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Biology: Nervous System: Phylogenetic Perspective


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About this Lesson

  • Type: Video Tutorial
  • Length: 8:22
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 89 MB
  • Posted: 07/01/2009

This lesson is part of the following series:

Biology Course (390 lessons, $198.00)
Biology: Animal Systems and Homeostasis (63 lessons, $84.15)
Biology: The Nerve Impulse (6 lessons, $11.88)

Taught by Professor George Wolfe, this lesson was selected from a broader, comprehensive course, Biology. This course and others are available from Thinkwell, Inc. The full course can be found at The full course covers evolution, ecology, inorganic and organic chemistry, cell biology, respiration, molecular genetics, photosynthesis, biotechnology, cell reproduction, Mendelian genetics and mutation, population genetics and mutation, animal systems and homeostasis, evolution of life on earth, and plant systems and homeostasis.

George Wolfe brings 30+ years of teaching and curriculum writing experience to Thinkwell Biology. His teaching career started in Zaire, Africa where he taught Biology, Chemistry, Political Economics, and Physical Education in the Peace Corps. Since then, he's taught in the Western NY region, spending the last 20 years in the Rochester City School District where he is the Director of the Loudoun Academy of Science. Besides his teaching career, Mr. Wolfe has also been an Emmy-winning television host, fielding live questions for the PBS/WXXI production of Homework Hotline as well as writing and performing in "Football Physics" segments for the Buffalo Bills and the Discover Channel. His contributions to education have been extensive, serving on multiple advisory boards including the Cornell Institute of Physics Teachers, the Cornell Institute of Biology Teachers and the Harvard-Smithsonian Center for Astrophysics SportSmarts curriculum project. He has authored several publications including "The Nasonia Project", a lab series built around the genetics and behaviors of a parasitic wasp. He has received numerous awards throughout his teaching career including the NSTA Presidential Excellence Award, The National Association of Biology Teachers Outstanding Biology Teacher Award for New York State, The Shell Award for Outstanding Science Educator, and was recently inducted in the National Teaching Hall of Fame.

