Mod 4

In which phase of the ventricular muscle action potential is the potassium permeability highest? 2 0 4 1 3

3

What is the "funny current?" What is its importance to cardiac conductance?

Channels permeable to Na+ and K+ and is activated by hyperpolarization and has an inward current of Na+ it is responsible for spontaneous diastolic depolarization. It controls the rate of SA node activity and therefore controls heart rate which allows for the automaticity of the heart.

The membrane electrical potential at which the inward flow of an ion is equal to its outward flow best describes a given ion's _________ Nernst number voltage concentration gradient diffusional gradient equilibrium potential

Equilibrium potential

This ion channel opens at a voltage of about -40mV Na+ channel L-Type Ca++ channel Delayed rectifier K+ channel IKr Na+/K+ mixed conductance "funny" channel T-Type Ca++ channel

L type ca channels

The ionic gradient across a heart cell membrane at rest favors K+ moving ________ and Na+ moving ________ the cell. Outside/Inside Inside/Outside

Outside/inside

Which anatomical segment in the heart has the highest conduction velocity? Which is the slowest? What is the physiological relevance?

Punkinje

What channel(s) is(are) responsible for the "plateau" phase (Phase 2) of cardiac muscle cell action potentials? Describe the importance of this phase to normal cardiac function.

Slow L-type Ca++ channels and delayed K+ rectifier channels are responsible for the plateau phase. These are responsible for the influx of Ca++ and the efflux of K+. This sets up for repolarization of the cell.