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Biology: Synaptic Events: Cell-Cell Communication


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About this Lesson

  • Type: Video Tutorial
  • Length: 11:11
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 120 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)

A nerve impulse travels down an axon of a
nerve until it reaches the terminal branches of
the axon. The signal then passes from one
neuron to the next across a synapse to the
dendrite of the next neuron. A synapse is the gap between neurons that facilitates cell signaling. As a depolarization wave reaches the presynaptic terminal, vesicles containing neurotransmitters will fuse with the presynaptic membrane and release neurotransmitters into the synapse. These neurotransmitters will bind to protein receptors in the postsynaptic terminal. Neurotransmitters bound to protein receptors can trigger either inhibitory or excitatory signals. Some drugs function by binding to neurotransmitter receptors. Professor Wolfe covers all the basic and some advanced ways that cells communicate with each other.

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.

About this Author

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Recent Reviews

Cell to Cell communication
~ JBlake

Fairly high level of information taking into consideration that my students are all freshman with a wide range of abilities. Overall a good sense of what happens in a cell in regards to communication. The cocaine reference at the end of the video was a bit uncomfortable. I give it a 3/5, considering most of his stuff is spot on.

Cell to Cell communication
~ JBlake

Fairly high level of information taking into consideration that my students are all freshman with a wide range of abilities. Overall a good sense of what happens in a cell in regards to communication. The cocaine reference at the end of the video was a bit uncomfortable. I give it a 3/5, considering most of his stuff is spot on.

