Action Potential

by Thad Wilson, PhD

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    00:01 What do you do with all of these current changes, ion changes inside and outside the cell and determining which channel is open? Well, we can put them all together and create a membrane potential.

    00:16 Membrane potential changes are important for signaling.

    00:20 Things like a nerve will use an action potential to move information and ions down its neuron.

    00:30 So, let’s go through what this process looks like.

    00:34 In green here, we have an action potential.

    00:37 We start at a resting membrane potential of minus 70, there’s a gradual increase, then there’s a steep increase, it goes above zero just a little bit and then it downward fall to below resting membrane potential and a gradual climb back to resting membrane potential.

    00:57 This is the membrane’s potential, not any one ion.

    01:03 So what are some points about this that we need to remember? Because you do need to remember what an action potential looks like.

    01:10 And I guarantee, if you invest the time now, you will be better for it.

    01:15 You’ll do better on exams because you will understand how this process works and be able to replicate it whenever you need to, quickly.

    01:26 The points that we want to go through are which channels are going to be open.

    01:32 Let’s start with sodium.

    01:35 This first portion of the current is a sodium channel opening.

    01:42 Sodium channels open rapidly and then deactivate rapidly.

    01:47 This is the cause for the initial upward trajectory after you’ve reached what we’d like to call threshold.

    01:57 You might ask, well, what is threshold? Threshold is when you have reached a voltage to open up these sodium channels.

    02:07 They open up at a particular voltage and as soon you get to that voltage boom, those channels open and then, boom, they close.

    02:18 That initial rise or depolarization is caused by sodium.

    02:23 Why did it want to go up? Because sodium wants to travel from an area of high concentration to low, from outside the cell to inside the cell.

    02:32 Its neuron’s potential was 61, it never actualized its potential.

    02:38 So always sad when something doesn’t actualize its potential.

    02:42 But in this case it shut off before it could get to the point where it wanted to.

    02:49 How did it close? It’s pretty much on a timer system.

    02:54 It will open up for a brief period of time and then will close and it’s very difficult to keep it open for longer than that brief period of time.

    03:05 The next thing that happens is a potassium current.

    03:09 Potassium then comes out of the cell because the gradient is from within the cell to out of the cell.

    03:16 So potassium channels open and then deactivate.

    03:21 Hopefully, you’ve noticed from this response that potassium is a little bit slower to open and a little bit slower to deactivate, and that allows for that current then to fall back down even to a little bit below baseline.

    About the Lecture

    The lecture Action Potential by Thad Wilson, PhD is from the course Membrane Physiology.

    Author of lecture Action Potential

     Thad Wilson, PhD

    Thad Wilson, PhD

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