Chapter 9 - Cardiac Muscle (Guyton)

Question 1

What is the significance of “plateau” in action potential?

Answer 1

Presence of plateau causes ventricular contraction to last as much as 15 times as long as cardiac muscle as in skeletal muscle

Question 2

Action potential in ventricular muscle fiber

Answer 2

105 millivolts

Note: it rises from a very negative value of -85 millivolts to +20 millivolts during each beat

Question 3

Difference between action potential of cardiac and skeletal muscle ?

Answer 3

• action potential in skeletal muscle is caused by entirely “fast sodium channels”
• in cardiac muscle action potential is caused by “fast sodium channels” as well as “slow calcium channels” also called as “sodium-calcium channels”

Question 4

What causes the decrease in potassium permeability in cardiac muscle?

Answer 4

Excess of calcium influx through the calcium channels

Question 5

Normal refractory period of ventricle is?

Answer 5

.25 to .30 second
Note: there is an additional .05 second of refractor period during which the muscle is more difficult than normal to excite

Question 6

Calcium release channels are also known as?

Answer 6

Ryanodine receptor channels

Question 7

Potentials in arterial and ventricular syncytium are connected via?

Answer 7

A-V bundle