1. Ion Flow: current across membrane;

2. Charge Separation: separating charge across membrane creates potential energy; P.M. = insulator

3. Channels (Conductor): integral/transmembrane proteins imbedded in P.M. open which allow ions to flow; Passive (leakage)-always open, allowing specific ions to flow through; Active (gated)- only open when stimulated (chemically or voltage gated)

4. Current Flow: depends on ELECTRICAL CHARGE MOVEMENT (charged ions move toward area of opposite charge) and CHEMICAL DIFFUSION (ions diffuse from h-l concentration); Together these forces are known as the Electrochemical Gradient

1. Potential Energy: separation of positive and negative charges; voltage

2. Kinetic Energy: alllows separated charges to move freely; current

3. Resistance: force which slows down current flow; Insulator (inhibits flow) & Conductor (promotes flow)

4. Ohm's Law: voltage/resistance= current (I=V/R)

When cell is at rest (not conducting APs), the plasma membrane can create a potential enegy situation; potential energy is created due to chemical and electrical forces;

-Composition: Different ions with different concentrations and different charges; cell is electrically neutral inside, but plasma membrane has charge of ~ -70mV at its RMP

-Generation and Maintenance: Polarization (basis of all electrical conductivity of cells)

Specific ions separate themselves at different concentrations immediately around the membrane;

• [Na+] higher outside
• [K+] higher inside
• [A-] (negatively charged particle) higher inside
• [Cl-] higher outside

Movement of ions through:

1. Na/K ATPase: in P.M; requires ATP to pump ions against concentration gradient; 3 Na+ out, 2 K+ in; maintains unequal distribution of ions --> fuels electrochemical gradient

2. Passive K+ channels: More passive K+ channnels than Na+ channels and K+ moves more freely than Na+; Potassium is typically pumped into cell by ATPase so it naturally wants to move out along concentration gradient, Sodium wants to move in but is not easily permitted. This causes unequal concentration gradient

Cells that change their membrane potential have gated channels which open/close in response to stimuli, allowing ions to flow across membrane;

1. Polarized: charge separated across membrane; RPM = -70mV

2. Depolarized: charge allowed to flow (+ to interior); not polar- charge is approaching 0mV

3. Hyperpolarized: charge more separated than normal (more polarized than RMP); potential energy is greater; + charge leaving cell

4. Repolarized: return polarity to baseline; return from hyperpolarization- decrease potential energy; return from depolarization- increase potential energy

Done in 2 ways: Graded and Action Potentials (need gated-channel proteins for these potentials)

-Graded Potential: capable of conducting graded potentials through chemically-gated channels; channels open by chemical stimulus binding to transmembrane protein/receptor; limited # of ions flow through and area of channels is small

-Action Potential: capable of conducting action potentials through voltage-gated channels; channels open by change in potential energy; large amount of ions move flow through entire length of cell (all or nothing); often initiated by graded potentials; 4 phases

1. Resting: RMP esists; closed gated channels

2. Depolarization: Active phase; chemically-gated channels open, Na+ enters (depolarizing) which initiates voltage-gated channels to open

3. Repolarization: Active phase; Na+ channels close (C-G channels have already closed); K+ voltage-channels open (lots of K+ driven out by concentration gradient)

4. Hyperpolarization: Active phase; K+ channels stay open too long, causing more negative charge than RMP;

Na/K ATPase restores cell to RMP (-70mV)

Happens down length of cells, may go down in 2 directions (ex: muscle cell) or 1 direction (ex: nerve cell); once channel ends, action potential can no longer propagate

Must have enough stimulus to open the voltage-gated channels; a chemical stimulus sometimes does not cause enough sodium to enter, preventing the sodium-voltage gates from opening (graded potential wasn't enough)

Once gated channels open, AP goes all the way down length of cell where there are gated channels

Length of time where AP was just completed and there is hyperpolarized or repolarized membrane; all ions need to be returned to baseline by Na/K ATPases

1. Absolute: immediately after AP; membrane incapable of stimulus response (ions on wrong side)

2. Relative: slightly later when Na/K ATPase have had time to restore concentrations; possible for a large stimulus to generate AP on a partially restored membrane