##### Membrane 4 (WS 6)

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1

Electricity

1. Law of conservation of electrical charges
2. Opposite charges ATTRACT; like charges REPEL each other
3. Separating positive charges from negative charges requires ENERGY
4. Conductor vs. insulator- keeps charge separated; can also conduct a charge

The cell membrane acts as an insulator to prevent free movement of ions

2

Membrane Potential

is the electrical difference across a cell membrane (a difference of a small fraction of a Volt)

All living cells have a membrane potential
Nerve and muscle cells can vary membrane potential- a special characteristic
Outside by conventions is set at 0 mV; inside has a slightly negative potential difference (-65 to -85 mV)

3

Resting Membrane Potential

RMP

Potential across resting (stable) cell membrane
Is typically -60 to -85 mV (depending on the cell type)
Is polarized- a negative charge

4

Describing (Types) of Membrane Potentials

1. Resting Membrane Potential (RMP)
2. Equilibrium Potential
3. Pacemaker

5

Equilibrium Potential

a type of membrane potential

Needs an electric potential to perfectly balance (neutralize) a given ion concentration gradient across a membrane
E[ion symbol] represents
EX: ENa+

The potential difference (electrical gradient) is equal and opposite the concentration gradient for a specific ion.
Net flux of the ion is zero at the E[ion symbol]

6

Nernst Equation

For Equilibrium Potential

Predicts equilibrium membrane potential for single ion.
The potential is influenced by a concentration gradient of ion and membrane permeability of ion
Equation:
Ex= 61log [Xo]
z [Xi]

Xo= outside concentration for ion X
Xi= inside concentration
z= the valence of the ion

7

Goldman Hodgkin Katz Equation

***Just recognize it***

Similar to Nernst but more inclusive

works with Sodium, Potassium,and Chloride

Tells membrane potential, NOT equilibrium
Predict membrane potential using multiple ions
Placement of membranes can affect its potential to be more or less excitable

8

Membrane potential terminology

Depolarization- moving toward the positive (toward zero)