What about those places where neurons meet? What about those cell-cell interactions that we've spoken so much about in so many other systems? Do cells, indeed, interact? Well, you know they do. You know the point is, and the point I've made to you, is that quite often, when neurons meet - not quite often, all the time - there's a gap, and that gap is called the synapse, and the synapse is a way to convey an impulse across a space, a fluid filled space. What's going to happen is we are going to have - let me set up some vocabulary for you here - something called the presynaptic membrane and the postsynaptic membrane. I'm just giving this to you in terms of when we talk about it, we know what we're saying.
The postsynaptic membrane simply means this - if you imagine that an impulse is traveling along a neuron, in that direction, and it gets to the terminal branches, and the terminal branches - and I'm going to greatly exaggerate this - over on this side are the dendrites of another neuron and those dendrites will be coming like this, and there will be a gap there. The impulse must somehow get from here to here, and here to here, and here to here. How is going to do that? Well, obviously if this is a fluid filled gap, we must have some kind of rapid diffusion of chemicals. How rapid? Try this. Touch your desk. Ready? How much time did that take to go up your arm, synapse with an interneuron, go up to your brain, process through a bunch of neurons in your brain, say "temperature, pressure," send it back down, synapse with an interneuron, go across, back to that, and say "hard object, not real cold, not real hot." That's kind of cool. That's pretty fast.
So the point is that that's got to be a fairly rapid diffusion. So, we're going to talk about this as being the presynaptic membrane and this is the postsynaptic membrane. That being said, let's take a look at how synapses work.
Here we are at a slightly better diagram than mine, that is going to show - here's the presynaptic membrane and here's the postsynaptic membrane. So, greatly enlarged, this is the tippy-tip of a terminal branch, of a synaptic branch. And what we have is the impulse marked by this arrow coming down. Well, the first thing that's going to happen when we get down to the synapse and the synapse is this space right in here, that I'm drawing in now. That's the synapse. The space between the neurons. What's going to happen first is, as the depolarization wave comes down here, it's going to trigger a membrane change and the action potential when it arrives at the presynaptic membrane, is going to trigger a calcium influx, so calcium ions are going to go shooting in there. In other words, you get another membrane change and the membrane becomes permeable to calcium and it goes shooting in there.
Remember that nerve cells are cells and therefore, they have vesicles, they have Golgi apparatus, they have ER, they have proteins in these vesicles and they have components in these vesicles and there are going to have chemicals within these vesicles called neurotransmitters. So within these vesicles, obviously of Golgi origin, because that where all vesicles pretty much come from, are going to be neurotransmitters. Neurotransmitters can be a variety of different things. In previous lectures, we've mentioned one called acetylcholine. One I want to tell you about maybe later is one called endorphins. They're kind of cool. So, there's a lot of different neurotransmitters.
The key is, here's what the neurotransmitters do. They transmit the impulse and what they do is as soon as the calcium ions come in here, that allows these vesicles to fuse and perform exocytosis, the release of the neurotransmitter - see how everything in this course just builds and builds and builds - you know about exocytosis, and if you don't, you can link back to it. But what's going to happen is the neurotransmitters are going to come across and here comes membrane protein, still again, and sitting here on the membrane of the postsynaptic membrane, are proteins.
Now, let's take a look at what those proteins may look like. Something like this. It's very simple. Just combine what you know about biochemistry. When the neurotransmitter lands on the membrane protein, which is a neurotransmitter receptor - so the protein has a neurotransmitter receptor on it - the protein changes its shape, or the protein channel changes its shape, and materials can go through. And then, the neurotransmitters, which pretty rapidly degrade, the protein shuts up, and what happens? When that opens up, what do you think is going to - you see I've got these things rushing in there? What do you think is going to rush in there to start a depolarization wave? Well, think back to the action potential. What rushed in to start the action potential? You got it. Sodium. Sodium is going to rush in there from the synapse itself. It's going to go pouring in there, starting a new depolarization wave. Amazing. Now, the amazing thing is sometimes these channels are sometimes, depending on the nerve and the whole scenario - and I just have to mention this to you - some will inhibit rather than start an action potential. Remember acetylcholine, in a skeletal muscle it causes contraction. And yet, in a cardiac muscle, it causes relaxation. And, in fact, in that situation, we might get just the opposite effect and we might get a - remember the graph for an action potential, we went from a minus seventy and we skied? Well, in this one, look what happens. In a case where there is an inhibitory response, ions can rush in there that might inhibit. Well, what's going to determine that? The environment of the muscle. The environment of the tissue. What rushes in there or what rushes out - some things might rush out. So, all of this becomes a very complex picture that - take a great neurobiology course and they'll take you through every different tissue and exactly what ions rush in and what ions rush out and how the membranes change. That's exciting stuff. But it's certainly not within the scope of this course.
But here's something I want to tell you about - endorphins. Why do drugs work? Why does something like an opiate affect your brain? It's got to have something to do with neurons. It turns out that there are a group of naturally occurring opiate-like neurotransmitters, called endorphins. They are naturally pain killers and they're produced, obviously, to suppress pain, and pain is a good thing. But pain is a good thing to protect you. We've been through that already. On the other hand, too much pain can really eliminate your survival, because if you're like so involved in the pain, you may miss fighting the lion that's trying to eat you. So, the point is that these are natural pain killers and guess what? It turns out that many plants produce a chemical similar to endorphins. So similar, in fact, that they bind to the neurotransmitter receptor sites, where endorphins would normally bind. So they go to that portion of your brain where endorphins would normally bind and they bind there. And therefore, you get the same effects that you would from an endorphin, just greatly magnified. There's a scary thing about this. There's some drugs we're really worried about. We worry about something like cocaine and we're not exactly sure of how cocaine exactly works, but there is a theory out there that is frightening. Why is it frightening?
Here's why it's frightening. Imagine that this is the cell membrane of a part of your brain called the pleasure center. There are parts in the center of your brain called the pleasure center. Imagine that the pleasure center has neurotransmitter receptor sites to pick up things that make you feel good. So anything that gives you pleasure, is biochemical, and whatever it is, it somehow triggers the release of a chemical that's going to trigger that, and therefore, the nerve you interpret as "Wow, that feels great." We are worried that cocaine goes to the pleasure center of your brain and way overstimulates the pleasure center to the point where there is more cocaine than whatever receptors were there, so the brain may build more of these receptors. The cells may build more of these receptors.
Well, why is that bad? Well what does that mean? That means the next time you take cocaine, you have more receptors. You're going to need more than you did the first time. And then you'll build more and you'll need more than you did the other time. Well, that's called an addiction and if that isn't scary enough, let's make it scarier still. Suppose you stop taking cocaine. Now, you have all these receptor sites on your pleasure center, and what used to give you pleasure, when you only had those, and I'm not talking about cocaine now, I'm talking about regular pleasure things. You may - to experience the same pleasure - never experience it again. That's a scary thought. That's a very biochemically scary thought when it comes to the way neurotransmitters may work.
Animal Systems and Homeostasis
The Nerve Impulse
Human Regulation: Synaptic Events: Cell-Cell Communication Page [1 of 2]

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