Diffusion and Membrane Potential

ch.3 pg 63-65, 77-84 Action and Graded potential ch.4 87-102

Explain equilibrium and resting membrane potentials

What is the concept of diffusion

Identify the differences between leak channel and Na+/K+ ATPase

What is diffusion?

the process of movement of molecules under a concentration gradient

Net movement in diffusion

is the overall flow of particles from a region of higher concentration to a region of lower concentration driven random molecular motion until equilibrium is reached

What factors affect the rate of net diffusion

1. Magnitude (of concentration gradient) - as increase concentration gradient, increase rate of diffusion

2. Permeability (of the membrane) - increase of permeability, increase rate of diffusion

3. Surface area (of the membrane) - increase surface area, increase rate of diffusion

4. Molecular weight (of the substance) - increase molecular weight, decrease rate of diffusion

5. Distance (over which diffusion takes place -thickness) - increase distance, decrease rate of diffusion

What is electrochemical gradient?

diffusion down a concentration (chemical) gradient —> high to low concentration

movement along an electrical gradient

what are neurons?

nerve cells thay specialized for electrical signaling over long distances

What is membrane potential (Vm)?

Membrane potential is a spearation of opposite charges across the plasma membrane

How does the cell create charge separation for K+ and Na+?

1. Equilibrium membrane potential for K+

2. Equilibrium membrane potential for Na+

How does the cell create charge separation?

1. Establishes and maintains concentration gradients for key ions (Na+, K+)

2. Ions diffuse through the membrane down their concentration gradients

3. Diffusion through the membrane results in charge separation, creating a membrane potential (electrical gradient

4. Net diffusion continues until the force exerted by the electrical gradient exactly balances the force exerted by the concentration gradient

5. This potential that would exist at this equilibrium is “equilibrium potential”

Process of Equilibrium potential for K+

1. K+ tends to move out of the cell

2. Outside of the cell becomes more positive

3. Electrical gradient tends to move K+ into the cell

4. Electrical gradient counterbalances gradient

5. No further net movement of K+ occurs

Process of Equilibrium potential for Na+

1. Na+ tends to move into the cell

2. Inside of the cell becomes more positive

3. Electrical gradient tends to move Na+ out the cell

4. Electrical gradient counterbalances concentration gradient

5. No further net movement of Na+ occurs

Nerst Equation

equation describing the equilibrium potential for a particular ion (i)

where R is the gas constant, T is the temperature in degrees Kelvin, z is the valence of the ionic species, & F is the Faraday constant

Resting Membrane Potential

1. K+ high in the ICF and Na+ high in the ECF

2. K+ drives equilibrium potential for K+

3. N+ drives equilibrium potential for Na+

How do K+ and Na+ penetrate the cell membrane?

Leak channels - permit ions to flow down concentration gradients

Why is Na+ higher outside of the cell and K+ higher inside the cell?

Na/K ATP ase - establishes and maintains concentradtion gradients

Concentration Gradient

Na+/K+ ATPase establishes the unequal distribution of Na+ and K+ ions inside and outside of the cell

Action Graded Potential

Understand the process involved with depolarization and hypolarization

Describe the differences between voltage-gated Na+ and K+ channels

Understand the roles of refractory periods

Describe the differences between action potential and graded potential

Depolarization

change in membrane polarization to more positive values than resting potential

Hyperpolarization

change in membrane polarization to more negative values than resting membrane potential

Action potential

Brief all-or-nothing reversal in membrane, potentialm (spike), lasting on the order of 1 millisecond that is brought about by rapid changes in membrane permeability, to Na+ and K+ ions