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Synapse structure

Created by Matthew Barry Jensen.

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  • starky ultimate style avatar for user Iris S
    What functions does that astrocyte fulfill? Why is it there?
    (24 votes)
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  • male robot donald style avatar for user Nikhil Prabhu
    I assume electrical synapses are faster since they are a direct connection between membranes and also require lesser resources than a chemical synapse. If I am right, why aren't there more electrical synapses than chemical synapses in the brain. In other words what are the advantages of a chemical synapse over electrical ones?
    (7 votes)
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    • duskpin ultimate style avatar for user Rafael Freitas Azevedo
      The main advantage is for the computational properties of the brain; while an electrical synapse can only represent one type of signal, a signal in a chemical synapse can have several different effects on the postsynaptic cell, depending on the receptors that the post-synaptic terminal has. If you go on a little more about this topic you will find out about excitatory post synaptic potentials and inhibitory post synaptic potentials, wich should give you a clearer insight on the matter
      (11 votes)
  • blobby green style avatar for user dfwtkd2010
    where can i find about resting potentials
    (5 votes)
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    • leaf blue style avatar for user eira
      I think you would appreciate "health and medicine" -> "advanced nervous system physiology" -> "neuron membrane potentials" , in which the two first videos are called "neuron resting potential description" and "neuron resting potential mechanism"
      (5 votes)
  • blobby green style avatar for user p g
    How does the action potential make it to the proper axon terminal? Are there signal waveform variations or do all of the axon terminals send the same transmitter?
    (3 votes)
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    • orange juice squid orange style avatar for user Joshua Dietz
      signal wave form down the axon until the terminal, at the terminal it ejects packets of neuro-transmitters across the gap. There are a huge amount of neuro-transmitters so it is quite possible that more then one will be ejected depending on the need and the type of job the neuron plays in the surrounding tissue
      (2 votes)
  • winston baby style avatar for user Wondergeek
    What is the difference between dendrites and synapses? Is information received by the dendrites, travel to soma, axon, and then information is transmitted by axon terminal to a dendrite of another neuron?
    (3 votes)
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    • orange juice squid orange style avatar for user James Hill
      Dendrites are the afferent out-branchings of the neural cell bodies, which receive incoming graded potentials, transmitting them to the cell body where they can stimulate the production of an action potential that travels down the axon. Synapses are less of a physical structure such as dendrites, but instead they are the "junctions" between two neural cells (i.e. the synapse between an interneuron in the spinal cord and a motor neuron is the location where the axon of the interneuron excites the dendrites of the motor neuron by releasing neurotransmitters into the SYNAPTIC-cleft/space)
      (2 votes)
  • blobby green style avatar for user kenmburugu.KK
    describe the potassium channels and calcium channels In the synapse
    (2 votes)
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    • leafers ultimate style avatar for user William H
      There are protiens in the synapse, that when the voltage difference (difference in + and - charge) is great enough will open and change the voltage, causing others to open along the way. Once it reaches the end it activates calcium channels which cause neurotranmitters to be released.
      (2 votes)
  • duskpin ultimate style avatar for user Victoria
    is there really a synapse if the neurons are touching?
    (2 votes)
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  • blobby green style avatar for user LilBigMan1274
    explain the structure of a synapse
    (2 votes)
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    • piceratops ultimate style avatar for user ILoveToLearn
      Presynaptic neurons release pre-packaged neurotransmitters by exocytosis via SNARE proteins that anchor the synaptic vesicles to the presynaptic cell membrane. Quantal release (synchronized neurotransmitter release) follows.
      The neurotransmitters bind to postsynaptic receptors and affect a change in that cell, either by activating second messengers or by initiating/suppressing an action potential, etc.
      Temporal and spatial summation can also be discussed here, as can factors that influence cell excitability.
      Your question is rather vague, so if you continue to have a specific question, I would be happy to answer it.
      (2 votes)
  • mr pink red style avatar for user Paulius Kantakevicius
    why does axon terminals connect with each other? Does it enchance somehow the signal that the other axon will give to following cells?
    (2 votes)
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  • male robot hal style avatar for user Sandhaya  Tripathi
    At , when the axons come in contact with the axons of another neutron's axon, why doesn't it just go directly to the target?
    (2 votes)
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Video transcript

