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Current time:0:00Total duration:7:15

Neuron resting potential description

Video transcript

in this video I want to describe the neuron resting membrane potential which we often just call the resting potential for short so first let me just draw a neuron that'll be a little distorted just so I have room to draw so we'll draw the soma here and a really big axon coming out of the soma and normally an axon is a thin long process coming out of the soma but I just need a little room to draw so I'll do it draw a big thick one and this will be the other part of the soma or the cell body and then I'll just draw one really big dendrite and and like the axon of course these are normally just these little thin processes coming out of the soma but I just need some some space so most neurons at rest meaning when they're not receiving any input have a stable separation of charges across the cell membrane called the resting potential and that consists of more positive charges on a layer on the outside of the membrane and more negative charges in a layer along the inside of the membrane and these charges are ions so the negatively charged ions that are in a layer along the inside of the membrane we also call anions and the positively charged ions in a layer on the outside of the membrane we call cations and this layer of anions on the inside and cations on the outside goes all over the neuron cell membrane all through the membrane of the dendrite and the soma and all along the membrane of the axon and just to be clear there is a mix of anions and cations on both sides of the membrane and I've just drawn plus signs on the outside of the membrane to represent that in the layer against the outside of the membrane there are more cations and anions I've drawn negative signs on the inside of the membrane to represent that in that layer there are more anions and cations and talked about the size of the difference in this separation of charges the convention is to call the outside zero so we just say the outside is zero and we just kind of set that as the reference and then we just refer to a single number on the inside of the membrane which is the difference between the voltage on the outside and the inside or the difference in the strength of the charge separation and this difference can vary between neurons but around negative 60 millivolts would be a real a common resting potential for a neuron so I'll just write a little m in a big V for millivolts that's the value we use to quantify this difference in charge separation and around negative 60 would be a really common resting membrane potential for a neuron the resting potential of neurons is related to concentration differences which are also called gradients of many ions across the cell membrane so there's lots of different ions that have high concentrations outside the neuron compared to lower concentrations inside the neuron or vice versa but a few of these ions are the most important for neuron function the cations are the positively charged ions that are most important for neuron function our potassium and I'll just write that as a k+ sodium which I'll write as an n a plus and calcium which I'll write as a see a 2 plus because each calcium ion has two positive charges and the most important anions for neuron function or negatively charged ions are chloride which I'll write a CL minus and then there are multiple organic anions and so I'll just write Oh a minus to stand for organic anions and there are a bunch of different organic anions inside neurons and other cells most of these are proteins that carry a net negative charge now these five kinds of ions are going to have concentration differences across the cell membranes which we also call concentration gradients and it's different for the different ions if they have a higher concentration inside or outside the neuron the organic anions and the potassium ions have a higher concentration inside the neuron than outside so I'll just represent that by having these letters written large inside the neuron and then I'll write a small Oh a minus to show that there's a smaller concentration of organic anions outside the neuron than inside and the same for potassium I'll write a small k+ outside the neuron compared to a large k+ inside because the concentration of potassium is higher inside the neuron than outside the neuron and the opposite is true for these three ions so the concentration of sodium is much higher outside the neuron than inside the neuron as is the concentration of calcium there's much more calcium outside the neuron and inside and the concentration of chloride ions is also much higher outside the neuron than the inside the neuron each of these ions therefore is going to be acted on by two forces that try to drive them into or out of the neuron the first is an electrical force from the membrane potential because each ion will be attracted to the side of the membrane with the opposite charge opposite charges attract each other and like charges repel each other so if we look at each of these ions and turn the organic anions are negatively charged so they will be attracted to the outside of the neuron where there are more positive charges so the electrical force acting on the organic anions will try to drive them out of the neuron potassium is the opposite it's positively charged so it will be attracted to the inside of the membrane where it's more negative so it's electrical force will try to drive it into the neuron sodium is the same as potassium it's positively charged so it will be attracted to the more negative inside of the neuron chloride is an anion like the organic anions so it's electrical force will try to drive it out of the neuron calcium is a cation like potassium and sodium so it's electrical force will also try to drive it into the neuron but now the second force acting on these ions can be thought of as a diffusion force or it's often called a chemical force related to the concentration gradients across the neuron membrane because particles in solution will always try to move from an area of higher concentration to an area of lower concentration so if we look at the organic anions they're in a higher concentration inside the neuron than outside so their diffusion force will be trying to drive them out of the neuron just like their electrical forces now potassium is a little confused it's electrical force is trying to drive it into the neuron but it has a higher concentration inside the neuron so it's diffusion force is actually trying to drive it out of the neuron sodium has matched electrical and diffusion forces because it has a higher concentration outside the neuron than inside chloride electrical forces try to drive it out of the neuron but because it has a higher concentration outside the neuron it's diffusion force will be trying to drive it into the neuron and calcium's just like sodium it both its electrical and it's diffusion force are trying to drive calcium into the neuron these forces we often call electrochemical driving forces for short and neurons are going to use these forces to perform their functions but before we talk about that in the next video let's talk about how the resting membrane potential is created and how it's related to the concentration differences of some of these key ions