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I'm gonna make a confession to you guys. But don't tell too many people about this. I'm going to tell you about one of my favorite movies of all time, and if they were going to make a Broadway show of this movie, and they asked me to be in it, I would give up my life to do this. And it's the Wizard of Oz. And my favorite character in the Wizard of Oz is the Scarecrow. And I can just see myself standing there dancing--I can't dance, you probably could figure that out--but you know, that whole song "If I only had a brain." That's my first confession. My second confession is that I'd like to make a movie, and in this movie I would feature that song, and it would be like a biologist's view of the Wizard of Oz. And I would pick different creatures to play the different parts. And you know who I would pick to sing "If I only had a brain"? There's really not that many creatures I could use for that part, but the guys I would pick would be the jellyfish or the hydras of the sea anemones because they don't have brains. Can't you just see the little hydras..."if I only had a brain." Because they don't have brains! And they don't have brains for evolutionary reasons. Let's talk Biology here.
Let's talk about evolutionary history. You know, we've been through a lot of systems together, you and I, as we've grown up through Biology, and one of the things that you've seen is the dilemma that multi-cellularity has brought to life on this planet. It's great to be multi-cellular, once again, but there have been dilemmas. And the dilemmas have been homeostatic regulation. I think you've heard that term before. And, you know, how do we get gases? How do we transport gases? How do we exchange gases? How do we do all these different things; heart rate, and information processing, etc. But we came up with these systems and we're happy because of this, but the last piece of the puzzle is: How do you get one system to communicate with the other? And how do you get the digestive system to communicate with the transport system? How do you get the transport system to communicate with the endocrine system? How do you do communication? Whether you are a worm, or whether you are a fish, or whether you are you. How does this communication occur?
Well, that's a darn good question, and one we probably ought to address. Now, when you're cells, that's easy. Cells can communicate. You remember ion channels, we have these junctions where ions can pass through, you know that there are receptors on the cell membrane just sitting out there waiting to grab things like hormones that float by. But as complexity increases and you go from the cellular level and the tissue level to the organ level and the system level, it gets a lot more important to communicate and communicate quickly. And somewhere along the line, there was some very, very clever adaptations made that allowed communication. Now let's not look at this in a Lamarckian sense, it's not like one day there was this multi-organ critter and it said "I need to communicate within systems. I think I'll evolve nerve cells." No, that's not what we're talking about here. But from a situation where there was no communication at all to one where cells had specialized adaptations where a signal can be sent, we eventually came up with things called nervous systems.
I want to go back phylogenetically to the very first animals and talk about their nervous systems. Ready? What's the most primitive, the most ancient animal you can think of? Did you say sponge? You're absolutely right. Now tell me what you know about their nervous systems. Not much, because there are none. You see, sponges, and if you look at the phylogeny of sponges, they're practically colonial. They do have specialized cells, but there is literally no neurology to a sponge. They don't talk to each other, the cells. Sponges are pretty disorganized. The very first creatures were those singing hydras and jellyfish. Why? Because, what you know about hydras, and what you know about jellyfish, and what you know about sea anemones, which are basically upside down jellyfish with their tentacles pointed up, is the fact that they are two cell layers thick, but in between those two cell layers is a network of--very primitive--but, nevertheless, they are a network of very primitive nerve cells and these Cnidarians, the whole group, the whole phyla are called Cnidaria with their two cell layers thick. They have no brain, thus they're singing that song, but they do have this network, and therefore sensory impulses can be transmitted so that when some unsuspecting little creature swims by this sea anemone, and he stings it, he can then suck it into his gut and secrete digestive juices. Again, a very simple creature, two cell layers thick with a network of nerves, they're multi-directional, it goes all over the thing. There are very primitive receptors. But we're not talking about something that's going to be going to Harvard here.
Well, as evolution continued and organisms closed up, if you will, something very important happened. And you look back at those phylogeny lectures, and you're going to see a term called cephalization, the formation of a head. It's the only way to get ahead in life. And what happened once we got to cephalization--this had huge ramifications in terms of digestion, in terms of transport, but it really had ramifications in terms of nervous control. Because now--and this is about as primitive as you can get after jellyfish, Platyhelminthes, flatworms; to all you flatworms out there, I'm sorry I don't mean to insult you, but I have read that you can train these things, so maybe they're not as dumb as I'm making them sound. I personally have trained a worm, but not a flatworm. I've trained a marine worm, and I didn't train to be like an attack worm or anything, I trained it to just respond to stimuli when I was an undergraduate. I only got a C on that project, and I don't know why. But anyway, this thing has clusters of nerves and connected to that are side nerves--I don't want to call them peripheral nerves, peripheral neurons, side neurons--but the key here is a collection of neurons in the head, to the point where we could almost call it a brain. Now, at this level, is it called a brain or a collection of brains called a ganglion, and some people will call this a brain because at this point, we're in a gray area. I know some people who I think only have ganglia in their heads, but we won't talk about them. Nevertheless, that's the collection of brain.
As cephalization continued and things continued to advance, what started to happen was the ganglia started to talk to each other and the ganglia collected, and there were more and more and more ganglia, and eventually came along a centralized nervous system. Now, obviously I'm holding humans up here, but there are other things with brains on the planet too: earthworms, marine worms, mollusks, starfish, squid, clams. In fact, just about everything but jellyfish has a brain! So you can start to see that this whole idea of concentrating ganglia to form a brain and a way to connect that brain to the rest of the body--in our case, a spinal cord--and peripheral materials, peripheral neurons to send them out to the body became a major evolutionary advance that allowed homeostasis to take off. We'll see more about these brains later on.
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The Nervous System: A Phylogenetic Perspective Page [1 of 2]

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