Copyright © Philip M. Parker, INSEAD. Terms of Use.
Definition: Action Potential |
Action PotentialNoun1. The local voltage change across the cell wall as a nerve impulse is transmitted. Source: WordNet 1.7.1 Copyright © 2001 by Princeton University. All rights reserved. |
| Domain | Definitions |
Computing | Rapid voltage increase of about 1-ms duration which initiates near the cell soma and propagates along the axon, activating synapses. Source: European Union. (references) |
Medicine | . . the greater the sound pressure, the greater. . . will be the cochlear microphonic and the higher the frequency of discharge of -- in any appropriate nerve fibre. Source: European Union. (references) |
| Potential triggered by depolarization of the membrane from a resting potential of approximately-90 mV to a threshold potential of approximately-70 to-60 mV. Upon reaching the threshold potential, specialized membrane-bound protein channels change conformation from an inactive to an active state, allowing the free influx of Na+ ions into the myocyte and thus determining the upstroke of the action potential(phase 0). The transmembrane potential rapidly changes from-90 mV to approximately +20 mV(hyperpolarization). Shortly after the cell enters the plateau phase(phase 2), during which the cell becomes refractory to further electrical stimulation. Repolarization(phase 3)slowly follows, to be completed when the transmembrane potential regains its resting value of-90 mV(phase 4). Source: European Union. (references) | |
| The electrical effect observed in a muscle or nerve during activity. Source: European Union. (references) | |
Source: compiled by the editor from various references; see credits. | |
(From Wikipedia, the free Encyclopedia)
When a biological cell or patch of membrane undergoes an action potential--or "electrical excitation"--the polarity of the transmembrane voltage swings rapidly from negative to positive and back. Within any one "excitable" cell, consecutive action potentials typically are indistinguishable. Also between different cells the amplitudes of the voltage swings tend to be roughly the same. But the speed and simplicity of action potentials vary significantly between cells, in particular between different cell types.
Minimally, an action potential involves a depolarization, a repolarization and finally a hyperpolarization (or "undershoot"). In specialized muscle cells of the heart, such as the pacemaker cells, a "plateau phase" of intermediate voltage may precede repolarization.
The transmembrane voltage changes that take place during an action potential result from changes in the permeability of the membrane to specific ions, the internal and external concentrations of which cells maintain in an imbalance. In the axon fibers of nerves, depolarization results from the inward rush of sodium ions, while repolarization and hyperpolarization arise from an outward rush of potassium ions. Calcium ions make up most or all of the depolarizing currents at an axon's pre-synaptic terminus, in muscle cells (including the heart's) and in some dendrites.
The imbalance of ions that makes possible not only action potentials but the resting cell potential arises through the work of pumps, in particular the sodium-potassium exchanger.
Changes in membrane permeability and the onset and cessation of ionic currents reflect the opening and closing of "voltage-gated" ion channels, which provide portals through the membrane for ions. Residing in and spanning the membrane, these enzymes sense and respond to changes in transmembrane potential.
Action potentials are triggered by an initial depolarization to the point of threshold. This threshold potential varies but generally is about 15 millivolts above the resting potential of the cell. Typically action potential initiation occurs at a synapse, but may occur anywhere along the axon. In his discovery of "animal electricity," Luigi Galvani elicited an action potential through contact of his scalpel with the sciatic motor nerve of a frog he was dissecting, causing one of its legs to kick as in life.
In the fine fibers of simple (or "unmyelinated) axons, action potentials propagate as waves, which travel at speeds up to 120 meters per second.
The propagation speed of these "impulses" is faster in fatter fibers than in thin ones, other things being equal. In their Nobel prize-winning work uncovering the wave nature and ionic mechanism of action potentials, Alan Hodgkin and Andrew Huxley performed experiments on the "giant fiber" of Atlantic squid. Responsible for initiating flight, this axon is fat enough to be seen without a microscope (100 to 1000 times larger than is typical). This is assumed to reflect an adaptation for speed. Indeed, the velocity of nerve impulses in these fibers is among the fastest in nature.
Many neurons have insulating sheaths of "myelin" surrounding their axons, which enable action potentials to travel faster than in unmyelinated axons of the same diameter. The myelin sheathing normally runs along the axon in sections about 1 mm long, punctuated by unsheathed nodes of Ranvier.
Because the salty cytoplasm of the axon is electrically conductive, and because the myelin inhibits charge leakage through the membrane, depolarization at one node is sufficient to elevate the voltage at a neighboring node to the threshold for action potential initiation. Thus in myelinated axons, action potentials do not propagate as waves, but recur at successive nodes and in effect hop along the axon. This mode of propagation is known as saltatory conduction.
The disease multiple sclerosis (MS) is due to a breakdown of myelin sheathing, and degrades muscle control by destroying axons' ability to conduct action potentials.
