If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

Overview of neuron structure

This video introduces the structure and structural types of neurons.  By Matt Jensen. Created by Matthew Barry Jensen.

Want to join the conversation?

  • hopper happy style avatar for user singhalm10
    What is the purpose of nodes of Ranvier?
    (10 votes)
    Default Khan Academy avatar avatar for user
  • leaf red style avatar for user Jack McClelland
    What is a some and how is it different than a regular cell?
    Edit: yes, I did mean soma. Thanks, Brooke!
    (3 votes)
    Default Khan Academy avatar avatar for user
    • leaf green style avatar for user Brooke
      I think you mean a soma. A soma is just a fancy word for the cell body of a neuron. By 'cell body' we sort of mean the part of a neuron that looks like a regular cell (i.e., the part where it keeps it's nucleus and some of the 'regular' organelles. Neurons also have dendrites (the branches) and an axon (the stalk) that make them distinctive from 'regular' cells.
      (22 votes)
  • leaf green style avatar for user Raphaël
    In a pseudounipolar neuron, since the periphery axon has the trigger zone instead of the soma, is the soma useless? If not, then what is it's function?
    (7 votes)
    Default Khan Academy avatar avatar for user
    • blobby green style avatar for user nezamz7218
      I believe that the soma is needed for the survival of the cell, because it can provide ATP, and it does bring the neuron into neuron resting potential via. Sodium Potassium Pump. (powered by ATP) Also soma includes all organelles (most) And it has all the DNA, so basically for survival.
      (4 votes)
  • leaf green style avatar for user evmcdade
    What is a soma?
    (2 votes)
    Default Khan Academy avatar avatar for user
    • leaf green style avatar for user Joanne
      Soma means 'body' . In neurons, which are complex cells, it is used to mean the cell body, a larger area with the nucleus. Neurons typically have dendrites, a soma, and an axon, each with a particular job. Soma is also used when differentiating body cells, somatic cells, with 46 chromosomes from sex cells, the sperm and ova, with 23 chromosomes. Speaking of chromosomes, look another soma! That word means chroma, colorful and soma, body, and those colorful bodies were pieces of DNA they saw under the microscope.
      (3 votes)
  • piceratops ultimate style avatar for user Jazk38
    Why can't the axon terminal connect to something else other than a neuron, muscle cell, or a gland cell?
    (3 votes)
    Default Khan Academy avatar avatar for user
    • piceratops sapling style avatar for user Katherine Terhune
      It can. Axons in the peripheral nervous system going to target cells will contact other cell types, it's how the nervous system relays information to other cells in your body. A good example that has been studied a lot is the neuromuscular junction, where an efferent axon meets a skeletal muscle cell.
      (0 votes)
  • blobby green style avatar for user khairulkafee
    At you said that the unipolar neuron exists in the peripheral nervous system, but what i am confused about is all the other neurons you mentioned after that. Do those neurons ( bipolar, multipolar, and pseudounipolar ) exist in the peripheral or central nervous system?
    (2 votes)
    Default Khan Academy avatar avatar for user
    • duskpin ultimate style avatar for user Betty :)
      The bipolar, multipolar, and other structures of neurons exist throughout the peripheral and central nervous system. The only type of neuron which is limited to a specific system, are the interneurons (which is a functional category, not a structural) which are only found in the central nervous system.
      (1 vote)
  • blobby green style avatar for user Lydia Patton
    So, say you have surgery and an axon is severed. What would happen?
    (1 vote)
    Default Khan Academy avatar avatar for user
    • female robot grace style avatar for user Fire Bird
      Although neurons cannot replicate (mitotically divide), in many cases they may be able to regenerate (repair themselves) after having been traumatized. Experiments in vitro suggest that even axons in the CNS can be stimulated to regenerate to an appreciable extent if an appropriate environment is provided. Hope this helps..
      (3 votes)
  • leaf orange style avatar for user Adrien PYB
    Do human actually have "real" unipolar neuron? Looking at other resources online, it looks like what is called unipolar often refers to pseudounipolar neuron...
    And if we do, what function do they have? Where do we (mainly) find them?
    (1 vote)
    Default Khan Academy avatar avatar for user
  • leaf green style avatar for user Nico van Aalsburg
    How fast exactly is the messaging going? To me it seems like it is going with the speed of light.. Is that correct?
    (1 vote)
    Default Khan Academy avatar avatar for user
    • female robot grace style avatar for user Fire Bird
      The speed of these signals depends on how fast the exchange of charged ions is inside and outside of the cell membrane. The main ions involved are sodium, potassium, chloride, and calcium. Messages in the brain can travel at speeds up to 268 miles/hour. Hope this helps!!
      (2 votes)
  • blobby green style avatar for user abdelrahman.mohsen
    at you mentioned that the axon can transport the nerve impulses from soma to the terminals and vice versa that it can carry the impulses again but in the previous video he said that the axon sends while the dendrites receive. I'm confused now!
    (1 vote)
    Default Khan Academy avatar avatar for user
    • leaf green style avatar for user Joanne
      Stick with dendrites receive, axons carry and the terminals release. There is no reverse miles it is in the lab underexperimental conditions. So, to summarize, dendrites are receptors, axon carry the axon potential if threshold is reached at the axon hillock or trigger zone and the axon terminal releases that neuron' s neurotransmitter.
      (2 votes)

