The resting potential is a measure of an inactive axon’s difference in electrical charge across its membrane, measured by a voltmeter. The inside of the membrane is -70 millivolts (mV) relative to the extracellular side, which is a store of potential energy that can be used at a future time. A resting axon’s fluid interior contains both large, negatively charged protein ions and smaller, negatively charged potassium ions. The axon’s surface is selective about what it allows through its “gates”.
A neuron at rest is negatively charged, with the inside of a cell being approximately 70 millivolts more negative than the outside (-70 mV). This voltage is known as the resting membrane potential, which is about -60mV. A neuronal action potential gets generated when the negative inside the cell is negative.
The axonal membrane is polarized at rest, and the resting potential is maintained by the sodium-potassium pump, which moves two potassium ions (K+) into the neuron and three sodium ions (Na+) out of the neuron. This maintains the mostly negative charge of the axon’s fluid interior due to the presence of large anions and negatively charged proteins.
The situation is different for organic anions present in the interior of the cell, often negatively charged amino acid side chains in proteins. In resting squid axons, there is an electric potential of about 60 mV across the plasma membrane, with the inside of the cell negative with respect to the outside.
In summary, the resting potential is a crucial aspect of the electrical behavior of neurons, affecting their ability to generate electricity from chemical elements. The axon’s fluid interior contains both large and small negatively charged ions, ensuring the stability and functionality of the neuron.
📹 Action Potential in Neurons, Animation
(USMLE topics) What is Action Potential? How is it Generated in Neuron? Clear and Concise Explanation of Phases. Purchase a …
📹 Neurology | Resting Membrane, Graded, Action Potentials
In this lecture Professor Zach Murphy will present on resting membrane, graded, and action potentials! We will be discussing the …
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0:18 ACTION POTENTIAL: A brief reversal of electric polarity across the cell membrane. 0:44 RESTING MEMBRANE POTENCIAL RMP (neuron): -70 mV (cell is more negative in the inside.) 1:23 A neuron is typically stimulated at dendrites and the signals spread through the soma. 1:28 DEPOLARIZATION: Excitatory signals at dendrites open ligand-gated sodium websites and allow sodium to flow into the cell -> makes membrane voltage less negative. 1:49 Influx of sodium produce a current that travels towars the axon hillock. 1:49 If the summation of all input signals is excitatory and strong enough when it reaches the axon hillock -> action potencial is generated (travels to the nerve terminal). 2:08 Axon hillock: “trigger zone” (where action potential usually starts -> voltage-gated ion websites concentrated). 2:27 Voltage-gated ion websites open at some values of the membrane potential and close at others. 2:45 THRESHOLD: -55 mV -> Minimun required to open voltage-gated ion websites -> action potential generated. (Na+ websites open quickly / K+ websites open slowly) 3:07 As sodium rush into the cell, the inside becomes more positive (depolarization). 3:18 The increasing voltage in turn causes even more sodium websites to open (positive feedback) -> Rising phase of the action potential (polarity reversed). 3:37 As the action potential nears its peak, Na+ websites begin to close -> K+ websites are fully open. 3:47 K+ rush out of the cell -> voltage returns to its original resting value (falling phase of the AP).
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Hi, that was a brilliantly informative article and answered alot of questions I had very easily where the text from my professor didn’t. One question I have is where the negative charges to make up the 70mV came from? Is it from Cl ions from the splitting of NaCl? I understand the overall internal negative charge is coming from the fact more positive ions flow out than come in so there is an overall negative charge internally (3 Na+ out for every 2 K+ in) but I’m just unsure of where the negatively charges ions have appeared from.
why do sodium ions keep entering the axon during the action potential? if its facilitated diffusion, shouldn’t the two sides reach an equilibrium? how comes there’s a higher Na+ concentration inside the axon during the AP but more STILL enters? isn’t that active transport against a concentration gradient? can’t wrap my head around that bit
I wish my professors had just one percent of enthusiasm for their teaching. they’re probably into whatever they’re researching, but they don’t give a shit about how amazing all of this is for someone who is just learning about it, but no matter how well you know your stuff, you never fail to infect me with your enthusiasm. whenever I have a new incompetent professor I come to your website to find my passion for what I’m studying again and I can’t thank you enough for what you do.
I honestly don’t write comments, but man it really does take some serious genius-like skills to be able to teach the way you do. I’ve been struggling to piece it all together, remembering learning bits and bits over the years. Now, I feel like my mind is finally at peace. I wish you taught at my school 😭
Temporal Summation. TaTaTa! Just keeps bugging you! Ahahaha! Until you hit a threshold potential. Ahahaha! By the way; when you say “Alright Ninja Nerds”; it really is nice; honestly; it’s a small little detail; but it makes you feel like your back at one of your favorite classes! It makes you feel like someone who doesn’t even know you; really actually cares about you; almost like a dad getting ready, and excited, to teach his kids. It’s awesome Zach! Ninja Nerds is dope!
you are a life saver. you really help me through, you make really complicated things simpler with colors, diagrams and explanations. once I come out of med school, no matter where I am in this world, I will come and meet you to thank you personally for the wonderful efforts you put in your articles, so that people like me can become life saving doctors one day. much respects. god bless you and I hope you get everything you want in life.
