Heart Excitation

Question 1

Where does the longest delay occur?

Answer 1

at the AV node

Question 2

Why does the longest delay occur at the AV node?

Answer 2

because of few gap junctions (increased resistance).

Question 3

When does the SA node fire?

Answer 3

before the P wave

Question 4

When does atrial action potential occur?

Answer 4

during the P wave

Question 5

When does ventricular action potential occur?

Answer 5

during the QRST waves.

Question 6

What is a difference in calcium channels between cardiac and skeletal muscle?

Answer 6

cardiac muscle has slow calcium receptors that stay open for a period of time.

Question 7

Does the SA fiber or ventricular fiber have a higher amplitude?

Answer 7

ventricular

Question 8

What does parasympathetic innervation to the heart do?

Answer 8

decreases the rhytmicity of the SA node.

Question 9

What does the sympathetic innervation of the heart do?

Answer 9

increases vesicle contraction via norepinephrine.

Question 10

When does isovolumic contraction occur?

Answer 10

Above 80 mm Hg; after the AV valve has closed and the aortic valve has opened.

Question 11

What is diastasis?

Answer 11

Midpoint of diastole in which blood enters the ventricle slowly or ceases to enter prior to atrial systole.

Question 12

When does isovolumic relaxation occur?

Answer 12

When the aortic valve is closed and the AV valve is opened.

Question 13

How much blood flows from the atria to the ventricles before the atria can contract?

Answer 13

80%; remaining 20% after contraction.

Question 14

What valve is closed during a systole?

Answer 14

AV

Question 15

What valves open at the end of a systole?

Answer 15

AV

Question 16

What are the steps of the cardiac cycle?

Answer 16

Rapid filling, diastasis (small blood flow from atria), last 20% (atrial contraction), isovolumic contraction (by ventricles).

Question 17

What is contracting during an isolvolumic contraction?

Answer 17

ventricles

Question 18

When does rapid ejection occur?

Answer 18

Above 80 mm Hg (during first third of contraction).

Question 19

How is ejection fraction calculated?

Answer 19

SV\EDV

Question 20

How can stroke volume be increased?

Answer 20

Increased EDV or decreasing ESV

Question 21

What causes an increased stroke volume?

Answer 21

An increased preload

Question 22

What kind of relationship is there between output and pressure?

Answer 22

An increased pressure causes a decreased output.

Question 23

How long does it take to send a signal from the sinus node to the AV node?

Answer 23

.16 seconds