L6 Heart- Cardiac Conduction

Question 1

Describe the structure of intercalated disc.

Answer 1

Specialized region of intercellular connections between cardiac cells with 3 types of adhering jxns:

1. Fascia adherens- actin anchoring sites
2. Macula adherens (desmosomes)- binds intermediate filaments
3. Gap junctions- connections that allow current to conduct between cardiac cells

Question 2

Describe the function of intercalated disc and the role of gap jxns in cardiac conduction.

Answer 2

Connect cardiac cells together mechanically and electrically

• Gap jxns couple cells together for conduction
• Gap jxns are sensitive to intracellular Ca and pH

Question 3

Describe the structure-fxn relationship of SA node and AV node

Answer 3

Fxn: pacemaker activity
Few gap jxn connections= slow conduction
Few myofibrils= weak contraction

Question 4

Explain how the space constant and AP upstroke determine electrical conduction between cardiac cells.

Answer 4

1

Question 5

Define the relationship between resting Vm and the Na channel availability.

Answer 5

More negative Vm= more Na channel availability

Question 6

How does the relationship between resting Em and Na channel availability affect conduction in the heart.

Answer 6

As the Vm becomes more positive (depolarizes), less Na channels are available and the fast response AP upstroke decreases and conduction slows.

Question 7

Define the PR interval.

Answer 7

1

Question 8

Define the QRS complex.

Answer 8

1

Question 9

How can the PR interval and QRS complex be used to evaluate conduction through the AV node?

Answer 9

1

Question 10

How can the PR interval and QRS complex be used to evaluate conduction through the ventricular muscle?

Answer 10

1

Question 11

Explain the cellular mechanisms by which PS (ACh) activity affects conduction through AV node.

Answer 11

1

Question 12

Explain the cellular mechanisms by which Symp (NE) nerve activity affects conduction through the AV node.

Answer 12

1

Question 13

Explain how autonomically- induced changes in AV conduction manifest on EKG.

Answer 13

1

Question 14

Define 1st, 2nd and 3rd degree AV block.

Answer 14

1

Question 15

Define supraventricular tachycardia

Answer 15

1

Question 16

Define ventricular tachycardia

Answer 16

1

Question 17

Define atrial fibrillation

Answer 17

1

Question 18

Define ventricular fibrillation

Answer 18

1

Question 19

Compare SVT, VT, AFib, VT’s effects on cardiac fxn/output.

Answer 19

1

Question 20

What is healing over?

Answer 20

Increase in internal resistance due to a decrease in number of open gap jxns, caused by increase in intracellular Ca and H ions (decrease pH).
-Cells close gap jxns and disconnect dead from living cells

Question 21

Describe the structure-fxn relationship of atrial and ventricular muscle.

Answer 21

Fxn: conduction/contraction
Many gap jxn connections= rapid conduction
Many myofibrils= strong contraction

Question 22

Describe the structure-fxn relationship of His bundle, bundle branches and Purkinje fibers.

Answer 22

Fxn: very rapid conduction
Many gap jxn connections= rapid conduction
Few myofibrils= weak contraction