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Anatomy of a neuron

Neurons (or nerve cells) are specialized cells that transmit and receive electrical signals in the body. Neurons are composed of three main parts: dendrites, a cell body, and an axon. Signals are received through the dendrites, travel to the cell body, and continue down the axon until they reach the synapse (the communication point between two neurons). Created by Sal Khan.

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  • blobby green style avatar for user Boaz Yip
    How does Myelin Sheath increase the transmission rate?
    (141 votes)
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    • aqualine ultimate style avatar for user Jason Chodakowski
      So in order to understand why a myelinated axon propagates a signal faster than an umyelinated axon you have to understand that passive current flow (electrotonic spread or electrotonic potential) travels much faster than a propagation of action potentials. The downside is that in a cell these electronic potentials attenuate quite rapidly and are therefore unsuitable for long-distance signaling. Myelination serves to insulate the axon to take as much advantage of electrotonic spread, before offering a node which can "regenerate" the signal via an action potential. Action potentials appear to jump from node to node, but they're really connected by the very rapid electrotonic current being conducted between the nodes.
      (152 votes)
  • blobby green style avatar for user travisclintvoita
    Is it true that Schwann cells form the mylein sheaths for neurons in the Peripheral Nervous System, and Oligodendrocytes form the mylein sheaths in the Central Nervous System?
    (46 votes)
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    • orange juice squid orange style avatar for user Kaius J
      In addition to the previous answers we have 3 more types of Glia Cells:
      Oligodendrocytes (Myelinating)
      Astrocytes (Blood-Brain Barrier)
      Microglia (Fagocytotic cells, participate in immundefence)

      Schwann Cells (Myelinating)
      Satellite Cells (around parasympathic and sympathic nerves and regulate outer chemical environment - Resembles astrocytes in CNS to some extent)
      (6 votes)
  • female robot grace style avatar for user Vivian Cribb
    Can certain circumstances cause neurons to work incorrectly, and what are the consequences?
    (10 votes)
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    • piceratops tree style avatar for user Nachiket  Jambhekar
      Neurons are very important to the body but as it is a cell it will have to die or get injured. The to much of death of neurons results fatal diseases like Alzheimer's,dementia mental retardation etc. the remaking of neurones is known of neurogenesis which doesn't take place in humans . Less oxygen supply less glial cells may lead to neural death and malfunction of the neurons
      (4 votes)
  • piceratops tree style avatar for user Abhigyan Shankar
    Why doesn't Mylein Sheath completely cover the axon?
    (6 votes)
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  • piceratops ultimate style avatar for user Isabelle Early
    If each neuron gets a signal from another neuron, what is the origin of the signal?
    (2 votes)
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    • orange juice squid orange style avatar for user shatadal.alankrit.13
      The origin of the signal is the stimulus, something happening outside the body, that is received by a sensory neuron, relayed to the brain, and responded to via motor neurons. There are receptors in the skin that sense heat, depth, and texture. Our eyes form images on the retina. Auditory information is sensed by movement of liquid in the cochlea, which makes little hairs move and trigger nerves. Some stimuli don't get relayed to the brain but instead respond with instinctive motions in a reflex arc, but that is usually not the case.
      (14 votes)
  • male robot hal style avatar for user makemakebirthdaycakepebblecarracingmilk
    Since most or all of the neurons are connected, does that mean diseases or tumors spread faster in the brain compared to other parts of the body?
    (5 votes)
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    • female robot ada style avatar for user Lidiya
      No, the disease or tumor spread does not depend on how neurons are connected. Moreover, primary brain tumors are considered to be the slowest growing tumors. This is because neurons do not proliferate, a factor that is necessary for a genetic mutation to accumulate in neoplastic tissue through clonal selection. Primary brain tumors represent only 2% of all cancers and the incidence is peaking at age 85 years. This is different for brain tumors of glial (non-neuronal) origin, which are quite aggressive, but the question is about neurons and neuronal connections as I understand.
      (8 votes)
  • mr pink green style avatar for user Vansh Sharma
    Can we say Neurons are kind of wires of a circuit? I mean they do kind of the same function, don't they? And we are kind of highly advanced machines running on mainly two very complex circuits Heart and Circulatory System, & Brain and Nervous System, isn't it?
    (5 votes)
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    • winston baby style avatar for user Ivana - Science trainee
      Neurons? Yes. They have axons and dendrites - which help create neuronal synapses. Axons conduct neuronal signals.

      You can say that we are highly advanced machines running on many complčey circuits. The physiology, molecular biology of the brain is very complex. Electrical and chemical synapses are interesting as well.
      (5 votes)
  • male robot hal style avatar for user Alex Chiu
    What is the difference between the Schwanne cell and the myelin sheat? Is the myelin sheat the purple part he draw or plus the axon?
    (4 votes)
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  • male robot hal style avatar for user Dakshina Sarma
    at sal mentions "action potential". what is it?
    (4 votes)
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    • old spice man green style avatar for user Matt B
      An action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. You will see this often in physiology, particularly is neurons because this is how signals travel through our bodies
      (5 votes)
  • starky ultimate style avatar for user Siddhey Nagpure
    What is the function of Soma ?
    (4 votes)
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    • blobby green style avatar for user liweiong272
      The soma, also known as the cell body, is the factory of the neuron. It produces all the proteins for the dendrites, axons and synaptic terminals and contains specialized organelles such as the mitochondria, Golgi apparatus, endoplasmic reticulum, secretory granules, ribosomes and polyribosomes to provide energy and make the parts, as well as a production line to assemble the parts into completed products.
      (4 votes)

Video transcript

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.