CVS Lecture 5

Membrane permeability to Ca2+ is very high

The membrane is not very permeable to K+ ions

Permeability to Na+ is 20% that for K+

The ease with which the ion passes through the membrane is referred to as conductivity (C)

If the conductance for an ion increases, the ion will pass through the membrane and a current will flow

The resting membrane potential in contractile cells of the atria and ventricles is about -70mV

The inside of the cell is positively charged in relation to the outside of the cell

The resting membrane potential is primarily due to two
things; the high concentration of potassium ions in the intracellular fluid and the high permeability of the cell membrane K+ ions as compared to other ions

The resting membrane potential is close to the equilibrium potential for sodium

Potential reaches threshold: –65 mV

Membrane’s ionic permeability suddenly changes

Cell rapidly depolarises and over shoots to a positive potential of +40mV

At the threshold potential, voltage sensitive potassium channels open very quickly