Heart Excitation Flashcards
Where does the longest delay occur?
at the AV node
Why does the longest delay occur at the AV node?
because of few gap junctions (increased resistance).
When does the SA node fire?
before the P wave
When does atrial action potential occur?
during the P wave
When does ventricular action potential occur?
during the QRST waves.
What is a difference in calcium channels between cardiac and skeletal muscle?
cardiac muscle has slow calcium receptors that stay open for a period of time.
Does the SA fiber or ventricular fiber have a higher amplitude?
ventricular
What does parasympathetic innervation to the heart do?
decreases the rhytmicity of the SA node.
What does the sympathetic innervation of the heart do?
increases vesicle contraction via norepinephrine.
When does isovolumic contraction occur?
Above 80 mm Hg; after the AV valve has closed and the aortic valve has opened.
What is diastasis?
Midpoint of diastole in which blood enters the ventricle slowly or ceases to enter prior to atrial systole.
When does isovolumic relaxation occur?
When the aortic valve is closed and the AV valve is opened.
How much blood flows from the atria to the ventricles before the atria can contract?
80%; remaining 20% after contraction.
What valve is closed during a systole?
AV
What valves open at the end of a systole?
AV
What are the steps of the cardiac cycle?
Rapid filling, diastasis (small blood flow from atria), last 20% (atrial contraction), isovolumic contraction (by ventricles).
What is contracting during an isolvolumic contraction?
ventricles
When does rapid ejection occur?
Above 80 mm Hg (during first third of contraction).
How is ejection fraction calculated?
SV\EDV
How can stroke volume be increased?
Increased EDV or decreasing ESV
What causes an increased stroke volume?
An increased preload
What kind of relationship is there between output and pressure?
An increased pressure causes a decreased output.
How long does it take to send a signal from the sinus node to the AV node?
.16 seconds
