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Thread: The purpose of vasovagal syncope

  1. #1 The purpose of vasovagal syncope 
    Moderator Moderator Cogito Ergo Sum's Avatar
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    Some people faint when they see something upsetting (e.g. blood, hypodermic needles). This reaction is called vasovagal syncope and is:
    "a benign and common emotional reaction (...).
    In vasovagal syncope, signals from the nervous system cause a sudden decrease in blood pressure, and the individual faints from lack of oxygen to the brain."


    Although the mechanism behind the fainting is known, I do not understand what the purpose is of fainting due to an upsetting sight.
    Would it not be more logical if the brain decided to run away, in order to avoid the possible danger?

    Can you help me out?


    Source:
    Silverthorn, D.U. (2012), "Human Physiology, 6th Edition", Pearson, p. 509


    "The only safe rule is to dispute only with those of your acquaintance of whom you know that they possess sufficient intelligence and self-respect not to advance absurdities; to appeal to reason and not to authority, and to listen to reason and yield to it; and, finally, to be willing to accept reason even from an opponent, and to be just enough to bear being proved to be in the wrong."

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    Forum Masters Degree LuciDreaming's Avatar
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    There are quite a few mammals who freeze (rodents) or pass out (goats) when they feel threatened - I suppose because there are a lot of prey mammals that wont react unless they detect movement - an echo of that possibly? so that's my wild guess.


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    Genius Duck Dywyddyr's Avatar
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    Possibly: some predators only go after live prey - fainting "makes you dead" you as far as they're concerned.
    "[Dywyddyr] makes a grumpy bastard like me seem like a happy go lucky scamp" - PhDemon
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    Moderator Moderator Cogito Ergo Sum's Avatar
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    Quote Originally Posted by LuciDreaming View Post
    There are quite a few mammals who freeze (rodents) or pass out (goats) when they feel threatened - I suppose because there are a lot of prey mammals that wont react unless they detect movement - an echo of that possibly? so that's my wild guess.

    You postulate that it is a survival mechanism?
    It does not seem far-fetched, because it fits within the theory of evolution; fainting to avoid predators in order to increase your chance to produce fertile descendants.

    Of course, an neurological role can also be a part of the solution. Perhaps it is caused by a different 'wiring' of the (inter)neurons in the brain?
    "The only safe rule is to dispute only with those of your acquaintance of whom you know that they possess sufficient intelligence and self-respect not to advance absurdities; to appeal to reason and not to authority, and to listen to reason and yield to it; and, finally, to be willing to accept reason even from an opponent, and to be just enough to bear being proved to be in the wrong."

    ~ Arthur Schopenhauer, The Art of Being Right: 38 Ways to Win an Argument (1831), Stratagem XXXVIII.
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    Remember, a lot of people extend the self protection responses to fight, flight, freeze rather than simply fight or flight.

    One "useful" version might be that it's an extension or relic of infant responses. Not seen it talked about in humans or other apes, but there are plenty of other animals whose young have that "freeze" response to fear where the mature adults have an aggressive or protective or other non-freezing response. Come to think of it, you do see that freeze response in young apes - to threats from adults or adolescents within their group rather than from outside it.
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    Forum Ph.D.
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    It is interesting that you assume that because something is present that it has a "purpose". That is not a very scientific sort of thing to think.
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    Moderator Moderator Cogito Ergo Sum's Avatar
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    Quote Originally Posted by Sealeaf View Post
    It is interesting that you assume that because something is present that it has a "purpose". That is not a very scientific sort of thing to think.

    In hindsight, I should have asked if this phenomenon has a function and if so, what the function was.
    Some users have stated that fainting/freezing is present in some species and it serves a certain role.

    Yet, I do understand why my assumption is not very scientific.
    "The only safe rule is to dispute only with those of your acquaintance of whom you know that they possess sufficient intelligence and self-respect not to advance absurdities; to appeal to reason and not to authority, and to listen to reason and yield to it; and, finally, to be willing to accept reason even from an opponent, and to be just enough to bear being proved to be in the wrong."

    ~ Arthur Schopenhauer, The Art of Being Right: 38 Ways to Win an Argument (1831), Stratagem XXXVIII.
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  9. #8  
    Forum Professor jrmonroe's Avatar
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    Quote Originally Posted by LuciDreaming View Post
    There are quite a few mammals who freeze (rodents) or pass out (goats) when they feel threatened - I suppose because there are a lot of prey mammals that wont react unless they detect movement - an echo of that possibly? so that's my wild guess.
    Yes, to the two classically-known "F" responses, Fight or Flight, there's also three more — Freeze, Feign and Faint.

    Walking through the woods one day, I didn't realize that I happened upon a young deer (which had been Freezing) until I came within about 5 feet and it suddenly bolted (Flight).

    As for the last two in my list, Feign and Faint, the hognose snake is a good example. If it notices a potential predator nearby and cannot flee (Flight), it will rear up, flatten its head, hiss and maybe even feign to strike (the classic traits of a poisonous snake) even though it is non-poisonous. If Feigning doesn't scare away the predator, then it will drop to the ground, roll onto its back, displaying its white belly, play dead, sh*t itself, stick out its tongue, and smell nasty (Faint). Yet, it continues to watch the predator, and as soon as it looks away, the snake will quickly collect itself and slither away (Flight).
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