Action potentials are measured with the recording techniques of electrophysiology. In the case of an archetypal nerve action potential on an oscilloscope, the relatively large swing to a more positive value, followed by the repolarization recovery and undershoot together trace an arc that could be described as a distorted sine wave--or like the blips on hospital EKG machines that can be seen on TV (these EKG waves are a smear of all the action potentials in one heartbeat, so they enact more slowly than any individual "A.P." and have a somewhat more complicated shape). In an unmyelinated axon that is "firing" an action potential, the transmembrane potential at any instant will vary from point to point along the fiber, with its amplitude depending on whether the A.P. wave has reached that point or passed it, and how long ago. A recording from a single point will show the various stages of the action potential enacted--depolarization, repolarization, hyperpolarization--as the wave passes. Basic Features
Underlying Mechanism
Initiation
Wave Propagation
"Saltatory" propagation
Detection and Observation
Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Action potential."
Crosswords: Action Potential |
| English words defined with "action potential": active ♦ defence, defense, defensive measure ♦ facilitation. (references) |
| Specialty definitions using "action potential": Anti-Arrhythmia Agents, automaticity ♦ electromotive power, Emergency Action Plan, excitatory signal ♦ inhibitory signal ♦ Phototransduction ♦ REAL-ESTATE AGENT ♦ Sanctions, Sodium Channels, stray current. (references) |
| Subject | Topic | Quote |
Health | Repetitive stimulation of a nerve during a nerve conduction study may demonstrate decrements of the muscle action potential due to impaired nerve-to-muscle transmission. (references) | |
Source: compiled by the editor from ICON Group International, Inc.; see credits. | ||
| The following statistics estimate the number of searches per day across the major English-language search engines as identified by various trade publications. Hyperlinks lead to commercial use of the expression at Amazon.com. |
| Expression | Frequency per Day |
action potential | 44 |
cardiac action potential | 6 |
| Source: compiled by the editor from various references; see credits. | |
| Language | Translations for "action potential"; alternative meanings/domain in parentheses. | ||||||||||||||||||||||
Danish | aktionspotentiale. (various references) | ||||||||||||||||||||||
Dutch | actiepotentiaal (spike). (various references) | ||||||||||||||||||||||
Finnish | aktiopotentiaali (spike). (various references) | ||||||||||||||||||||||
French | potentiel de pointe, potentiel de l'action, potentiel d'action. (various references) | ||||||||||||||||||||||
German | Aktionspotential, Erregungspotential. (various references) | ||||||||||||||||||||||
Greek | δυναμικό πράξης, δυναμικό ενέργειας. (various references) | ||||||||||||||||||||||
Italian | potenziale di azione, potenziale d'azione. (various references) | ||||||||||||||||||||||
Pig Latin | actionay otentialpay potencial de acção. (various references) potencial de acción. (various references) aktionspotential, nervimpuls (spike). (various references) | ||||||||||||||||||||||
Scrabble® Enable2K-Verified Anagrams | |
| Words within the letters "a-a-c-e-i-i-l-n-n-o-o-p-t-t-t" | |
-3 letters: placentation, potentiation. | |
-4 letters: attentional, pectination. | |
-5 letters: actinolite, alienation, anticipant, anticipate, antilepton, antipoetic, antipolice, capitation, catenation, citational, coaptation, cottontail, etiolation, noncapital, notational, patination, pentatonic, plantation. | |
| Words containing the letters "a-a-c-e-i-i-l-n-n-o-o-p-t-t-t" | |
+5 letters: compartmentalization. | |
| Source: compiled by the editor from various references; see credits. SCRABBLE® is a registered trademark. All intellectual property rights in and to the game are owned in the U.S.A and Canada by Hasbro Inc., and throughout the rest of the world by J.W. Spear & Sons Limited of Maidenhead, Berkshire, England, a subsidiary of Mattel Inc. Mattel and Spear are not affiliated with Hasbro. | |
Hexadecimal (or equivalents, 770AD-1900s) (references)41 63 74 69 6F 6E 50 6F 74 65 6E 74 69 61 6C |
| Leonardo da Vinci (1452-1519; backwards) (references)
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Binary Code (1918-1938, probably earlier) (references)01000001 01100011 01110100 01101001 01101111 01101110 00100000 01010000 01101111 01110100 01100101 01101110 01110100 01101001 01100001 01101100 |
HTML Code (1990) (references)A c t i o n   P o t e n t i a l |
ISO 10646 (1991-1993) (references)0041 0063 0074 0069 006F 006E 0050 006F 0074 0065 006E 0074 0069 0061 006C |
Encryption (beginner's substitution cypher): (references)3569867581802508186718086756778 |
| 1. Definition 2. Crosswords 3. Quotations: Non-fiction 4. Expressions: Internet | 5. Translations: Modern 6. Anagrams 7. Orthography 8. Bibliography |
Copyright © Philip M. Parker, INSEAD. Terms of Use.
