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  • We could have a debate about what the most interesting cell

  • in the human body is, but I think easily the neuron would

  • make the top five, and it's not just because the cell

  • itself is interesting.

  • The fact that it essentially makes up our brain and our

  • nervous system and is responsible for the thoughts

  • and our feelings and maybe for all of our sentience, I think,

  • would easily make it the top one or two cells.

  • So what I want to do is first to show you what a neuron

  • looks like.

  • And, of course, this is kind of the perfect example.

  • This isn't what all neurons look like.

  • And then we're going to talk a little bit about how it

  • performs its function, which is essentially communication,

  • essentially transmitting signals across its length,

  • depending on the signals it receives.

  • So if I were to draw a neuron-- let me

  • pick a better color.

  • So let's say I have a neuron.

  • It looks something like this.

  • So in the middle you have your soma and then from the soma--

  • let me draw the nucleus.

  • This is a nucleus, just like any cell's nucleus.

  • And then the soma's considered the body of the neuron and

  • then the neuron has these little things sticking out

  • from it that keep branching off.

  • Maybe they look something like this.

  • I don't want to spend too much time just drawing the neuron,

  • but you've probably seen drawings like this before.

  • And these branches off of the soma of the neuron, off of its

  • body, these are called dendrites.

  • They can keep splitting off like that.

  • I want to do a fairly reasonable drawing so I'll

  • spend a little time doing that.

  • So these right here, these are dendrites.

  • And these tend to be-- and nothing is

  • always the case in biology.

  • Sometimes different parts of different cells perform other

  • functions, but these tend to be where the neuron receives

  • its signal.

  • And we'll talk more about what it means to receive and

  • transmit a signal in this video and

  • probably in the next few.

  • So this is where it receives the signal.

  • So this is the dendrite.

  • This right here is the soma.

  • Soma means body.

  • This is the body of the neuron.

  • And then we have kind of a-- you can almost view it as a

  • tail of the neuron.

  • It's called the axon.

  • A neuron can be a reasonably normal sized cell, although

  • there is a huge range, but the axons can be quite long.

  • They could be short.

  • Sometimes in the brain you might have very small axons,

  • but you might have axons that go down the spinal column or

  • that go along one of your limbs-- or if you're talking

  • about one of a dinosaur's limbs.

  • So the axon can actually stretch several feet.

  • Not all neurons' axons are several feet,

  • but they could be.

  • And this is really where a lot of the distance of the signal

  • gets traveled.

  • Let me draw the axon.

  • So the axon will look something like this.

  • And at the end, it ends at the axon terminal where it can

  • connect to other dendrites or maybe to other types of tissue

  • or muscle if the point of this neuron is to tell a muscle to

  • do something.

  • So at the end of the axon, you have the axon

  • terminal right there.

  • I'll do my best to draw it like that.

  • Let me label it.

  • So this is the axon.

  • This is the axon terminal.

  • And you'll sometimes hear the word-- the point at which the

  • soma or the body of the neuron connects to the axon is as

  • often referred to as the axon hillock-- maybe you can kind

  • of view it as kind of a lump.

  • It starts to form the axon.

  • And then we're going to talk about how the impulses travel.

  • And a huge part in what allows them to travel efficiently are

  • these insulating cells around the axon.

  • We're going to talk about this in detail and how they

  • actually work, but it's good just to have the anatomical

  • structure first. So these are called Schwann cells and

  • they're covering-- they make up the myelin sheath.

  • So this covering, this insulation, at different

  • intervals around the axon, this is

  • called the myelin sheath.

  • So Schwann cells make up the myelin sheath.

  • I'll do one more just like that.

  • And then these little spaces between the myelin sheath--

  • just so we have all of the terminology from-- so we know

  • the entire anatomy of the neuron-- these are called the

  • nodes of Ranvier.

  • I guess they're named after Ranvier.

  • Maybe he was the guy who looked and saw they had these

  • little slots here where you don't have myelin sheath.

  • So these are the nodes of Ranvier.

  • So the general idea, as I mentioned, is that you get a

  • signal here.

  • We're going to talk more about what the signal means-- and

  • then that signal gets-- actually, the signals can be

  • summed, so you might have one little signal right there,

  • another signal right there, and then you'll have maybe a

  • larger signal there and there-- and that the combined

  • effects of these signals get summed up and they travel to

  • the hillock and if they're a large enough, they're going to

  • trigger an action potential on the axon, which will cause a

  • signal to travel down the balance of the axon and then

  • over here it might be connected via synapses to

  • other dendrites or muscles.

  • And we'll talk more about synapses and those might help

  • trigger other things.

  • So you're saying, what's triggering these things here?

  • Well, this could be the terminal end of other neurons'

  • axons, like in the brain.

  • This could be some type of sensory neuron.

  • This could be on a taste bud someplace, so a salt molecule

  • somehow can trigger it or a sugar molecule-- or this might

  • be some type of sensor.

  • It could be a whole bunch of different things and we'll

  • talk more about the different types of neurons.

We could have a debate about what the most interesting cell

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B2 中高級

神經元的解剖 (Anatomy of a Neuron)

  • 52 11
    Cheng-Hong Liu 發佈於 2021 年 01 月 14 日
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