AGRC1020 Lecture Notes - Lecture 2: Electrochemical Gradient, Cell Membrane, Extracellular Fluid
6 Aug 2018
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Document Summary
All cells maintain a voltage across their plasma membranes. Voltage is electrical potential energy due to the separation of opposite charges. The cytoplasm of a cell is negative in charge compared to the extracellular fluid because of an unequal distribution of cations and anions on opposite sides of the membrane. The voltage across a membrane is called a membrane potential, and ranges from 50 to 200 millivolts (mv). The inside of the cell is negative compared to the outside. The membrane potential favors the passive transport of cations into the cell and anions out of the cell. Two combined forces, collectively called the electrochemical gradient, drive the diffusion of ions across a membrane. One is a chemical force based on an ion"s concentration gradient. The other is an electrical force based on the effect of the membrane potential on the ion"s movement. An ion does not simply diffuse down its concentration gradient but diffuses down its electrochemical gradient.
