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Electrochemistry of the Nerve CellNeurons are both electrical and chemical devices. Understanding the basic electrochemistry of nerve cells serves as the foundation for understanding all of a neuron's important electrical properties. Key ideas for this unit:
Equilibrium versus Steady State
A Simulation Program for Understanding ElectrochemistryFigure 1: The Nernst Simulator
The Three Conditions for Membrane EquilibriumThree conditions must be satisfied to ensure equilibrium across a membrane: We will now explore each of these conditions by setting up different conditions on either side of a membrane, and see how the results unfold, as well as how we can capture these ideas mathematically so that we can predict the outcome in advance of doing the experiment. Diffusion and Concentration GradientsLet's first examine an apparently very simple situation: a membrane that is permeable to water, which is placed between two compartments filled with water. Figure 2: Water and semi-permeable membrane
Figure 3: Glucose and semi-permeable membrane
Problem 1: Diffusion and Concentration GradientsYou now have enough information to work on Problem Set 1, Problem 1. Please do so now. Osmotic BalanceThe problem shown in Figure 3 becomes more interesting if we assume that water can freely move from one side of the membrane to the other, but glucose cannot.
Figure 4: Cell in an isotonic bath
ElectroneutralitySo far, we have dealt with uncharged particles. In water, however, many molecules that are bound together ionically can form weak bonds with water molecules.
Figure 5: Unequal concentrations of charged particles on each side of a membrane
Balancing Concentration and Electrical Gradients: The Equilibrium or Nernst PotentialHow would one create a selectively permeable ion channel?
Figure 6: Balancing osmotic pressure, bulk electroneutrality, and concentration and electrical gradients
Setting Up an Equilibrium PotentialThe process by which a single ion (potassium) sets up an equilibrium (Nernst) potential across the membrane Understanding Hyperpolarization and DepolarizationCharge separation across the membrane, hyperpolarization and depolarization Membrane Potential and the Effects of Changing Concentrations vs. Injecting CurrentCharge separation across the membrane, hyperpolarization and depolarization What factors influence the movement of ions across a cell membrane?Two factors determine the net flow of ions across an open ionic channel: the membrane potential and the differences in ion concentrations between the intracellular and the extracellular spaces.
What prevents ions from moving across the membrane?Phospholipid Bilayer Prevents Ion Movement
The hydrophilic heads of the molecules align on the outside of the membrane, interacting with the intra- and extracellular solution of the cell, whereas the hydrophobic tails are arranged in the middle, forming a barrier to water and water-soluble molecules like ions.
What is flux in membrane potential?Net flux. Membrane potential. Definition: The voltage difference across a cell plasma membrane. The membrane potential is generally inside negative with respect to the outside, where the outside potential is generally set as the reference value.
Which of the following can influence the rate at which a molecule will move across the plasma membrane?The ability of a molecule to travel across a membrane depends on its concentration, charge and size. In general, molecules diffuse across membranes from areas of high concentration to low concentration.
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