019 What is Summation? (2 Types)

When post-synaptic potentials reach the neuron, they can be added up through the process of summation.

Watch as Leslie explains this process and expounds on the 2 types of summation.

Enjoy!

Transcript of Today’s Episode

Welcome to another episode of Interactive Biology TV, where we’re making biology fun! My name is Leslie Samuel. In this episode, Episode 19, I’m going to be answering the question “What is summation?” and I’m going to talk about the 2 types of summation. So let’s get right into it.

Summation is basically the addition of post-synaptic potentials. To illustrate this, I’m going to draw our membrane potential graph, with membrane potential on the Y-axis, Em, and time on the X-axis. I’m going to start with our resting membrane potential somewhere around -70 millivolts, so let’s say this is -70. Now, we’ve spoken about threshold, and we said that in order for there to be an action potential, the membrane potential needs to reach that threshold, and I’m going to say that’s around -55 millivolts.

So an action potential comes down an axon, it reaches the axon terminals, neurotransmitters are released, and that causes an excitatory post-synaptic potential in the post-synaptic cell. What you’re going to see there is there’s going to be a little bump in the membrane potential. We know that the threshold is up here, so that bump is not going to be enough to cause an action potential.

So what needs to happen is we get an excitatory post-synaptic action potential, and before the first one finishes, another one comes along, raising the membrane potential even more, and that process continues over and over until eventually, we have enough stimulation to cause the membrane potential to reach threshold. And then, we get the action potential with our depolarization, our repolarization, our hyperpolarization, and then the action potential is finished.

So that’s what we’re talking about with summation. We’re basically adding these post-synaptic potentials. Remember, sometimes we can get excitatory post-synaptic potentials, we can get inhibitory post-synaptic potentials that bring our membrane potential even further away from the threshold. But we’re basically adding them so that we can reach that -55 millivolt threshold and cause an action potential.

With that understanding, let’s look at the 2 types of summation:
1. Temporal summation
2. Spatial summation
I’m going to do a drawing to illustrate both. With temporal summation, what we have is a pre-synaptic neuron, so let’s just draw an axon, and I’m going to simplify it by making just 1 axon terminal, and that makes a synapse with a post-synaptic neuron, so here’s my neuron. Here we have the soma, and here we have the axon. What happens is a signal comes along this axon, comes to the axon terminal, releases neurotransmitters, and that causes an excitatory post-synaptic potential in this cell. That is where we see the first bump. Now, if it sends that signal and it sends another one quickly and it continues doing that, that’s going to cause the membrane potential to go up and up until it reaches the threshold and causes the action potential. This is temporal summation.

Now, that’s different from spatial summation. With spatial summation, we have an axon here, and I’m just going to draw 1 axon with 1 terminal, of course that’s simplified, that connects to another neuron. However, we also have another axon that comes and we have an axon terminal that connects to the same neuron.

What’s going to happen here is this one can cause a signal, an excitatory post-synaptic potential, and before that dies off, we can have another signal coming from this other cell. So we have 2 separate neurons causing responses in this cell, and of course, we get the same result where the membrane potential goes up, and when the next one fires, it goes up again, and this one can fire again, that causes it to go up, and then it eventually reaches the threshold, causing our action potential. That is spatial summation.

So an easy way for you to remember this, at least this is what works for me, spatial summation is separated by space, because we have 2 separate neurons that are firing. Temporal summation is the same neuron firing, but each signal is separated by time. So temporal summation is separated by time, same neuron. Spatial summation is separated by space, because there are 2 separate neurons.

That’s all the content for this video. We’ve looked at the 2 types of summation and we’ve answered the question “What is summation?” If you have any questions, go ahead and leave a comment below, and I’d be happy to get to it. That’s it for this video, and I’ll see you in the next one.



