Lecture 22: Electrical Conductance

Question 1

Contraction of cardiac muscle cells to bring about the ejection of blood is triggered by

Answer 1

Action potentials sweeping across the muscle membranes

Question 2

Autorhythmicity

Answer 2

Ability to generate action potentials, allowing the heart to contract

Question 3

Various autorhythmic cells have different rates of _____ to threshold, thus

Answer 3

• depolarization

- rates at which they are normally capable of generating action potential also differ

Question 4

What is the native pacemaker of the heart

Answer 4

SA node

Question 5

What exhibits the fastest rate of autorhythmicity

Answer 5

SA node

Question 6

Overdrive suppression

Answer 6

The SA node directly suppresses the autorhythmicity of other autorhythmic cells.

They are activated by action potentials originating in the SA node before they are able to reach threshold at their own slower rate

Question 7

Escape beat

Answer 7

If the SA node becomes nonfunctional, the AV node assumes pacemaker activity (latent pacemakers)

Question 8

Once initiated in the SA node, the action potential

Answer 8

spreads throughout the rest of the heart

Question 9

For efficient cardiac function, the spread of excitation should satisfy three criteria:

Answer 9

1. Atrial excitation and contraction should be complete before the onset of ventricular contraction.
2. Excitation of cardiac muscle fibers should be coordinated to ensure that each heart chamber contracts as a unit to accomplish efficient heart pumping.
3. The pair of atria and pair of ventricles should be functionally coordinated so that both members of the pair contract simultaneously which permits the synchronized pumping of blood into the pulmonary and systemic circulation.

Question 10

Complete ventricular filling requires that atrial contraction precedes

Answer 10

ventricle contraction

Question 11

Fibrillation

Answer 11

Random uncoordinated excitation and contraction of cardiac cells

Question 12

Why does ventricular fibrillation cause death

Answer 12

because heart rate is not able to pump blood into the arteries

Question 13

How does the action potential from the SA node spread through both atria?

Answer 13

From cell to cell via gap junctions

Question 14

Interatrial pathway

Answer 14

• Extends from the SA node in the right atrium to the left atrium
• Transmission impulses very rapidly from SA node to the left atrium to the left atrium.
• Ensures that both atria become depolarized to contract simultaneously

Question 15

Internodal pathway

Answer 15

• Extends from the SA to AV node
• Nonconductive fibrous tissue
• Directs spread of action potential originating at the SA node to AV node to ensure sequential contraction of the ventricles following atrial contraction

Question 16

AV Nodal Delay

Answer 16

• Action potential is conductive relatively slowly through the AV node
• Slowness enables the atria to become completely depolarized and to contract, emptying their contents into the ventricles before ventricular depolarization and contraction occur
• AV nodal delay allows time for complete ventricular filling

Question 17

Following AV nodal delay

Answer 17

the impulse travels rapidly down the bundle of his and throughout the ventricular myocardium via the purkenje fibers

Question 18

Does the cardiac action potential terminate on every cell?

Answer 18

Nope

Question 19

Ventricular excitation

Answer 19

Rapid ventricular contraction via the ventricular conduction system ensures that the ventricles contract as a unit.
Coordinated contraction enables them to efficiently eject blood into both the systemic and pulmonary circulation at the same time