so in this particular video we are going to be talking a little bit about something called the threshold potential okay it's a little bit of a New Concept but it's also tied into your depolarization and repolarization anyway now before we talk about the threshold potential I want to give you a situation right here situation over here is as follows I'm just drawing out two hands over here and the purple color line is just the axon of a neuron okay and of course the Axon over here both the exons have a resting membrane potential of -70 MTS now on the situation on the right uh someone Taps on your wrist and like you know someone touches your wrist quite strongly and therefore that's a strong stimulus and the situation on the left over there let's for example say a tiny little ant is just walking on your wrist and it's a weak stimulus now I'm going to ask you a very simple question okay let's say you close your eyes and someone Taps your wrist are you able to fill it yes but if you close your eyes and an ant a small little ant very tiny ant by the way is just walking on your wrist are you able to feel the end you know walking on your wrist the answer is probably not how is that possible because the antt is stepping on your skin so it's a stimulus but why aren't you able to feel it so to answer this question now some students will say well the wrist is a the tapping on the wrist is a strong stimulus and the tiny and walking on the wrist is a weak stimulus so that's it and of course you will be right okay a strong stimulus is able to depolarize the axon which creates a membrane potential of positive 30 MTS and therefore this generates an action potential and therefore the action potential is sent to the brain and then your brain says hey someone is tapping on your wrist that's fine but for the ant however yes it's stimulating your skin but the membrane did not successfully depolarize so it did not generate an action potential so were there any signals sent to the brain no there were no signals sent to the brain in this case so you did not feel the antt on your skin now immediately I'll ask my students the question is this a good or bad thing some students will say it's bad because we want to feel everything but some students will say no it's good because you know a tiny antt walking on your skin is not an ex extremely important stimulus so it's good to not generate action potential sometimes because it in this case you can save ATP you you conserve more ATP in that case you don't want to be able to detect everything for example imagine if you sleeping and a small little insect just crawled on your leg do you want to wake up from that no you don't okay the body has to go through this period where like it has to notice that some stimulus are just not so important to generate the action potential so the question is how does the body do this how does the body control what stimulus generates Action potentials and what stimulus don't so this is where we have to talk about something called the threshold potential as you can see over here I'm just drawing out the axon and the green color dots are just for example the sodium ion channels okay yes I know I know I usually represent I'm supposed to represent the sodium ion channels as Orange color but let's just call it green color in this case I made a slight mistake so remember when it's maintaining a resting membrane potential there is a low sodium ion concentration inside the axon and a higher sodium ion concentration outside the axon this will maintain the resting membrane potential of about -70 Ms now for example a weak stimulus is inflicted upon the skin the receptor and this week stimulus over here I just want you to see what happens to the voltage gated sodium ion channels look at how many voltage gated sodium ion channels open over there only one voltage gated sodium ion Channel opens in this case so you might be thinking oh that's a good thing okay yes but will a lot of sodium ions actually rush into the axon not exactly yes some sodium ions go into the axon but not a lot so in this case over here some sodium ions very few sodium ion channels open in this case just one and even though sodium ion rushes into the cell yes it starts to become more positive that is true the voltage the membrane potential starts to go up but it's not able to hit about 55 MTS 55 MTS is the threshold potential or the limit that must be hit before it generates the action potential if the axon cannot hit 55 MTS therefore it will not be able to generate an ex potential at all so if there's no action potential generated will it send a signal to your brain no it won't okay so that is why a weak stimulus cannot generate an action potential because the stimulus is not strong enough to reach the threshold potential okay so conversely imagine if the in the case of a strong stimulus however now in the strong stimulus someone Taps on your wrist now that stimulus is quite strong in that case when the strong stimulus happen see the difference earlier because of the weak stimulus only one sodium ion Channel open or very few sodium ion channels open but when someone Taps on your wrist in this case over here there is a higher amount of sodium ion channels that open earlier was one but now is three so more sodium ions are able to rush into the cell the membrane potential starts to become more positive and guess what as it starts to go up as more sodium ion rushes into the cell the axon it is able to reach the threshold potential and because it reaches the threshold potential this is where more sodium ion channels will basically open and when more sodium ion channels open more sodium ion rushes in which causes the membrane to reach positive 30 m volts and successfully depolarize and when the membrane successfully depolarizes to positive 30 MS that's when an action potential is generated and this is when it's able to send the signal all the way for example to the brain and then your brain tells you that hey someone is tapping on your wrist so this is how it works so this is a good thing because like I said you do not want to be able to generate Action potentials for everything so for example when the tiny little insect is just crawling on your skin um the stimulus is so weak that it depolarizes the membrane slightly yes but it's not able to reach the threshold potential this is good because you do not want to unnecessarily send less important signals to the brain so because sending impulses to the brain or to your central nervous system requires a lot of ATP so the nervous system do not want to commit to it if the stimulus is very weak so by having something called the threshold potential our body is able to conserve ATP and only send impulses when necessary