0:15
I thought you might enjoy a rather whimsical problem session that also has
its important points built in. First let me tell you about a movie of a
giant squid in action. Start your imagination so that you can
watch this movie. So I once went to the Museum of Natural
History in Washington, DC. A museum that's part of the Smithsonian
museums of the United States. And I had been told that there was a movie
there of the giant squid and I wanted to see it.
So I searched and searched and searched and didn't find it.
So I asked one of the people working there.
And they said, oh, you go back into the back corner.
So I'm back into the back corner. And sure enough, there was a machine and a
label that said, Movie of Giant Squid. I had to push the button.
So I've pushed the button. This is where you'll have to use your
imagination. I'm gonna give you a few sketches but use
your imagination here and see this giant squid.
So where the movie was showing was. The movie was not very clear because it
was made way down under water. And it showed this huge thing down there
like that. It was way down underneath the water.
1:44
Just there. And then all of a sudden, all of a sudden,
whoosh. Everything went black.
Well, here it went red. But in the movie, whoosh, everything went
red. Then there was no more squid, it had
disappeared. It's the only movie I ever saw of a giant
squid in action. Now imagine that you are a giant squid.
I know you're not a giant squid, but just imagine that you are.
And suppose you're a squid that wants to be a little better fed.
But to be a little better fed, you have to find more food in a more dangerous
location. So you want to be a little quicker in
escaping from predators. You want to make propagation along the
giant axon, that goes from your head to your tail, go three times as fast.
2:51
And that's a big deal for a giant squid because, as you know from an earlier
segment, giant squids can be as big as a basketball court.
So when they go three times as fast, that's important, because it's got to go
quite a distance. So you decide you want to make your axon
goes three times as fast. That is the action potentials propagate
down the axon, down the axon three times as fast.
Now you're a squid that doesn't really have any ability to change the axon
membrane itself, nor the material outside, nor the material inside, but you can
change, you can because you're a special squid, you can change your giant axon's
diameter. How should you change it?
3:40
Should you make it bigger or smaller. You want it to go three times as fast.
You can make an argument for bigger to say bigger is better and it would go faster.
You can make an argument for smaller that says well, if they're small, it's less to
get excited and so it can do it more quickly.
Which is right? Which one of these changes.
Is necessary. Well, maybe it's something else too.
Well, I bet you get that because you remember an earlier segment, where exactly
this problem was discussed. Choose the right one.
Please fill it in and respond to this question.
5:03
Well of course you can say, this is not really for us to decide.
Squids or mother nature or the evolutionary process, however you would
like to think about it, squids decide what squids should be, not us.
However you would say, that thinking about the way the squid works, there has to be a
balance, some kind of a balance between the electrical funtion.
5:35
Which is what we're talking about propagating action potentials from one
place to another, so as to carry information.
There has to be a balance between the electrical function and the mechanical
function. If you think about the mechanical function
just in the most elementary sense. You'd say, look, this nerve has to fit in
there with all the other body parts. So it can't be too big or it'd squeeze out
everything else. So if it got bigger to go faster and it
got bigger more to go faster yet. Eventually it would be so big that it
couldn't fit in the squid anymore in relation to the other internal organs.
Or if it got smaller to go faster. Oh, very, very small indeed.
Maybe it would no longer be strong enough. It would be so tiny.
And it couldn't, couldn't have the durability this required to live out the
squid, squid's lifetime. I think that this balance has to be
important point in the design of the exon, or at least in the comparison of what
works and what, doesn't work. The electrical function.
In the mechanical function. Also, with respect to electrical function.
Of course, the speed of response is very important.
But the transmission of information is not the only factor determining the speed of
response. There's also squid cognition, whatever
that is, to recognize a danger and respond to it.
That takes some time. I hope not much, but it does take some.
Then there's transmission, but then there's also the operation of the escape
mechanism. The release of all that.
Camouflage ink and the movement of the tentacles in order to propel it away.
Something has to happen there, And squids are wonderful, amazing
creatures. But they have more than one part.
And so the timing required of one part, reducing that may not be too significant
unless you can make the other parts go faster too.
Well I really don't know. But I think it's worth thinking about and
an interesting thing to do. Maybe you can look over the river here and
work that out in your mind. Thank you for watching.
We'll see you in the review session, next time.
Dr. Roger BarrAnderson-Rupp Professor of Biomedical Engineering and Associate Professor of Pediatrics
