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Exam 2: Ch. 2

Terms in this set (35)

What does the coordination of cardiac muscle cells activity depend on?
the electrical stimulus that is regularly initiated at an appropriate rate and reliably conducted through the entire heart.
Mechanical pumping action depends on a robust contraction of the muscle cells that result in repeating cycles of what?
- tension development
- shortening
- relaxation
In all striated muscle cells, what is contraction triggered by?
a rapid voltage change called an action potential
Where does action potential occur?
the cell membrane
How does cardiac muscle cell's action potential differ from skeletal muscle cells that promote synchronous rhythmic excitation of the heart?
- they can be self-generating
- they can be conducted directly from cell to cell
- they have a long duration, which precludes fusion of individual twitch contractions
What do all cells have across their membrane?
electrical potential (voltage)
What is transmembrane potentials caused by?
a separation of electrical charges across the membrane itself.
How can transmembrane potential change?
for electrical charges to move across the cell membrane.
What is current cross the membrane carried by?
by the movement of ions through the cell membrane
What are the most important ions of cardiac transmembrane potential?
- sodium (Na+)
- calcium (Ca2+)
- potassium (K+)
What is the concentrations of the important ions of cardiac transmembrane potential?
- Na and Ca are more concentrated in the interstitial fluid than they are inside cells

- K+ is more concentrated in intracellular then interstitial fluid
What are the types of transmembrane protein structures that are involved in ion movement across the cell membrane?
- ion channels
- ion exchangers
- ion pumps
What is responsible for the resting membrane potential and for the rapid changes in membrane potential that constitute the cardiac cell action potential?
ion channels
What is the net result of the status of membrane channels to a particular ion?
membrane's permeability to that ion
What does high permeability to sodium mean?
of the status of ion channels accounts for the characteristics membrane potential change that occurs when cardiac cells are activated.
What do positive and negative ions do in the cell?
- Positive ions will diffuse out of the cell

- Negative ions cannot leave the cell because the membrane is impermeable to them
What are the normal concentrations of K+?
145 mM K+ inside cells

4 mK K+ in the extracellular fluid

-90 mV for K+ equilibrium potential
What is the cell membrane to charged ionic species?
It is impermeable, which means that K+ inside of the cell can't get out and the K+ outside of the cell can't get in. (needs a K+ leak channel)

Example: This classroom is impermeable to all the students when the doors are closed because you can't walk through a wall. You need a door (leak channels).
What does K+ leak channels mean for the K+ inside and out of the cell?
There will be high concentration of K+ inside the cell and a low concentration of K+ outside of the cell.
What is K+ efflux is due to?
K+ moving out of the cell is due to the concentration gradient
What happens every time a positive ion (K+) leaks out?
it makes the inside of the cell more negative
What happens to the K+ that was leaking out when there is a lot of negative charge inside of the cell?
the K+ that was leaking out gets attracted back inside.
What happens when you make the inside of a cell negative?
The positive end the attracks the negative end (vise versa).

Just like the opposite ends of a magnet.
What is the K+ influx is due to?
electrochemical gradient
How negative does the inside of a cell have to be for K+to come back in?
Equilibrium Potential, the charge at which K+ efflux = K+ influx

In other words, the charge inside of the cell that will balance the concentration gradient
What is the Nernst equation?
...
Why would Na want to go out of the cell?
because of the concentration gradient, which makes a negative charge but then will pull it back in because of the equilibrium potential (-96).
When Na influx occurs because of the concentration gradient, what charge is it bringing with it?
With sodium influx, it will come in with a positive charge. You will continue to get these positive charges coming in. Eventually, when you already have a bunch of positive charges inside the cell, and more try to come in, the positive charges will repel each other and get spit back out.
Na efflux is due to what?
Electrochemical gradient (equilibrium)
How much positive charge do you need in order to balance concentration gradient?
use the equation (look up and put here)
What is reasonable RMP?
-70
Goldman-Hodgkin-Katz equation?
...
Why would -96 weighs more than +66?
because -96 is closer to -70
What thing's could alter the resting membrane potential of a cell?
- Can the extracellular K+ membrane alter the cell? Yes, because if you change your extracellular K+, it will change your equilibrium potential for K+.

- Changes in extracellular Na

- Change in the conduction ratio
What is the conduction ratio?
the amount of K+ per all channels (or sodium)
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