Lab Exam 3

Question 1

What are the two types of myocardial cells?

Answer 1

Conducting (a.k.a. pacemaker or autorhythmic) and contractile cells

Question 2

True or False? Contractile cells are striated?

Answer 2

True

Question 3

What is the characteristic called when cells depolarize and generate an action potential independently?

Answer 3

Autorhythmicity

Question 4

List the steps of the electrical conduction pathway of the heart in order.

Answer 4

SA node, Internodal pathways, AV node, Bundle of His (AV bundle), L & R Bundle branches, Purkinje Fibers

Question 5

What does each step do?

Answer 5

SA node - where the action potential is generated
Internodal pathways - signal spreads through the atria
AV node - the signal slows down to delay the signal until the atria have completed their contraction.
Bundle of His - signal travels down septum. The first step of the electrical conduction pathway located completely in the ventricles.
L & R Bundle branches - the signal continues down the septum between the ventricles
Purkinje Fibers - the signal travels up the walls of the ventricles, and the depolarization wave spreads rapidly through the ventricles and is followed by contraction.

Question 6

What allows an electrical signal to spread from cell to cell in the heart?

Answer 6

Gap junctions

Question 7

What does the P wave represent?

Answer 7

Atrial depolarization. The first point at which the P wave reflects upwards is the electrical activity in the SA node.

Question 8

What does the flat area after the P wave indicate, and what is it called?

Answer 8

It is the PR segment, and it indicates that the signal is not moving very quickly in the AV node.

Question 9

What does the QRS complex represent?

Answer 9

Movement of the depolarization wave through the large mass of the ventricles

Question 10

What does the T wave represent?

Answer 10

Ventricular repolarization

Question 11

What do S-T Segment alterations indicate?

Answer 11

May indicate decreased blood flow to regions of the heart itself - Coronary Ischemia. Or Myocardial Infarction, which is damage or death to heart tissue (a.k.a. heart attack)

Question 12

What do P-R Interval alterations indicate?

Answer 12

Conduction problems in the AV node

Question 13

What do Q-T Interval alterations (elongations) indicate?

Answer 13

It can indicate ion channel defects, low calcium or potassium levels, or drug-related complications.

Question 14

What is the heart rhythm shown in this image?

Answer 14

Sinus arrhythmia

Question 15

What is sinus arrhythmia?

Answer 15

Signal originates at the sinoatrial node, but it is irregular. The length of one cardiac cycle to the next can vary (look at the R-to-R interval).

Question 16

What heart rhythm is show in this image?

Answer 16

Ventricular tachycardia

Question 17

What is ventricular tachycardia?

Answer 17

It is when the signal originates somewhere in the ventricles and the SA node is not able to regain its role as pacemaker.

Question 18

When the electrical signal originates somewhere other than the SA node, the cell that generated the signal are referred to as a(n) ______ _______?

Answer 18

ectopic pacemaker

Question 19

What is the heart rhythm shown in this image?

Answer 19

Premature ventricular contractions (PVC). Note that for one cycle there is no P wave and an inverted T wave.

Question 20

What are premature ventricular contractions?

Answer 20

There is mostly sinus rhythm with an occasional ectopic origin. The person who experiences them typically reports a palpitation or a jump in their heart.

Question 21

What is the condition in this ECG tracing called?

Answer 21

Ventricular Fibrillation

Question 22

What is happening during ventricular fibrillation?

Answer 22

There is no rhythm - sinus nor ectopic. All cells of the heart are depolarizing at their own individual rates - there is no coordination.

A defibrillator must be used to correct this condition by delivering a jolt of electricity causing all of the cells of the heart to depolarize at once. Then the SA nod can take back over as the pacemaker.