Physio/simple/cardio

Front 1

The SA node spontaneously depolarizes from 60-100 times/min. TRUE/FALSE

Back 1

TRUE. Impulses spread rapidly from the SA node along individual atrial cells to depolarize the right and left atria which then contract.

Front 2

Does the AV node spontaneously depolarize?

Back 2

Yes. It depolarizes more slowly at 40-60 beats/min in the absence of SA node function.

Front 3

Under normal conditions, does the AV node normally depolarize?

Back 3

No. Spontaneous discharge of the AV node and ventricular muscle normally doesnt occur because of CAPTURE of the rhythm by the SA node.

Front 4

The right coronary artery supplies the SA and AV node what % of the time.

Back 4

SA node= 50% of the time.
AV node= 90% of ther time.

Front 5

Sometimes the SA or AV node is supplied by the branches from the left circumflex artery. TRUE/FALSE

Back 5

TRUE.

Front 6

The axon maintains a resting electrical membrane potential such that the outside of the cell is more positive than the inside. TRUE/FALSE

Back 6

TRUE.

Front 7

What does the ATP-driven sodium/potassium pump do?

Back 7

It moves sodium out of the cell and moves potassium in.
In the resting state, therefore the concentration of Na+ ions is much greater outside the cell than inside, and the conc. of K+ is greater inside.

Front 8

What maintains the cellular electrical difference if sodium and potassium are both cations?

Back 8

The pump moves out 3 Na+ for every 2 potassiums that it pumps in. Potassium leaks back outside the cell more easily than sodium leaks back in.

Front 9

In addition to the cellular pump, are there other mechanisms that are voltage dependent?

Back 9

There are infact separate voltage dependent Na+ and K+ channels that are vital to the generation of the action potential.
These channels open or close depending on the state of the membrane electrical potential to allow selective movement of Na+ or K+ and generate a traveling action potential.

Front 10

What is depolarization and how does it come about?

Back 10

In order to fire a neuron, the membrane potential must be partially neutralized by some stimulus to a certain threshold level that is closer to zero than the resting potential. Voltage difference generally requires a change of about 15-35 millivolts.
If the normal potential difference is -60 millivolts, the potential difference may have to be neutralized to -40 millivolts, at which point the local voltage dependent Na+ gate suddenly opens and Na+ rushes into the cell. This is depolarization.

Front 11

What is repolarization?

Back 11

As the impulse spreads, the axon recovers, because the neutralized electric potential quickly triggers not only the shutting off of the voltage dependent sodium gate, but also the opening of a voltage dependent potassium gate. Potassium thus rushes out quickly to help restore the original membrane potential. This is repolarization.

Front 12

What is the refractory period?

Back 12

As the axon recovers along its length as the axon potential travels, the axon cannot fire again until the membrane potential is restored, thus demonstrating a refractory period.

Front 13

Is there a gate for calcium as well/

Back 13

Yes. The concentration normally is much higher extracellularly than intracellularly due to a calcium pump that pumps calcium out of the cell.
Calcium channels operate more slowly than do sodium channels.

Front 14

What are calcium channel effector plateaus?

Back 14

Calcium channels are especially prominent in cardiac and smooth muscle cells where it is desirable to have a relatively
prolonged, complete contraction. calcium channels are much less prominent in axons. a plateau is desirable in the spread of impulses in the cardiac Purkinje fibers, because a plateau creates a refractory period during Purkinje fiber discharge that protects the heart against excessively rapid arrhythmias.

Front 15

How is the SA node self generating?

Back 15

No stimulus is necessary, because there is a spontaneous depolarization. In chemical terms, the slow upsweep is the result of the cell membrane to sodium, which seeps into the cell, resulting in the spontaneous action potential. cells in the AV node have similar qualities but are not quite as leaky as SA node cells.

Front 16

What is the significance of the plateau in atrial muscle?

Back 16

This represents the influence of the slow calcium channels and a prolongation of the time of depolarization. This protects against a too rapid heart rate. It allows enough time for the atrial muscle to contract completely and empty the atria. Ventricular action potentials have an even more prolonged plateau.

Front 17

What exactly is the influence of calcium?

Back 17

It is important in muscle cells, since calcium ions activate the interaction between actin and myosin that is necessary for muscular contraction.