Phase 4 of SA nodal action potentials is generated in part by

increased inward movement of calcium ions

Conduction velocity in non-nodal cardiac cells is decreased by

decreasing the slope of phase 0

Normal rhythm of the heart originates from

cells within the sinoatrial node

The initial depolarization during a cardiac action potential results from

opening of fast sodium channels

The conduction velocity of AV nodal action potentials is increased by

stimulation of sympathetic adrenergic nerves

10. Which of the following is INCORRECT concerning cardiac muscle?

It has less mitchondria than skeletal muscle

The firing rate of SA nodal pacemaker action potentials is decreased by

vagus nerve activation which decreases the slope of phase 4

Resting heart rate is slower than the intrinsic firing rate of the SA node because

vagal tone decreases the slope of phase 4

Phase 3 of non-pacemaker action potentials results primarily from

increased potassium conductance

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cardiac electrophysiology

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Questions 13

Answers

1
The region of the heart with the slowest conduction velocity is the
atrial muscle
ventricular Purkinje fibers
Bundle of His
atrioventricular node
2
Phase 4 of SA nodal action potentials is generated in part by
increased activity of the Na+/K+-ATPase pump
“funny” currents produced by inward movement of Na+ ions
increased inward movement of calcium ions
opening of potassium channels
3
Conduction velocity in non-nodal cardiac cells is decreased by
activation of fast sodium channels
sympathetic nerve activation
decreasing the slope of phase 0
4
Normal rhythm of the heart originates from
ectopic pacemakers
sympathetic nerve activity
cells within the sinoatrial node
cells within the atrioventricular node
5
SA node destruction will result in
increased heart rate
decreased heart rate
Cardiac arrest
Heart attack
6
The duration of the effective refractory period in cardiac cells can by increased by
shortening phase 2
shortening phase 3
opening L-type calcium channels
inhibiting potassium channels
7
The ion having the highest intracellular concentration in a resting cardiac cell is
calcium
sodium
potassium
8
The initial depolarization during a cardiac action potential results from
a large increase in intracellular sodium concentration
opening of fast sodium channels
an increase in the relative conductance of potassium
a large decrease in intracellular potassium concentration
9
The conduction velocity of AV nodal action potentials is increased by
cellular hypoxia
stimulation of sympathetic adrenergic nerves
decreasing the slope of phase 4 of the AV nodal cells
drugs that activate the vagus nerves to the heart
10
10. Which of the following is INCORRECT concerning cardiac muscle?
Cardiac cells are smaller than skeletal muscle cells.
It has less mitchondria than skeletal muscle
Heart cells communicate via gap junctions
Cardiac cells are attached by intercalated disc.
11
The firing rate of SA nodal pacemaker action potentials is decreased by
hyperthyroidism
increased circulating concentrations of epinephrine
vagus nerve activation which decreases the slope of phase 4
hypokalemia which increases the slope of phase 4
12
Resting heart rate is slower than the intrinsic firing rate of the SA node because
vagal tone decreases the slope of phase 4
High 3xtracellular K+ concentration in SA nodal cells
sympathetic tone suppresses “funny” currents
sympathetic tone suppresses inward calcium movement
13
Phase 3 of non-pacemaker action potentials results primarily from
inactivation of fast sodium channels
decreased activity of the Na+/K+-ATPase pump
increased calcium influx through L-type channels
increased potassium conductance

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