block Ca2+ channels in the heart?

Answer 8

longer plateau phase, which would slow down HR

Question 9

what happens to the heart rate during sympathetic response?

Answer 9

increases BP and speeds up the heart

Question 10

what happens to the heart during parasympathetic response?

Answer 10

slows down the heart

Question 11

what are chronotropic effects of the heart? positive and negative?

Answer 11

effects cardiac pace
positive – faster rate
negative – slower rate (Ca2+ blockers)

Question 12

what are ionotropic effects of the heart? positive and negative?

Answer 12

force of contraction
positive – increases contraction
negative – decreases contraction