TOEFL Listening: ETS-TOEFL听力机经 - SWTNZDQ61B531A28Q$

Lecture: Neurons: the communication that goes on within the brain: Narrator: Listen to part of a lecture in a biology class Professor: Ok, So last class we were talking about human brains and neurons, you know nerve cells in the brain. Just a quick review, someone tell me about neurons, how do they work? Bernard? Bernard: They, well, neurons are kind of like wires carrying electrical signals. And when the electrical signals reach a contact point then a message is sent off to another neuron. And I guess an interesting thing about neurons is that ... Professor: Yes, exactly! That's fine Bernard. Today I want to discuss other cells found in the brain. They're called glial cells. Just so you know there are different types of glial cells, but we'll discuss specific types later. Right, glial cells, so, first off, historically speaking, and I'm talking about the 1950s here, researchers didn't think glial cells were that important. They always focused on neurons, neurons, neurons and the thinking was that neurons are responsible for all the communication that goes on within the brain. As far as glial cells were concerned, early researchers thought they just supported these communicating neurons by doing a few jobs like carrying nutrients to neurons because in order to keep functioning brain neurons need energy. And another job is protecting the brain from agents of disease, you know, urn, things that the immune system should have discovered and captured, but didn't. So again, early research assumed that the main purpose of glial cells was to support neurons. That with their support the brain's neurons could do their communicating. With their support, neurons could make the connections that allow us to think, feel, remember or even eat a sandwich. So the thinking was, why study glial cells? These days though, there's new thinking on glial cells. In recent research, we've discovered an exchange of information, communication between the brain's neurons and the glial cells throughout one's lifetime. So instead of glial cells having just a maintenance role, we see them communicating, actually having an impact on the connections of neurons, swaying them, determining which connections grow stronger, which grow weaker. So there are really three communication networks, or communication systems in the brain: Neurons communicating with neurons, glial cells communicating with glial cells and then glial cells communicating with neurons. So, in other words, glial cells do much much more than previously thought. At least , that's what the recent research is showing. And where will this new understanding of cell function lead us?We don't know. It's very exciting. And the really marvel us part is glial cells outnumber neurons in the brain by far. But they've barely been explored ... Wanda, you have a question? Student2: So, the field of research in glial cells is growing? Professor: I think there's a lot of opportunity in glial cells research, especially a few years from now when you folks graduate. As I see it the field is really opening up. But let's go back a little and analyze. Why did we miss so much about glial cells in the past? Well, we had incorrect assumptions about glial cells. We knew how signals traveled through neurons and assumed that glial cells would use the same mainly electrical mode of transmitting information. But they don't. Again, just as you explained, neurons mainly use electrical activity to carry the message. Glial cells, though, glial cells use chemicals not electrical signals to carry messages. And since our basic assumption back then was wrong we missed out on a real understanding. And there's still lots we don't know. What else can glial cells do? Can they repair nerve damage for instance? We're still asking questions, experimenting and learning. Some people have an extremely high number of glial cells, more than normal. More than the typical person's brain has. One question we have: does the higher number of glial cells in the brain mean greater intelligence? And there are different type of glial cells, so maybe being a genius is caused by having an unusually high number of them or maybe just of a certain type. We don't know yet. As we gain answers to these questions what will we be able to do that we couldn't do before? Well perhaps someday we'll be able to utilize glial cells to treat injuries. Some scientists are doing experiments on that possibility now. Student2: But what do you think Doctor Zoller? Professor: Well, I think yeah! Soon we' II be able to accomplish new things in neuroscience and in the field of medicine as we gain a deeper understanding of how the brain works. Does anyone have other questions? No? We'll move on to other types of glial cells then.