# Chapter 4 The Action Potential

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Chapter 4 The Action Potential

Nernst Relation [ion] out [ion] in E = mV log10

Goldman Equation Pk[Ko] + PNa[Nao] Pk[Kin] + PNa[Nain] Vm = 60 log10

Time Course of Action Potential

Injecting Current into Neuron

Frequency vs Depolarization

Membrane Currents and Conductances

Flipping Potential by Changing Conductance

Sodium Channel Structure

Na Selectivity Filter

Depolarization Changes Configuration

Polarization Opens Na Channel

Question 1 A new monovalent ion, zirconium, is found to be 100 times more concentrated outside than inside the neural membrane. The neuron has channels that are selectively permeable to zirconium. What is the equilibrium potential for zirconium? +60 mV, -60 mV, +90 mV, -90 mV, +120 mV, -120 mV.

Question 2 At the normal resting state there is no net current through the membrane. What is the Na/K pump doing? nothing, moving ions out, moving ions in, moving some ions in and moving others out

Question 3 During the action potential, the sodium current is terminated by the sodium inactivation gate. How is the potassium current terminated? Potassium inactivation gate b. membrane voltage c. depletion of potassium ions, d. it’s not terminated

Question 4 When a membrane is “charged” and maintains a voltage across it, most of the ions responsible for the charge are located just adjacent to the membrane. This distribution exists because: The membrane is sticky for ions, ions are repelled by the cytoplasm, ions are attracted to the other side of the membrane, ions like to accumulate near the ion-selective channels.

Patch Electrode Channel

Channel Openings

Inward Na and Outward K Currents

Time Course of Action Potential

Propagation

Propagation

Electrotonic Decay

Myelination

Nodes of Ranvier

Site of Action Lidocaine

Density of Channels = Site of Initiation