Very apt phraseology - the leg muscles of frogs have very commonly been used for studying the electrical responses of muscles, and they're amazingly strong.... I took off like a giant frog.
Kind Regards, John.
A Tale of Woe - A Lesson Learnt
- Thread starter Nick98
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Kind Regards, John.
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And prompted early work on electricity itself, as per Luigi Galvani and his associate Alessandro Volta.
Exactly. I think the subsequent widespread use of frog leg muscles for electrophysiological research was probably a perpetuation of what had happened in those very earliest days of electrical discovery.
Kind Regards, John
I think you are both right and both wrong.
It is not so much whether it is DC or AC but where the current flows through the body. DC though a single muscle will make that muscle contract and not relax until the current is removed or the muscle tires.
Take the very simple example ( as demonstrated in school phsyics 1960's) of a DC voltage applied from palm to various points on the fore arm. DC through the muscles that clench the fist and the fist will clench. DC through the muscles that open the fist and the fist will open with pain in the fingers. DC through both and the action is not determinable but the pain as both muscles are pulling against each other ( at up to 7 times normal power ) is enough to make the upper arm muscles act in reflex action to move the lower arm away from the source of pain. Severe pain and more of the body acts to move from the source of pain. Even if the hand is clenched onto the conductor the arm movent is likely to break the other point of contact and remove the current so the muscles will then relax and the clenching released.
The over all effect of an electric shock depends on the route the current takes through the body and which muscles and nerves are affected both directly and by pain reflex indirectly. It is possibly that it is only the pain reflex action that breaks one or both points of contact.
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I did say that it was "a serious simplification of a very complicated situation" but what I posted last night was probably about the closest one can get to a summary of the 'most common bottom line' for voltages in the range 100V-300V. As you say, many factors, particularly 'where the current flows' are important determinants of what happens. One also has to understand that the muscle activity one sees in response to a shock is at least as much due to stimulation of nerves as the muscles themselves.
That's essentially true, but you are probably talking about voltages <100V (for which things are rather different), and 'targetted' electrode placement. The fact remains that, in the real world of electric shocks, with voltages in the 100-300V range it would be unusual to see sustained muscle contraction as a result of a DC current. I could attempt to give you an electrophysiological/ electrochemical explanation, but this forum is probably not the place for that! Of course, in contrast with the situation not many years ago, DC voltages >100V are now rarely encountered by most people, so this discussion about AC vs DC shocks is becoming somewhat academic. In my mispent (and sometimes foolish) youth, most of the 'jolts' I suffered were from DC in the range 200V-1500V, but I'm sure that such incidents are a rarity these days.
One of the ironies is, as I implied in my previous message, that 50Hz is very close to being the 'optimum' frequency of AC for its effects on nerves, muscles and the heart (again, for electrophysiological reason that I could attempt to explain if you wished).
The route of the current is certainly a crucial factor. Pain reflexes are probably less helpful than you might think, because they are generally programmed to work via the muscles in the vicinity of the source of pain - muscles which, in the presence of an ongoing electric shock, are often unable to respond to the 'requests' of the reflex. If reflexes thought a bit more laterally, and caused one's leg muscles to respond to pain due to electric shock in the hand, that might be much more effective! (in fact, that can sometimes happen with severe shocks)
Kind Regards, John.
Then they wouldn't be reflexes.
So much for my attempt to use light-hearted informal language
In fact, perhaps relevent to this discussion, although (as you righly imply) reflexes are essentially automated responses (therefore don't 'think'), many of them can be modulated or inhibited by thought processes (whether conscious or subconcious). The classic textbook example is of the reflex that causes one to immediately drop a very hot plate if one picks it up. If one knows that it's worth thousands of pounds, one can often inhibit that reflex .. and then, of course, to lower the tone, there's the matter of 'house training' (of humans, as well as pets!)
Kind Regards, John.
Yeah.
Well.
I wish, in an episode from my misspent youth, that I could have trained my reflexes not to lunge down and grab something I'd knocked off the bench when that something was a soldering iron which managed to give me 3 lines of burns across my fingers and palm before the next reflex kicked in.....
Well.
I wish, in an episode from my misspent youth, that I could have trained my reflexes not to lunge down and grab something I'd knocked off the bench when that something was a soldering iron which managed to give me 3 lines of burns across my fingers and palm before the next reflex kicked in.....
Definitely agreed - I suffered almost exactly the same fate, more than once!I wish, in an episode from my misspent youth, that I could have trained my reflexes not to lunge down and grab something I'd knocked off the bench when that something was a soldering iron which managed to give me 3 lines of burns across my fingers and palm before the next reflex kicked in.....
Kind Regards, John.
then, of course, to lower the tone, there's the matter of 'house training' (of humans, as well as pets!)
Result of BAS's endevour to have his wicked way with her by plying her with too much drink?
I'm sure that's not BAS's style.....
Yup.
Nothing better than an unconscious woman who's wet herself.
Nothing better than an unconscious woman who's wet herself.
I wonder if having not won her over BAS needs to have one of these fitted to their door.
It would give the lady time to change her mind about leaving.
http://www.artlebedev.com/everything/defendius/
It would give the lady time to change her mind about leaving.
http://www.artlebedev.com/everything/defendius/
Realistically, would a PIR have picked that up ? The tester would need to identify that it was an unused circuit (yup, should manage that), but then would have to guess where the end was and go looking for it to see it it was adequately protected. Unless it was obvious (and in this case it was buried in thermal insulation and so not visible), would he not have to make assumptions ? After all, it could just as easily have been safely terminated in a JB under the floorboards.
Or would you just note on the paperwork that you couldn't find the end, in which case a non-trained recipient of the report would be non the wiser.
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