Cardiac Muscle

Question 1

What do cardiac parasympathetic fibers release? What nerves do they act through?

Answer 1

ACh

Vagus Nerves

Question 2

What does ACh do in the cardiac fibers?

Answer 2

• Increases permeability of resting membrane to K+

- Decreases diastolic i(f) current through HCN channels

Question 3

What is the NET EFFECT of cardiac parasympathetic fibers?

Answer 3

• SLOWS HR (prolongs tim toe depolarization)
• “Negative Chronotropic Effect”
• Slows rate of spontaneous depolarization of membrane
• Initial hyperpolarization of resting membrane potential

Question 4

What do cardiac sympathetic fibers release?

Answer 4

Norepinephrine (NE)

-Increase diastolic inward currents i(f) through HCN channels

Question 5

What is the NET EFFECT of cardiac sympathetic fibers?

Answer 5

-SPEEDS HR
(shortens time to depolarization!)
-“Positive Chronotropic Effect”
-Increases rate of spontaneous depolarization of membrane

Question 6

What is preload?

Answer 6

Passive/resting tension placed on cardiac muscle cells BEFORE contraction. (A fxn of the volume and pressure at the end of diastole) - generated by filling of the heart - this pressure and tension!

Question 7

What conditions is preload increased in?

Answer 7

Hypervolemia (too much fluid in the blood), Regurgitation of cardiac valves, heart failure

Question 8

What is afterload?

Answer 8

Active tension placed on cardiac muscle cells DURING contraction. (A function of the resistance the left ventricle must overcome to circulate blood)

Question 9

What conditions is afterload increased in?

Answer 9

Hypertension, vasoconstriction

Question 10

Calcium binds to ___ and serves a critical role in muscular contraction.

Answer 10

Troponin