Talk:Action potential

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" An action potential is an electrical pulse that changes the voltage (potential) across a cell membrane. In

               muscle and nerve cells, this rapid change in voltage leads to an action such as muscular contraction or
               neurotransmitter release. These actions are usually a consequence of calcium ions entering the cell
               during the rapid change in voltage. "

I think any definition has to include the idea of propagation, if not the idea of a wave, which is the mode of propagation in the first kind of action potential most people think of, which is in nerves. It's just wrong that calcium "usually" causes an AP. According to the Hodgkin-Huxley theory, based on the way things work in the giant axon of the squid, all you need are sodium channels and potassium channels. Calcium is important in coupling excitation (the AP) to contraction in muscle, but at the neuromuscular junction its acetylcholine receptors that initiate the action potential, and these will predominantly be carrying sodium into the cell. I suspect they don't permit calcium at all.

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Picture

What does the cartoon of the phospholipid membrane have to do with an action potential? There aren't even any ion channels in the drawing, as far as I could tell. Could someone find a nice graph of an action potential (i.e. a voltage-time graph showing membrane potential increasing to threshold, then firing, then a refractory period)?Sayeth 19:52, Jul 29, 2004 (UTC)

I agree the top picture should be a voltage-time graph. Perhaps when one is found the membrane image could move further down the article? Richard Taylor

Thanks for the new caption, Richard. It makes the drawing much more relevant, but I agree that there's still some improvement possible with a second picture.Sayeth 19:52, Jul 29, 2004 (UTC)

The membrane was uploaded by me in search of a good image for the article, since it was listed as missing an image on Wikipedia talk:Featured article candidates. Apologies if it is only loosely related, and thanks for improving the caption, Richard. Following a request on Wikipedia:Requested pictures, I have created another image from scratch with the voltage, based on images found online at other locations. Hopefully this is more what you had in mind. (I am not very familiar with the topic) Happy editing -- Chris 73 | Talk 08:19, 30 Jul 2004 (UTC)

Thanks, Chris. It looks great. Sayeth 14:02, Jul 30, 2004 (UTC)

I had a few minutes of spare time and decided to redraw Chris' image in Adobe Illustrator. It's basically the same image with some antialiasing and smaller font sizes for readability. Would anyone object if I replaced the current image with my version? --Diberri | Talk 17:22, Jul 30, 2004 (UTC)

Nevermind my asking for permission. I decided to be bold and make the change. --Diberri | Talk 17:49, Jul 30, 2004 (UTC)

Fine with me. The new pic looks good.Sayeth

No problems. Looks good, too. -- Chris 73 | Talk 00:29, 31 Jul 2004 (UTC)

Is the refractory period a) that long and b) is the hyperpolarisation so "hyper" (ie does it go so negative?). I thougth that both were smaller. Batmanand 14:16, 22 Jun 2005 (UTC)

I agree the hyperpolarisation should not be that hyper. Somewhere between 10 and 15 mv would be more accurate. As far as the duration is concerned i think it should be longer, at least 4 ms. David D. 15:13, 22 Jun 2005 (UTC)

I'll add that for the refractory period any time from 1 -15 ms is technically correct since it does vary depending on physiological or developmental context.

Lack of references

Hi this article no longer meets the criteria for a featured article because it does not cite its sources. Please help fix this so that all featured articles can meet the same standards. Best would be the most trusted resources in the field being added, some print resources especially, but also online references are better than none. Those sources would likely help with good material to further improve the article anyway. - Taxman 23:00, Oct 26, 2004 (UTC)

I added two of the most common neuroscience textbooks (Kandel and Bear) as references. If anyone who contributed to this article had more specific references in mind, please add them. Sayeth 17:42, Nov 1, 2004 (UTC)

Would you say you are very confident that the material in those books agrees with what is here? Otherwise that is potentially dishonest to list them as references. - Taxman 19:12, Nov 1, 2004 (UTC)

See discussion on Talk:Synapse.

Correct statements?

The first paragraph reads:

"They [AP's] set the pace of thought and action, constrain the sizes of evolving anatomies and enable centralized control and coordination of organs and tissues. Non-propagating action potentials occur also in some plants."

What is the evidence that the speed of an action potential contrains the size of an organism or organ? It is not discussed in the article.

Also, there are propagating action potentials in plants. They can move along the phloem cell membranes similar to nerves. A good example of this is the sensitive mimosa plant. It's leaflets close in response to touch and the movement can be seen to propagate down the stem. This is due to motor cells sequentially releasing water due to the change in membrane potential as the action potential progress' down the stem. This was observed and published by Charles Darwin in his less famous book The power of movement in plants (http://charles-darwin.classic-literature.co.uk/the-power-of-movement-in-plants/). John Murray, London, 1880. There are two big differences between plant and animal action potentials: 1) plant AP's are much slower; 2) plant AP's are generated with K+ and anions, unlike animals that use K+ and Na+ ions. David D. 15:32, 3 May 2005 (UTC)

"constrain the sizes of evolving anatomies" Maybe there could be a section in the article that cites some references for research dealing with evolutionary constraints that involve action potential generation and propagation. Some textbooks contain statements about the large amount of energy required to support neuronal electrical activity. Some neurobiology texts discuss constraints on brain shape and size that are related to the speed of action potential propagation and how axon diameter and myelination contribute to that velocity. Some people have speculated about the possibility that large animals might be constrained in their body size by the speed of action potential propagation. Memenen 02:12, 6 May 2005 (UTC)