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    Then why would contracting them for a long time (ie looking at close things and concentrating) gets them tired???

    Anyone not as thick as me and know this (i m sure theres a really simple response, eg ciliary muscles are actually skeletal or something like that)
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    I think it's because the anaerobic respiration required for producing extra ATP also produces lactic acid, which when accumulates, causes fatigue.
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    AFAIK they are striated (skeletal) muscle, but I COULD be wrong.
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    They're smooth and I think endeavor's right.
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    Well, that's a rather generic explanation for why any muscle gets fatigued though :p:

    Tbh I don't know if they ever told us it was smooth or not - I guess if I'd LOOKED in histology rather than trying not to throw up because of my hangover, I might have noticed
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    byt the same token. wouldnt eating a lot (and causing loads of peristalsis) make ur oesophagus etc tired?
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    The only explanation I can come up with is (and its a bit of a guess) that in peristalsis, there are alot of muscles at work and the contraction is in waves. Therefore, each muscle has time to recover between each contraction and so never really tires (like the refractory period in the cardiac cycle allows the cardiac muscle to continually beat). In the eye, however, there are fewer muscles working and they are continually contracting and relaxing. There is rarely a time when our eyes are open which does not require us to alter our focus slightly. This maybe why our eye muscles eventually do tire - because over long periods of time, some lactic acid will build up. Well its a guess, but it sorta holds together.
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    (Original post by ecolier)
    Then why would contracting them for a long time (ie looking at close things and concentrating) gets them tired???

    Anyone not as thick as me and know this (i m sure theres a really simple response, eg ciliary muscles are actually skeletal or something like that)

    I don't see why you think smooth muscle can't "get tired". Repeated stimulation or prolonged contraction of any muscle causes fatigue, regardless of whether there are evident striations. In the case of the near-sighted accomodation, not only does the ciliary musle contract, but the choroid to which it is attached and the zonule fibres are put under tension.
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    Hmm.... maybe the muscles in our intestines do get tired, just that we cannot feel it. I know that in the stomach, the only sensory receptors are pain receptors (--> we cannot feel peristalsis, just stomachache). The question is whether there are receptors sensing "tiredness" (mechanoreceptors?! other types of pain receptors?) in the eyes. :confused:

    Moreover, are you sure tiredness in the eyes is not psychological?! :p:
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    thanx for all the responses, so far we have

    )aerobic respiration causes lactate build-up
    )ciliary muscles are actually skeletal muscles
    )smooth muscles do get tired
    )psycological feeling made up by brain

    any more responses? i want get as many constructive responses as possible, thanx!
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    Ciliary muscles are, according to toyl, not skeletal. I actually don't know any more. I would just say fixed contraction for a long period of time -->anaerobic resp and lactate buildup-->fatigue etc.
 
 
 
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