"Scott Seidman" wrote in message
. 1.4...
"Wolfgang" wrote in news:5s5gs2F153pe0U1
@mid.individual.net:


"Tom Nakashima" wrote in message
...

Man doesn't lose equilibrium in water.

Not true.

Wolfgang



Correct. The semicircular canals have no problem, but the otolith organs
get confused because there is a bouyancy in addition to gravity. How
this manifests is interesting, but the bottom line is that a diver can
become very disoriented in water, enough that the most reliable way of
telling "which way is up" is to follow your air bubbles.

It's much like microgravity during space travel. Oddly, divers don't get
microgravity sickness like 50% of the astronauts, but that might have
something to do with the lenght of exposure.

One of the things that really gets astronauts hurling is odd visual cues.
Some of the compartments on the space station and shuttle, for example,
have different "up" directions, simply because thats how the things were
built. Walking (or floating) from a room with one orientation to the
next with different orientation could very well be the trigger for the
ride on the porcelain bus.

Underwater, though, I suppose visual cues can be very limited, and this
might contribute to disorientation.

It does. In addition, there are many other cues (besides the vestibular
system and vision) that we normally use to determine orientation and
maintain equilibrium. For one thing, there's simple upright posture. When
horizontal, the human default condition is motionless. Most people don't
have much trouble adjusting to such acitivities as swimming, for example,
but some folks never can manage to overcome disorientation whenever moving
while horizontal. While the vestibular system and visual cues are certainly
involved here (usually) the kinesthetic sense is also crucially important.
Your arms naturally hang "down." There is pressure on the bottoms of the
feet. The head is balanced atop the neck. These are merely some of the
more obvious cues. Others are much more subtle.....so much so that one
never notices them on a conscious level. Hold your arm out and relax the
muscles in your forearm....the wrist bends downward. Easily felt when you
pay attention. But put your hand on a table (palm up or down....it doesn't
matter) and relax. Can you feel the effects of gravity pulling the fingers
down? Probably not. But the brain knows.

I don't know why fish go into some sort of paralytic state when held
upside down, but it might be vestibular.

They don't always. For some fish, being upside down is a normal condition.
Think, remoras, for example. Even in the context under consideration here,
they don't always go limp when held upside down. As for what causes them to
do so when they do, it doesn't seem likely to me that its a function of the
vestibular system. Remember that this particular system is well insulated
from outside influences by being contained within the head, and just about
any fish must often find itself in other than an upright orientation.
Other factors would apopear to be more likely.


Would be very interesting to
find out, anyway.

Yep, and probably not too difficult to devise some simple experiments.

Wolfgang