019 What is Summation? (2 Types)

019 What is Summation? (2 Types)

Leslie Samuel IBTV, The Nervous System 150 Comments

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.

175 comments
Robert Edwards Jr
Robert Edwards Jr

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

Mutuma Kimaita
Mutuma Kimaita

this video is awesome. your explanations are clear and precise. keep up the good job.

smilebeautifulworld
smilebeautifulworld

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.

Putenschnitzel Sodla
Putenschnitzel Sodla

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 :)

Glenda V.
Glenda V.

you are soooo awesome!! you are helping a lot!!

Alex Kubik
Alex Kubik

Great video, Chap! Cheers from Australia!

nanadiivadoll
nanadiivadoll

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? :)

Rowella Bacwaden
Rowella Bacwaden

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

Ray
Ray

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 :)))

kostasaekara
kostasaekara

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?

ringsanoj99
ringsanoj99

You sir are immensely awesome. Thank you very much! :)

mamaeesh
mamaeesh

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!

Tom T
Tom T

So great! Helped so much!

daisytigler
daisytigler

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!

Tamoto08
Tamoto08

Thank you for your videos! They are very helpful to me and make Biology fun.

skomura
skomura

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

Chloe Hess
Chloe Hess

Thank you!!!! You made the information much more clear for me!

Jumana Altheeb
Jumana Altheeb

Very helpful !! made it much easier for me to understand. Thank you so much :)

hphs50
hphs50

Extremely helpful. Thank you!

LastSparkle
LastSparkle

thank you so much! you've probably saved me from a bad mark tomorrow. oh and - best wishes from germany :)

patricia campos
patricia campos

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 ;)

artiosarri
artiosarri

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!

joeaiello2
joeaiello2

Fantastic description. Thank you

barissimo111
barissimo111

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

anilynh
anilynh

Thank you so much! I stared at my textbook for 30 minutes and was so very confused!

zbrooo
zbrooo

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.

miss.v ee
miss.v ee

My gosh ..u are great! My teacher with a Ph.D couldnt even explain this :/

praveena reddy
praveena reddy

This video really helped me...thank you so much...!!!!

praveena reddy
praveena reddy

This video really helped me...thank you so much...!!!!

mjegan72
mjegan72

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!!

versatilevoices
versatilevoices

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

christine8767
christine8767

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