Re: Fish don't have ethical feet it doesn't mean they can't move- was Re: Ethical feet


"whisky-dave" <whisky-dave@xxxxxxxxxxxxxxx> wrote in message
news:dbo5dm$5nl$1@xxxxxxxxxxxxxxxxxx
>
> "H Duffy" <Hester_Duffy_nospam@xxxxxxxxxxx> wrote in message
> news:3k7qerFt0gp5U1@xxxxxxxxxxxxxxxxx
>> Actually, no. Some parts of human brains are very different from fish
>> brains, but the bits of brain that we have in common behave in extremely
>> similar ways, down to using the same neurotransmitters such as serotonin
>> and substance P.
>
> "The ability to detect and react to nociceptive stimuli is a widespread
> characteristic of animal life. Single-celled creatures such as an ameba
> will move away from irritating chemical or mechanical stimuli. These
> reactions are automatic and because the ameba doesn't have a nervous
> system, it has no ability to actually sense the stimulus that causes its
> reaction or to feel pain."
>
> Is this evidence that amebas feel pain too ? or is it just baised ?

No, it isn't evidence that amoebas feel pain; they have no nervous systems,
and are therefore unable to feel anything. On the other hand, fish have
sophisticated nervous systems, complete with subsystems which are
specifically designed to feel pain.

>> You mean tissue death, which is slightly different. As cells age and die
>> off, they don't hurt. However, if perfectly healthy tissue (as opposed to
>> individual cells) is damaged, it almost always _does_ cause pain. There
>> are a few cases in which it doesn't, with leprosy being the most obvious,
>> but that's because it kills the nerves first, so when tissue gets
>> damaged, there's nothing there to transmit the pain.
> Pain is not transmitted, signals are

Could you explain to me what you think pain is, if not a signal transmitted
by the nervous system?

>> In normal circumstances, it does. Some chemical block pain signals; that
>> doesn't mean that normally, tissue damage doesn't cause pain; normally,
>> tissue damage _does_ cause pain.
> Only because of what the signals tell the brain to 'feel' .

No, not necessarily; local anaesthetics don't get to the brain; they block
the signals at the site of origin.

> Remember the brain can feel pain in places that don't exist in reality.

Yes, and it can hallucinate images and sounds which don't exist. Does that
mean that everything we see is actually only in our heads and not in the
real world?

>>It's an experiment which has been done to investigate pain and where pain
>>is experienced. Basically, what you do (if you're a qualified
>>neuroscientist; don't do this at home, kids) is you take an adult cat, and
>>you sever the spinal cord at the base of the skull in such a way that you
>>don't actually damage anything vital to life; the cat carries on
>>breathing, its heart still breathes, it can even eat and drink (although
>>usually such animals are tube-fed). What it can't do is move voluntarily,
>>or feel physical sensations below the point of severance.
>> However, if you stab its paw with a pin, it withdraws its paw. Magic,
>> huh?
>
> But is that because of pain ?

Yes; if you stroke the paw, it doesn't withdraw it; it is specifically
painful stimuli which get that reaction.

> try touching the paw with a feather see if that causes the same pain.

it doesn't.

>> Well, no, not magic; what this proves is that pain is experienced in the
>> body, not just the brain, even if it it not experienced consciously (the
>> cat will show no distress at being stabbed with a pin).
>
> You said it retracted it's paw, do you know why it did that.
> Because if you tocuh a cats paw normally it will move it.

Yes, but that's a voluntary reflex, controlled by the brain. In spinal cats,
they don't have any voluntary control over their limbs, because the brain
has been disconnected from the body.

>> Come to think of it, there was a case of a man who had suffered damage to
>> the spinal cord after an accident, and was paraplegic; he had no
>> voluntary control below about the 5th rib, IIRC, and therefore no feeling
>> in his lower torso and legs, and no bowel or bladder control. In order to
>> help him with the latter problems, scientists wired him up, in such a way
>> that they could deliver a small electric shock (which he couldn't
>> consciously feel) to his thigh, and a large electric shock (which again
>> he couldn't consciously feel) to his bladder. This latter shock was
>> strong enough to cause his bladder to contract and thus empty; i.e. when
>> they delivered the strong shock to the bladder, he peed.
>
> Wow so they sent signals to organs to get them to do things.

Yes; that's not the clever bit.

>
>> Over a period of days, they would deliver a small shock to his thigh, adn
>> then immediately afterwards, a strong shock to his bladder, causing him
>> to pee. Aftter a few days, they no longer needed the strong shock to the
>> bladder; the small shock to his thigh was enough on its own to trigger
>> his bladder to empty.
> So he's body learned this did it or was it the brain that learnt this.

The brain couldn't possibly have learnt to do it, given that his brain, like
that of the spinal cat, was no longer properly connected to his lower body;
he had no feeling and no voluntary movement.

>> Bear in mind that he was not consciously aware of any sensation either in
>> his thigh or in his bladder. if the pain was _only_ experienced by his
>> brain, the shock to his thigh could not possibly have triggered anything
>> in his bladder.
>> However, since pain is actually experienced in the non-central nervous
>> system too, his body was able to learn, without intervention from his
>> brain, and thus he was able to regain voluntary control over his bladder.
>
> But what has this to do with pain, kids learn to not pee in their sleep
> due to the brain learnign to control the body nothing to do with parents
> slapping their kids because they wet the bed. The bladdr is not controlled
> by giving it pain but by signals.

Yes, but the signals in this case came from his thigh, not from his brain.
The point is that, although he was not aware of the sensation of the shock
to his thigh, and it didn't register in his brain, it clearly was being
registered by his nervous system. Therefore, it cannot be true that pain is
processed purely by the brain.

>> That's right, yes; it is possible to interrupt the transmission of pain,
> You can't transmit pain, only the signal.

The pain is the signal, the signal is the pain.

>> just as it is possible to create pain without tissue damage, but that
>> doesn't mean that, under normal circumstances, tissue damage doesn't
>> cause pain.
> The association of pain can be because of tissue damage.

The association of pain with what?

H


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