Topics covered 1.Organization of the nervous system 2.Regions / specialization of the neuron 3.Resting membrane potential Especially ionic basis- Nernst, Goldman, Donnan, active transport 4.Action Potential Especially ionic basis – voltage-gated channels, ionic current, electromotive force 5.Action Potential Conduction Passive spread of current, local depolarization, length constant, role of myelin

The text book –Only topics covered in class –Depth of topics covered in class –But know how to use the information I’ve given

Electrochemical equilibrium –Equilibrium – no net movement –General state where the movement of ions is controlled by concentration gradients and electrical forces Equilibrium potential –The electrical force that occurs at an electrochemical equilibrium

Nernst Equation Equilibrium Potential of X ion (eg. K+) Valence of ion (-1, +1, +2) Faraday constant Gas Constant Temp (  K) Ion Concentration

Nernst Equation What if temperature changed? What if valence of ion changed?

Sample question If two concentrations of KCl solution across a membrane give an equilibrium potential for K + of -60 mV, what will the equilibrium potential be if the concentrations on each side are reversed A.-120 mV B.0 C.+60 mV D.-30 mV Because if [in]>[out], log([out]/[in]) will be negative log([in]/[out]) will be positive

What does it mean for an equilibrium potential to be positive or negative? Indicates direction of electrical force –If negative, +ve charge flow inward –If positive, +ve charge flow outward

Sample Question K = 140 Na = 10 Cl = 30 K = 5 Na = 145 Cl = 110 At rest Vm of this typical cell is -75 mV. What would Vm be if PNa >> Pk,PCl? Answer: Calculate E Na using Nernst equation. Assume Vm  ENa = +67 mV

Goldman equation Typical cell: Pk is 100X PNa therefore Vm  Ek If PNa >> Pk, then Vm  ENa

What if permeability changes? What if ion concentration changes?

Electromotive force –Also called driving force –Difference between Eion and Vm –Determining force if ions flow or not –I = g(Vm-Eion)

Explain the diagram showing the effect of low Na on action potential amplitude

How do we know Na+ important for depolarization? 0 mV -80 mV Replace Na+ in extracellular bath with impermeable cation - choline Normal Low Sodium

Ionic basis –Normal saline E Na = +50 mV –With reduced [Na], E Na will be lower –During AP, Vm  E Na when voltage-gated Na channels open –Therefore if ENa , AP amplitude 

How do we know Na+ important for depolarization? 0 mV -80 mV Normal Low Sodium ENa

Passive Distribution out in [K + ] > [K + ] [Cl - ] < [Cl - ] Equilibrium A- [K + ] in = [A - ] in + [Cl - ] in [K + ] out = [Cl - ] out Since [A-] in is large, [K+] in must also be large +’ve = -’ve

Donnan Equilibrium Example A - = 100 K + = 150 Cl - = 50 A - = 0 K + = 150 Cl - = 150 III Initial Concentrations Are these ions in electrochemical equilibrium? No, E K + = 0 mV E Cl - = -27 mV

Solve for X, X + X 2 = X - X 2 X=30 Let X be the amount of K+ and Cl- that moves

A - = 100 K + = 180 Cl - = 80 A - = 0 K + = 120 Cl - = 120 III Final Concentrations Are these ions in electrochemical equilibrium? Yes, E K + = -10 mV E Cl - = -10 mV space-charge neutrality