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  • That’s awesome Allison. Glad it helped you to understand the difference. Keep checking back because I’m trying to post new videos almost every weekday. So all the best with your learning 🙂

  • omg.. YOU ARE A LIFE SAVER!!!! Wow wonderful video! I really understand it
    now. reading it from notes and a textbook is nothing compared to visual and
    explaining. It really feels good to actually know whats going on now 🙂
    thanks a lot

  • this is WONDERFUL! thank you so much 🙂 🙂 completely understood the
    content that I was struggling to learn by reading!

  • @25Robbo25 You are welcome a million. Glad you are finding value in the
    content. All the best!

  • Thank you so much ! You amazing ! amazing ! so amazing ! 😀 You the best 😀
    the best . I was so confused in my two hour class and I understand
    everything is a 6 min video :O God bless you.

  • @heregod That’s great. Glad to hear that the video helped you so much 🙂

  • great explanation..
    by the way i still cant understand what mean by generator potential.. so can u explain that to me?

  • A generator potential is the same as a receptor potential. It happens in certain sensory receptors and is graded. In other words, it varies depending on the strength of the stimulus. When it reaches threshold, it causes an action potential in the sensory neuron.

    Hope that helps!

  • Hello! This is a wonderful site and video, but I have a few questions.
    Exactly where is the synaptic cleft between? An axon terminal and the soma?
    Also, can there be an action potential passed to a non-neuron body cell? Or action potentials are only passing from neuron to neuron? If that is true, then what are some of the effects neurotransmitters have on non-neuron body cells when they pass into them?
    Thanks so much!

  • Hi Blessing. Some of your questions are answered in previous episodes.
    1. The parts of a neuron – https://www.interactive-biology.com/164/
    2. Action potentials only happen in neurons. However, there are membrane potential changes that can happen in any cell. That changes the charge across the membrane but does not result in an action potential. It can result in other things. For an example, check out what happens in the eyes – https://www.interactive-biology.com/1862/

    Hope that helps!

  • Very well explained…. and my question is can we then say that every
    action potential generated is a result of summation??

  • thank you. it really enhanced my understanding what I want to ask now is
    that doesn’t each neurone end in several synaptic knobs and the
    pre-synaptic membrane is at the end of the synptic knob. So, could it be
    that synaptic knobs of the same neurone release neurotransmitter ?

  • @stareleades Unfortunately, Leslie is no longer taking requests for specific videos, but he will definitely get to more systems and more Biology topics in the future. He has many to work on at the moment. So stay tuned for more. 🙂

  • @afrprincess07 Glad you liked the video. Please stay tuned for more Biology
    videos coming very soon!

  • this is very helpful, thank you so much for putting this video up!!! do you teach by the way? if you do i need to sign up for YOUR classes!

  • Thank you for this video! I could not understand what summation was the way my A&P book explained, but it totally makes sense now…. and it seems so simple now 😉

  • Thank you for this video! I could not understand what summation was the way my A&P book explained, but it totally makes sense now…. and it seems so simple now 😉

  • Glad to know that you found value on this one. You might also need other Biology videos and resources. Just head on to our site for more of them 🙂

  • i literally felt the light bulb go on in my head…i think this is the first time i had an aha moment…thanku!lol

  • @anjali1129 Lol! Well, that’s good to know! Thank you for watching this video. You can go and check our other Biology videos at the site. We hope you’ll find value in them as much as you found one on this. Have fun!

  • Lol! Well, that’s good to know! Thank you for watching this video. You can go and check our other Biology videos at the site. We hope you’ll find value in them as much as you found one on this. Have fun!

  • Lol! Well, that’s good to know! Thank you for watching this video. You can go and check our other Biology videos at the site. We hope you’ll find value in them as much as you found one on this. Have fun!

  • Does having a small time constant minimize the summation effect ? I don’t get how. Wouldn’t you prefer to have a small time constant in the first place.

  • Hi! Just wanted to say thank you. It was easy to understand all these. It has been a great help for my exam. Looking forward to more videos.

  • Does having a small time constant minimize the summation effect ? I don’t get how. Wouldn’t you prefer to have a small time constant in the first place.

  • @EvelynNLB Sorry, Leslie won’t be able to get back to your inquiry. He’s been very loaded at the moment with a lot of work. Please do stay tuned though as he’ll be adding more Biology videos in the future. Thanks!

