Cardiac Muscle Action Potential Channels

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What is the primary mechanism for regulating the amount of calcium that enters the cell during depolarization?

Binding of norepinephrine to muscarinic receptors

Inhibition of adenylyl cyclase

Phosphorylation of the L-type calcium channel (correct)

Hydrolysis of cAMP to ATP

Which receptor is primarily coupled to a specific stimulatory G-protein that activates adenylyl cyclase?

Beta-1 adrenoceptor (correct)

Gi-protein

Adenosine receptor A1

M2 muscarinic receptor

What effect does the inhibitory G protein (Gi-protein) have on inotropy?

Increases inotropy

Decreases inotropy (correct)

Stimulates adenylyl cyclase

No effect on inotropy

What is the primary function of cardiac myocytes?

To contract repetitively Signup and view all the answers

Where is the sinus (sinoatrial) node located?

Superior posterolateral wall of the right atrium Signup and view all the answers

What is the resting membrane potential of the sinus nodal fiber between discharges?

-55 to -60 millivolts Signup and view all the answers

What is the term used to describe the fusion of cardiac myocytes resulting in a branching network of cells?

Functional syncytium Signup and view all the answers

What serves as low resistance pathways between cardiac myocytes, permitting cell-to-cell conduction of electrical currents?

Gap junctions Signup and view all the answers

Which type of muscle has a branching network of cells sometimes referred to as a functional syncytium?

Cardiac muscle Signup and view all the answers

What are the specialized cell membranes that connect individual cardiac myocytes to each other?

Intercalated disks Signup and view all the answers

Which type of muscle shares some structural and functional similarities with cardiac muscle?

Skeletal muscle Signup and view all the answers

What ensures that an electrical impulse will travel to all interconnected cardiac myocytes when one myocyte is electrically stimulated?

Gap junctions Signup and view all the answers

What causes the rapid upstroke spike of the action potential observed in ventricular muscle?

Opening of the fast sodium channels Signup and view all the answers

What causes the 'plateau' phase of the ventricular action potential?

Opening of the slow sodium-calcium channels Signup and view all the answers

Why is the resting potential of sinus nodal fibers less negative than that of ventricular muscle fiber?

Influx of positive sodium and calcium ions through leaky cell membranes Signup and view all the answers

What causes hyperpolarization in the sinus nodal fibers?

Activation of potassium channels Signup and view all the answers

What is the primary role of the atrioventricular (A-V) node?

To delay the transmission of the cardiac impulse into the ventricles Signup and view all the answers

What is the velocity of conduction in most atrial muscle fibers?

0.3 m/sec Signup and view all the answers

What is the main cause of the slow conduction in the transitional, nodal, and penetrating A-V bundle fibers?

Diminished numbers of gap junctions between successive cells Signup and view all the answers

What is the velocity of action potential transmission in the Purkinje fibers compared to the usual ventricular muscle fibers?

1.5 to 4.0 m/sec Signup and view all the answers

What is the discharge rate of the Purkinje fibers?

15 to 40 times per minute Signup and view all the answers

Why does the sinus node control the beat of the heart?

Its rate of rhythmical discharge is faster than any other part of the heart Signup and view all the answers

What allows almost instantaneous transmission of the cardiac impulse throughout the entire remainder of the ventricular muscle?

Rapid transmission by Purkinje fibers Signup and view all the answers

What is the intrinsic rhythmical discharge rate of the A-V nodal fibers?

40 to 60 times per minute Signup and view all the answers

What is particularly true about a few other parts of the heart, similar to the sinus nodal fibers?

They can exhibit intrinsic rhythmical excitation Signup and view all the answers