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神经元的解剖

神经元(又称神经细胞)负责传递和接收体内的电信号.神经元主要由三部分组成:树突、胞体和轴突.信号首先被树突接收,传递到胞体,然后继续传递到轴突,最终达到突触(神经元之间的交汇点). Sal Khan 创建

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we could have a debate about what the most interesting cell and the human body is but I think easily the neuron would make the top five and if 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 and and maybe for all of our sentience I think what would easily make it the top one or two cells so what I want to do is first just 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 gonna talk a little bit about how it performs it from its function which is essentially communication essentially a transmitting signals across its lengths depending on the signals it receives so if I were to draw a neuron let me pick a better color so let me draw my brush size a little bit thinner 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 so let me draw the nucleus drum I try my best this is a nucleus just like any cell's nucleus and then the psalmist considered the body of the neuron and then the neuron has these little things sticking out from it that keep branching off and keep branching off maybe it looks something like this I don't wanna 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 addenda dendrites dendrites and they can keep splitting off like that I want to do a fairly reasonable drawing so I'll spend a little time doing that the one last dendrite just like 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 and then 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 and then we have kind of a you can almost view it as a tail of the neuron it's called the axon the axon it a neuron could be you know 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 you know for talking about a dinosaur a long 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 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 poor 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 do my best to draw it like that let me label it so this is the axon this is the axon terminal terminal and you'll sometimes hear the word with the point in which the soma or the body of the neuron connects to the axon is 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 so it's the axon hillock and then we're gonna talk about I think there's a C there we're going to talk about how how the impulses travel and a huge part in what allows them to travel officiously efficiently are these insulating cells around the axon these insulating cells around the axon we're gonna 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 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 so I'll say Schwann cells or myelin myelin sheath and then these little spaces between the myelin sheath just so we have all the terminology from other so we know the entire anatomy of the neuron these are called the nodes of ranvier nodes of ranvier I guess they're named after a Ranveer maybe he was the guy who looked and saw they had these little these little slots here where you don't have myelin sheets so these are the nodes of ranvier so the general idea as I mentioned is that you get a signal here we're gonna talk more about what the signal means and then that signal gets trans actually the signals can be some so you might have one little signal right there another signal right there and then you'll have a 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 large enough if they're large enough they're gonna 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 synapses to other dendrites or muscles and we'll talk more about synapses and those might help trigger other things and so you're saying what's triggering these things here well this could be the terminal end of other neurons axes I saw axons like in the brain they could be this could be some type of sensory neuron this could be on a taste buds someplace so and you know a salt molecule somehow can trigger it or sugar molecule or this might be some type of stress sensor it could be a whole bunch of different things and we'll talk more about the different types of neurons