Heart Electrical Properties (03)

Question 1

SA node

Answer 1

sinoatrial node. Generate spontaneous action potentials. Action potentials pass to atrial muscle cells and to the AV node

Question 2

AV node

Answer 2

atrioventricular node. Action potentials conducted more slowly here than in any other part of system. Ensures ventricles receive signal to contract after atria have contracted

Question 3

AV bundle

Answer 3

passes through hole in cardiac skeleton to reach interventricular septum

Question 4

Right and left bundle branches

Answer 4

extend beneath endocardium to apices of right and left ventricles

Question 5

Purkinje fibers

Answer 5

Large diameter cardiac muscle cells with few myofibrils. Many gap junctions. Conduct action potential to ventricular muscle cells

Question 6

Depolarization

Answer 6

voltage gated Na+ channels open, rapid inflow

Question 7

Plateau

Answer 7

(maintained depolarization) due to Ca2+ inflow when voltage-gated slow Ca2+ channels open and K+ outflow when some K+ channels open

Question 8

Repolarization

Answer 8

closure of Ca2+ channels and K+ outflow when additional voltage-gated K+ channels open

Question 9

Cardiac action potentials

Answer 9

Conducted from cell to cell

Question 10

Skeletal action potentials

Answer 10

Conducted along length of single fiber

Question 11

Cardiac rate of action potential propagation

Answer 11

Slow because of gap junctions and small diameter of fibers

Question 12

Skeletal rate of action potential propagation

Answer 12

Faster due to larger diameter fibers

Question 13

Autorhythmicity: SA Node Action Potential

Answer 13

1. Pacemaker potential (Na + “leakage” into cell)
2. Depolarization (More Ca 2+ channels open, K+ channels closed)
3. Repolarization (Ca 2+ channels close, K+ channels open)

Question 14

Components of ECG graph

Answer 14

• P wave
• QRS complex
• T wave
• PQ/PR interval
• QT interval