The initial rapid repolarization of the cardiac action potential from a ventricular myocyte cell is due to _____ channel inactivation and outward flow of _____ (_____ channel).
*to = transient outward
In phase 1 of the ventricular myocyte action potential, voltage-gated _____ Ca2+ channels open in response to depolarization. This slows down the repolarization brought about by the opening of K+ channels.
After the initial opening of potassium channel, another group of channels called _____ channels opens to return the membrane to resting level (ventricular myocyte action potential).
During the resting phase, there is a small inward current of Na+ through _____ channels and small K+ outward current by _____ channels (ventricular myocyte action potential).
Cardiac action potentials travel from cell to cell via low resistance _____.
Why do cardiac action potentials travel in one direction?
The cell that depolarizes an adjacent cell undergoes a refractory period.
During the _____, a cardiac action potential cannot occur.
absolute refractory period
Repeated stimulation of the motor nerve results in large _____ contractions.
What kind of muscle cannot create sustained tetanic contractions?
Phase 4 of the SA node action potential is known as the _____. It occurs due to the inward _____ current (_____ channel) and inward _____ current (_____ channel).
What type of Ca2+ channels are involved in phase 4 of the SA action potential?
T-type Ca2+ channels
When depolarization of the SA node action potential reaches its threshold, _____ Ca 2+ channels open while _____ channels begin to close.
Phase 3 of the SA node action potential is known as _____. This is due to closure of _____ channels and opening of _____ channels.
In the SA node action potential, the upstroke of action potential is due to the inward _____ current (rather than the inward _____ current).
The rate of _____ of the SA node sets the heart rate.
In the heart, there is a delay in conduction through the _____. This occurs because cells in this structure have higher _____.
The _____ is the only electrical contact between the atria and ventricles.
Do the atria or ventricles contract first?
The word "sinus" refers to which node of the heart?
Damaged myocardial muscle cells can generate action potentials spontaneously, leading to _____.
Which phase of the cardiac action potential will the parasympathetic nervous system act upon?
Acetylcholine activates _____ receptors to activate _____ proteins. This opens _____ channels and increases _____ conductance, which will cause hyperpolarization. The overall effect is to prolong phase _____ of the SA node.
Acetylcholine can impact the heart in 2 ways. In one pathway, it activates _____ proteins and decreases the enzyme _____. This leads to a decrease in _____ concentrations, which will subsequently lower the enzyme _____. The result is decreased activation of _____ and _____ channels, which slows the rate of spontaneous depolarization of the SA node. Ultimately, these actions prolong phase _____ of the SA node.
protein kinase A
To calculate heart rate from an ECG record, measure the time between the ____ waves.
Sympathetic effects on the SA node: Norepinpehrine acts upon cardiac _____ receptors to increase the molecule _____, which induces phosphorylation of _____ and _____ channels. This increases the rate of depolarization and increases heart rate.
In an ECG, the P wave corresponds to depolarization of _____. It is the _____ deflection, and its duration is the time it takes to depolarize the _____ myocardium.
The P-R interval corresponds to the interval between _____ and _____ activation. Thus, it can be used to record the conduction time between the SA node and ventricular myocardial cells.
The QRS complex corresponds to _____ depolarization. Its duration is the time to depolarize _____.
Which is larger: QRS complex or P wave? Explain.
QRS complex > P wave because the ventricular mass > atrial mass
In ECG, _____ is any initial downward deflection followed by an upward deflection.
In ECG, _____ is any upward deflection whether or not it is preceded by a Q wave.
In ECG, _____ is any downward deflection preceded by an R wave.
The _____ segment corresponds to the plateau of ventricular action potential. All regions of the ventricles are completely _____.
In ECG, the _____ corresponds to repolarizaton of the ventricle.
The _____ interval is between the onset of the QRS complex and end of T wave.
The _____ interval provides a useful index of ventricular action potential duration.
Prolonged _____ interval can lead to arrhytmias and death.
During the _____ interval, all cardiac cells are resting.