In this video, I want to talk about the structure of the synapse. Synapses are where neurons contact and communicate with their target cells, and the word "synapse" comes from Greek words meaning "to clasp together." So let me start by showing where synapses happen, so first I'll draw the soma of a neuron in red, and a few dendrites, these branching processes of neurons in blue, one dendrite and here's another dendrite. And then I'll draw the axon of the neuron in green. It's this long unbranched process, until it reaches the end, and then it branches into multiple terminals, and I'll just draw a few here, but it can have many, many terminals. And then let me just draw some target shapes to represent the types of target cells that a neuron may contact with the synapse. And these cells may be another neuron, they might be a muscle cell, or they may be a gland cell, and some neurons even have axon terminals that end on blood vessels to secrete substances into the bloodstream, called hormones. So synapses are these spots, where the axon terminals of a neuron are contacting their target cell, and there are a couple of types of synapses, one of which has a gap like I've drawn here, although it's actually a much smaller gap than I've drawn, and the other one doesn't have a gap. They are physically connected. The type of synapse that has a gap is called a chemical synapse, because it releases molecules, or chemicals, at the synapse that cross from the axon terminal to the membrane of the target cell. The other type of synapse is called an electrical synapse. And with this type of synapse, the cells are actually physically connected, so that the axon terminal physically connects with the membrane of the target cell, and there are special channels called "gap junctions" that actually let the inside of the neuron communicate with the inside of the target cell. The cytoplasm of the two are really connected, and ions can flow directly from the neuron into the target cell. In this set of videos, I'm just gonna talk about the chemical synapses, where there is a gap, because they are far and away more common than electrical synapses, which are fairly rare, at least in humans. Now a typical human neuron can have a massive number of connections through synapses. It can connect thousands of different target cells through its axon terminals, and the typical neuron receives information through thousands of synapses. Most of those synapses come in to the dendrites, so that the axon of another neuron is contacting and communicating with the dendrite of this neuron, and there could be many, many synapses on a dendrite, and part of the reason it's branched, is just so that it can have more surface area, to form more synapses. So that for most neurons, most of the synapses are actually coming in through their dendrites. However most neurons also do get a smaller number of synapses coming in to the soma. And there are even synapses onto the axon, but usually not just anywhere onto the axon, it's usually onto the axon terminal, so that this axon comes in, and its axon terminal is synapsing on the axon terminal of this neuron. And it could be the same with this axon terminal, it could have synapses, and this axon terminal right here. And so try to imagine thousands of synapses just literally covering this whole neuron, and that it in turn is connecting with thousands of target cells through synapses. And you can just imagine how complex the information is that's flowing into and out of the neuron from other parts of the nervous system. But now let's zoom in, and let's look at the structure of an individual synapse, like for instance this synapse right here. Let me start by drawing a big axon terminal, so I'll just blow up that axon terminal and make it really big here in green, and then I'll just draw a target type of shape to represent the target cell, which again could be another neuron, could be a muscle cell, or it could be a gland cell. And then in the central nervous system, covering most of the synapses are the end feet of astrocytes. Now let me just draw that in purple, and I'll actually just label that, let me just write "astrocyte," and this would be one of the end feet of the astrocyte that, in the central nervous system are just plastered all over synapses. So for a chemical synapse like this, there is a gap here, between the membrane of the axon terminal of the neuron, and the membrane of the target cell. And the gap is actually much smaller than this, but I just needed a little room to draw. It's a very, very small gap, but the cells are not actually physically touching each other. There is a gap. And we call this gap the synaptic cleft. Let me just write that out - synaptic cleft. And that's the space between the neuron and the target cell, and then we have names for this piece of membrane over here, and this piece of membrane. This membrane facing the synaptic cleft, on the axon terminal of the neuron, we call the presynaptic membrane, presynaptic membrane is right here, because it's before the synaptic cleft. And then this piece of membrane on the target cell facing the synaptic cleft is the postsynaptic membrane, postsynaptic membrane, and that's right over here. And so it's presynaptic because it's before the synaptic cleft, and it's postsynaptic because it's after the synaptic cleft. Just on the inside of the presynaptic membrane are vesicles, which are little membrane-enclosed bubbles inside the cytoplasm of the neuron, and these are called synaptic vesicles. Synaptic vesicles - that's each of these bubble-like structures just inside the presynaptic membrane of the neuron. And these synaptic vesicles are full of molecules called neurotransmitter. Let's draw a couple of dots in here to represent these molecules, and they are called collectively neurotransmitter, because they transmit information from the neuron to the target cells, and all of these molecules are collectively called neurotransmitters. And there are different types of neurotransmitters, that we'll get into on other videos. On the postsynaptic membrane are receptors that are specific for the neurotransmitter in the synaptic vesicles. The neurotransmitter will fit like a key in a lock to these neurotransmitter receptors on the postsynaptic membrane. And in the next video we'll talk about how the neurotransmitter and the synaptic vesicles is released from the presynaptic membrane to cross the synaptic cleft, and bind to its receptors on the postsynaptic membrane.