Action potential- threshold (Nervous system part 5)

this is Sarah Wilkinson from Humber College and the University of gu Humber in this video I'm going to continue talking about Action potentials and I'm going to specifically talk about what a threshold is I would encourage you to make sure you watch the video on action potentials before watching this one in that previous video I covered how resy member potential is negative and that when a stimulus occurs there's a rapid depolarization followed by repolarization now I wasn't entirely truthful in

that video sometimes a stimulus occurs and there's not a depolarization in this video I'm going to talk about the concept of threshold in the previous video I discussed how the resting membrane potential is negative there's more negative charges inside the cell than outside and that a stimulus will cause sodium channels to open up therefore sodium can move down its electrochemical gradient rendering the inside of the neuron more positive if a few sodium channels open up the inside of the neuron

becomes a little bit more positive what the threshold is is a value usually aroundus 55 Ms that will automatically cause an action potential to happen only if the membrane potential value reaches a certain threshold will depolarization occur if enough sodium channels open up the inside of the cell becomes slightly less negative or we we can also say more positive an action potential will occur this doesn't always happen sometimes only a few sodium channels open up so if the membrane potential d

oes not reach threshold not enough sodium channels open up no depolarization will occur and the action of sodium and potassium pumps will return the value the resting membrane potential back down to - 70 so here we call this a graded potential there was a slight increase in membrane potential but not enough to reach threshold so no action potential occurred sometimes a stimuli causes hyperpolarization this stimuli would open potassium channels only this way potassium will leave the neuron render

ing the inside more negative and this will make reaching threshold even harder so if any sodium channels open up we're going to see that we return back to resting and it's going to make it even harder to reach that threshold in following videos I'm going to talk about excitatory versus inhibitory neurotransmitters and sometimes the excitatory ones open sodium channels while the inhibitory ones open potassium channels so I encourage you to watch the video that I'm going to do on the synapse and w

e'll go into this further