Hyperpolarization (biology)
You don't need to be Editor-In-Chief to add or edit content to WikiDoc. You can begin to add to or edit text on this WikiDoc page by clicking on the edit button at the top of this page. Next enter or edit the information that you would like to appear here. Once you are done editing, scroll down and click the Save page button at the bottom of the page.
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Phone:617-525-6884
Please Take Over This Page and Apply to be Editor-In-Chief for this topic: There can be one or more than one Editor-In-Chief. You may also apply to be an Associate Editor-In-Chief of one of the subtopics below. Please mail us [2] to indicate your interest in serving either as an Editor-In-Chief of the entire topic or as an Associate Editor-In-Chief for a subtopic. Please be sure to attach your CV and or biographical sketch.
Hyperpolarization is any change in a cell's membrane potential that makes it more polarized. That is, hyperpolarization is an increase in the absolute value of a cell's membrane potential. Thus, any change of membrane voltage in which the membrane potential moves farther from zero, in either a positive or negative direction, is a hyperpolarization.
Examples
1. During the undershoot period after an action potential, the membrane potential is more negative than when the cell is in the "resting state". In the figure to the right, this undershoot is from approximately 3 to 4 milliseconds (ms) on the graph. The undershoot is the time when the membrane potential is hyperpolarized relative to the resting potential.
2. During the rising phase of an action potential, the membrane potential changes from negative to positive. In the figure, the rising phase is from approximately 1 to 2 milliseconds on the graph. During the rising phase, once the membrane potential becomes positive, the membrane potential continues to hyperpolarize until the peak of the action potential is reached at about +40 millivolts.
In both examples 1 and 2 (above), the hyperpolarization of a biological cell means an increase in the trans-membrane voltage; the membrane charge is more polarized. Thus, hyperpolarizations can be changes in membrane potential that are either in the positive or the negative direction.
In the scientific vernacular however, "hyperpolarization" (and its opposite, "depolarization") are sometimes used in a different way than described above. See the article depolarization for its technical definition and how it is used in descriptions of membrane potential changes. See the next section (below) for hyperpolarization.
Vernacular usage
For the description of action potentials, "hyperpolarization" has taken on an informal, technically incorrect meaning. In this scientific vernacular, hyperpolarization is often used to describe a change in membrane potential that makes it more negative (less positive). However, during the falling phase of the action potential (approximately from 2 to 3 milliseconds in the figure) the membrane potential first becomes less positive after the peak of the action potential and approaches zero. Membrane potential changes from +40 to 0 are technically depolarization of the membrane, not hyperpolarization. Despite it being technically incorrect, text books[1] sometimes use "hyperpolarization" to describe membrane potential changes in the direction from positive to negative such as the entire falling phase of the action potential.
References
See also
External links
- Neuroscience - online textbook by Purves, et al
- Basic Neurochemistry Molecular, Cellular, and Medical Aspects by Siegel, et al
de:Hyperpolarisation (Biologie)fi:Hyperpolarisaatio
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
