Lectures3+4-Chapter_2-BiologicalFoundations

Anions negatively charged ions cations positively

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Unformatted text preview: of the neuron. Anions = negatively charged ions Cations = positively charged ions Diffusion = the tendency for molecules to distribute themselves so that they have the same concentration everywhere in their environment (tend to move from areas of higher concentration to areas of lower concentration, where they bump into each other less) Why Neurons Have Negative Resting Membrane Potentials Numbers show CONCENTRATIONS, not charges Net charge difference based on concentration differences in charged molecules between inside and outside of cell (Organic, mostly negatively-charged molecules only found inside the cell, which can’t diffuse out of it) Positively charged ions (cations), such as sodium (Na+) and potassium (K+), play an important role in neuronal function. Separation of charges is set up—greater concentration of Na+ outside the cell; opposite true for K+. Two forces are set up—electrical and diffusive—to produce the resting membrane potential (about -70 mV, inside negative). 43 An Equilibrium Between Diffusion and Charge Forces Potassium (K+) ions : membrane is highly permeable to them, so they are free to move across it They are attracted to the negative charge inside cell, so will have a higher concentration there. However, diffusion pushes them outside cell where their concentration is lower At equilibrium, most K+ ends up inside the cell because of the relative sizes of the diffusional and charge forces Sodium (Na+) ions = membrane only weakly permeable They are attracted to the negative charges inside cell. Diffusion also pushes them inside the cell (where the concentration is lower) Because the cell is not very permeable to them, the equilibrium results in most Na+ ending up outside the cell. 44 45 Ion channels and membrane pumps VOLTAGE-GATED Permeability changes form low to high as membrane potential becomes less negative (low permeability at resting potential) Ions flow through selective channels that permit only a certain type of ion to move acros...
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This document was uploaded on 02/16/2014.

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