Cardiac contractility and the event s of the cardiac cycle

Question 1

How much bigger are cardiac muscle’s T-tubules in comparison to skeletal muscle?

Answer 1

5x greater in diameter and 25x greater in volume

Question 2

What is the refractory period?

Answer 2

A period immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation.

Question 3

What is the absolute refractory period?

Answer 3

The period of time during which a second action potential ABSOLUTELY cannot be initiated, no matter how large the applied stimulus is

Question 4

What is diastole?

Answer 4

The period of relaxation of the heart

Question 5

What is systole?

Answer 5

The period of contraction of the heart

Question 6

What percentage of ventricular filling is due to contraction of the atria?

Answer 6

20%

Question 7

What is the absolute refractory period in cardiac muscle?

Answer 7

245ms

Question 8

Why is blood pressure the pulmonary circulation much lower?

Answer 8

• There is much less resistance to flow
• Right side of the heart needs to do less work
• Right ventricle walls contain less muscle mass

Question 9

What is the blood pressure in pulmonary circulation?

Answer 9

30mmHg / 12mmHg

Question 10

What is the end systolic volume (ESV)

Answer 10

Volume in the ventricle at the end of systole

Question 11

What is the end diastolic volume (EDV)

Answer 11

Volume in the ventricle at the end of diastole

Question 12

How is stroke volume calculated?

Answer 12

EDV-ESV

Question 13

What is the absolute refractory period of cardiac muscle?

Answer 13

245ms

Question 14

What is the period of contraction of cardiac muscle?

Answer 14

250ms

Question 15

What is the cardiac output?

Answer 15

Volume of blood pumped by the heart (L/min) (SV x HR)

Question 16

When does the AV valve open?

Answer 16

When the atrial pressure exceeds the ventricular pressure

Question 17

When does the AV valve close?

Answer 17

When the ventricle pressure exceeds the atrial pressure

Question 18

What is the isovolumic (isometric) contraction?

Answer 18

The period of time during ventricular contraction where both the semilunar and AV valves are closed leading to an increased ventricular pressure.

Question 19

What is the period of supranormal excitability?

Answer 19

The period at the end of phase 3 of the action potential during which activation can be initiated with a milder stimulus than is required at maximal repolarization, because at this time the cell is excitable and closer to threshold than at maximal diastolic potential.