  • Sorry, Leslie won’t be able to get back to your inquiry. He’s been very loaded at the moment with a lot of work. Please do stay tuned though as he’ll be adding more Biology videos in the future. Thanks!

  • Sorry, Leslie won’t be able to get back to your inquiry. He’s been very loaded at the moment with a lot of work. Please do stay tuned though as he’ll be adding more Biology videos in the future. Thanks!

  • Great understandable video. Sometimes textbooks just don’t make sense and I have to go find other resources! =)

  • i was so gonna fail my exam- i had it all wrong thank you very much for clarifying

  • you know how to explain…thanks for this video…it made things clearer…

  • Leslie, Thank you so much for your videos. I have a very hard time with understanding how my professor explains things. You ALWAYS do such a great job of explaining things to where I understand it. You make it simple and interesting. Thank you, thank you, thank you! 🙂 You are AWSOME!!

  • Leslie, Thank you so much for your videos. I have a very hard time with understanding how my professor explains things. You ALWAYS do such a great job of explaining things to where I understand it. You make it simple and interesting. Thank you, thank you, thank you! 🙂 You are AWSOME!!

  • I think with a small time constant the action potential in the neurone is over faster and therefore the frequency and therefore strength of the impulses must be much higher in order for temporal summation to occur. This means with a smaller time constant a greater stimulus must be required for the excitatory post synaptic potential to reach threshold.

  • well i did not find a german video of this topic so i searched an englisch one…awesome explanation could not be easier explained really thx

  • My professor did not cover this subject in class however it is on the departmental final. Luckily i found your video, very clear and concise information. Just wanted to say thank you!

  • EXCELLENT!!!!!!!!!!! LOVED IT! made it much easier for me to understand. I have read this section on my textbook several times, but it didn’t make sense to me. Thank you so much! Continue with these great explanations, you make a difference in understanding and also in a grade for a paper 😉

  • thank you so much! you’ve probably saved me from a bad mark tomorrow. oh and – best wishes from germany 🙂

  • Very helpful !! made it much easier for me to understand. Thank you so much 🙂

  • I just wanted to thank you for sharing this video – I was lost until I saw this video!

  • I just wanted to thank you for sharing this video – I was lost until I saw this video!

  • I just want to say your videos are SO so helpful. Im a vet student and wouldn’t be able to pass physiology without you!

  • Your explanations are perfect- to the point, simple, easy to understand without a lot of unnecessary verbiage to confuse me. Great work! 🙂 If I get an A on my final, some of the credit goes to you!

  • hello i have a question. In order to produce an action potential whe have to reach the threshold. But the threshold is not a potential, its an intensity, mesured with amperes, not volts. Could you help me?

  • hello i have a question. In order to produce an action potential whe have to reach the threshold. But the threshold is not a potential, its an intensity, mesured with amperes, not volts. Could you help me?

  • AMAZING videos! I’ve been reading my textbook for hours without understanding any if it and you can make it so clear in 5 minutes!!!! You are amazingly gifted!!! Thank you for sharing your wonderful gifts with us lost souls :)))

  • Hello Leslie….this is great. Do you have discussions on the anatomy of the heart and lungs?

  • If temporal summation is a type of summation where a post synaptic neuron is stimulated by a repetitive firing of a single presynaptic neuron. Then what is spatial synaptic neuron? 🙂

  • hi, I’m from Germany. I used your video to understand this topic due to there are no good german videos…. You speak a understandable English and you present the topic understandable…… greetings from Bavaria 🙂

  • hi, I’m from Germany. I used your video to understand this topic due to there are no good german videos…. You speak a understandable English and you present the topic understandable…… greetings from Bavaria 🙂

  • There’s potential called threshold potential (-55mV) when reached affects certain voltage gated Na+ that when opened give rise for rapid change in membrane potential due to entering of sodium into the cell.

  • Summation that results from the multiple synapses firing at nearly the same time is designated?

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