Video transcript

In this video, I want to provide an overview of neuron structure. Neurons in adults have a soma. It's also called a cell body-- soma. And they have processes called neurites, which are divided into dendrites and axons. Dendrites are usually short, branched processes that are often covered in small spines that increase their surface area and perform some other functions. So these are dendrites. And then the other neurite they have is called an axon, which is usually long and unbranched until it reaches its end. So this is the axon. The area where the axon leaves the soma is called the axon hillock. The axon may be short or it may be very long, up to one meter or more. And it usually is unbranched for most or all of that length, until it gets to the end, in these structures, which are called axon terminals. And at this point, it will often branch and create multiple axon terminals. The first part of the axon is called the axon initial segment. Or it's also called the trigger zone. And we'll get into the reason for that in the next video. Axons can be so long that they are dependent on systems that transport substances from the soma, which contains most of the organelles, to the axon terminals, and vice versa. Things have to be transported both directions. And the axon is dependent on those systems. Large axons are usually wrapped in a sheath of a material called myelin. And axons that have a myelin sheath have little gaps between these segments of myelin called nodes of Ranvier. So the sheath I've drawn in yellow is the myelin, each of these little segments of sheath here. And these gaps that regularly interrupt the sheath are called nodes of Ranvier, these little gaps in the myelin sheath. The axon terminals will come very close to the target cells of the neuron. And I'll just draw it here. So these are the target cells. And these targets cells may be another neuron, they may be a muscle cell, or they may be a gland cell. A few neurons even have axons that terminate on capillaries, to secrete substances called hormones into the bloodstream. The place where an axon terminal comes close to touching the target cell is called a synapse. This is a pretty typical structure for a neuron. But there are multiple structural types of neurons, each of which can be further divided into subtypes. So let's go over some of the big categories of structural types of neurons. In the central nervous system, neurons start as neural stem cells, which turn into most of the cell types of the central nervous system. And these neural stem cells then differentiate into cells called neuroblasts. And don't worry about the details here. Because we'll go into a lot more detail in other videos on development of the nervous system. But neural stem cells and neuroblasts look pretty similar. They're basically just shapeless cells without processes. Neural stem cells can become almost any neural cell of the central nervous system, while neuroblasts can only become neurons. Neuroblasts will then migrate away from the neural stem cells to the location that their somas will have after development. Neuroblasts then extend a process, which is an axon, toward their target cell. And that axon is tipped with this structure called a growth cone-- growth cone. The axon growth cone follows guidance cues in the environment until it reaches the target cell of the neuron. A similar process occurs for neurons in the peripheral nervous system. But the original and the migrating cells for those neurons are neural crest cells, instead of neural stem cells and neuroblasts. Neurons at this stage have only one process, which is an axon. So they are now called unipolar neurons-- unipolar. That's the structural type of this neuron because there's one pole to the cell, one process giving a sense of direction on this otherwise shapeless cell. Unipolar neurons are present in humans, mainly during development. The next structural type of neuron has a soma. And it has one axon. But it also has one dendrite. So since this structural type of neuron has two processes, or two poles, it's called a bipolar neuron-- bipolar. The next structural type of neuron has a soma, just like the others, and one axon. But it has multiple dendrites. And so since it's going to have multiple poles, it's called a multipolar neuron-- multipolar. And this is the most common structural type of neuron in adult humans. The last big category of structural types of neurons is a little different. It has a soma, like all the rest. And then it has one a short process coming out of the soma, that then divides into two long processes going in different directions. And these are both axons. The axon bringing information in from the periphery is called the peripheral axon. And the axon bringing information into the central nervous system is called the central axon. The very end of the peripheral axon acts a lot like dendrites do on the other structural types of neurons. And we'll start to go over the function of dendrites and axons in the next video. And then this part of the peripheral axon near the end is the axon initial segment, where the trigger zone, just like this part is on a multipolar neuron close to the soma. And just like in these neurons where this is the trigger zone, and then the end of the axon has the axon terminals, in this type of neuron this is the trigger zone of the axon. And then the axon terminals are all the way at this end of the central axon. So this type of neuron has a big, long, funny name. It's called a pseudounipolar neuron-- pseudounipolar. And the reason is that it's kind of, sort of like a unipolar neuron, with only one process coming out of the soma. But that little short process immediately splits into these two long axons. So it's really a different shape than the unipolar neurons.