I am a little confused, are sodium and potassium leaky websites the same as voltage-gated sodium and potassium websites? Some books mention leaky websites responsible for reaching the resting membrane potential others used voltage-gated websites. If they are different what is the contribution then to the resting membrane potential?
So the pump provides about -5mV and the rest is due to K+ leaving the cell. BUT that K+ is replaced by the action of the pump, so why doesn’t the K+ coming in cancel out the K+ going out? Also, assuming the pump corrects for ion leakage (which is the usual explanation) more Na+ leaves (due to the pump) than gets in (through leak websites) so why doesn’t the Na+ concentration gradient continually shift?
i have my finals in a week and I know all the individual topics but nothing ever made sense on how they connected, I HAD NO IDEA graded pot are used to raise the rmp to thrrashold and I also had no idea epsp and ipsp were graded intentions, I thought all of them were the same and YOU JUST SAVED MY ENTIRE PHYSIOLOGY EXAM, THANK YOUUUU
Thank you so muchfor those amazing lectures Doc 🧑⚕️🧑⚕️ I started studying dentistry at Cairo University this year 🇪🇬🇪🇬 And i can’t say it enough how much your articles have helped me ❤️❤️ I really love you so much 😘 I don’t know how you can make it so much fun 😊 But thank you for doing it I just wanted you to know how far your YouTube website has got And please excuse my English
I honestly don’t write comments, but man it really does take some serious genius-like skills to be able to teach the way you do. I’ve been struggling to piece it all together, remembering learning bits and bits over the years. Now, I feel like my mind is finally at Hell. I wish you taught at my school
this really clarified my understanding on the concept of action potentials!! i knew most of the concepts on their own but the picture wasn’t clear in my mind on how to put it all together and you quite literally gave me a visual explanation 🤩 i have an exam on tuesday and your website is definitely going to save me🙏🏽
Thank You for your article! It is really cool explanation! I have one question here. I know that there are excitatory neurons and inhibitory neurons. The first one release glutamate NT, the second – GABA NT, am I right? However all processes about resting membrane potential or graded potential are the same for both. For both neurons, they must first be excited to release the NTs into the synaptic space.
Thanks doc for publishing of this article. Please, Can you tell me about the concentration of ions inside and outside the cell. Means concentrations of which ions higher in side the cell than outside the cell and opposite, during the: 1- Resting membrane potential 2- Action potential 3- Re polarization 4- Refractory period
in my experience, professors and doctors with fake ass soviet union diplomas and +40 years of experience, cannot explain and understand this kind of topic as Zach. After perusal these article lectures, I’ve asked my professor with 40 years of experience in anesthesiology about some details which hiss sorry ass didn’t know, so for a year he was just reading from a paper without understanding shit. bravo, Zach!
I have a doubt, please explain this, at action potential inside the axon, when sodium website opens and Na+ influx takes place, then axoplasma becomes more positive, when positive charges move down the axon, and comes near to another website, how does sodium influx again takes, how come +30mv becomes -55mv(threshold potential) without moving cation out of the cell.
Sir I have a doubt on refractory period topic,sir in that you have explained that the absolute refractory period is complete repolarization phase and relative refractory period is hyperpolarization phase, but sir the absolute refractory period is 1/3rd of repolarization phase and the rest is relative refractory period,so sir if we give second stimulus just before the resting membrane potential we can stimulate the nerve and achieve staircase phenomenon, rest of the topic explaination is best I liked the article so much, hope you will see my comment and make change thankyou sir
35:10 What causes the sodium to travel toward the next website? And why not in the other direction? Once the gate closes and the sodium moves on to the next closed gate to open it, what’s stopping it all from going back toward the closed gate that they had previously opened? What makes it different from a closed gate downstream? I’m curious about the specifics of how charge propagation works. I know action potentials are unidirectional, and it’s because you start at one end of the axon and not somewhere in the middle, but I’m a little lost as to exactly why that is. Could someone please clarify for me? Thank you!
This part is so poorly taught in medicine courses that it really makes it complicated at first. I think it would easier if they first taught the Goldman-Hodgkin-Katz equation and then showed the Nernst equation as the limiting equation when the membrane becomes considerably more permeable to one of the ions.
I think the refractory periods were a bit screwed up… I.e. absolute refractory period denotes the portion of AP from the onset of spike to when the repolarization is atleast one third complete. Relative refractory period is just below this phase, that is until complete repolarization. And in the hyperpolarised state, the membrane subnormally excitable, for obvious reasons.
Thank you so much for this vedio, i had a lot of confusion regarding these ions movements and voltage gates. After a week of using my brains i found it so frustrating and within these few minutes of understanding ( your vedio ) i am really in love with these membrane potentials now. Thank you for your hard work and dedication.
This is wrong. V-rest is not generated directly by the Na/K ATPase. The Na/K pump helps set up a gradient for Na and K, and these conductances drive the V-membrane toward the equilibrium potentials of the conducting ions (mostly K, some Na). A simple proof is to add K to the outside of the cell- you’d see a nearly instant positive shift in V-rest (predicted by the Nernst equation) that cannot be explained by a change in Na/K pump activity.