increasing extracellular k+ concentration will cause depolarisation. reason : normally the RMP is close to equilibrium potential of k+ as it has maximum permeability. also the equilibrium potential depends on ratio of K+ inside to K+ outside {from Nernst eqn} so, if the outside concentration increases , the ratio will tend to 1. from nernst eqn now it's evident that the value of emf( equilibrium potential of k+) will lie somewhere between -61 to 0 depending upon how much outside concentration is inceased. ie the RMP will increase towards 0 mV
So in hypokalemia is hyperpolarisation seen........ Also mam in sympathetic situvation artrioles constrict by alpha 1 so TPR increase ..if TPR increase heart will find difficult to pump blood as diastolic bp will be high around 90 ...how this kind of action is usefull in emergency situvation flight fright.....i.e why do we want to maintain diastolic bp and its importance...
Depolarization As Depolarization indicates influx of Na+ions And hyperpolarization means extra efflux of K+ ions from cell but here the conc. Of K+ is more in ECF so hyperpolarization will not be suitable answer Am I right mam?🙂
Since there is increased extracellular concentration of potassium, there is a decrease in the concentration gradient of potassium from inside to outside, so the duration of the repolarization will be increased, altogether increase in the duration of action potential, thereby increasing the chance of arrhythmias due to early afterdepolarization.
@@PhysiologyOpen thank you physiology open. Hope this kinds of questions at the end of a video lecture is useful ,this make us think ,and even if we are wrong. .we will wait patiently for the next video to get the correct explanation
@@PhysiologyOpen Ha Ha. I was half asleep when I answered your question. I just read your question. what happened if increased extracelluar K+?... Increased K+ concentration extracelluar, which will work against the "leaking out" K+ from intracelluar to extracelluar, therefore, the membrance potential becomes less negative, it will make the membrane easier to depolarize. Here is the POINT. The "positive" change of membrane potential has to reach the "threshold" before it can depolarize/discharge. so, your answer "depolarization" is not an acurate one either. I can give you a clinical example, slightly elevating blood k+ will not make heart "Jittery" . the blood K+ level has to reach the neighborhood of "6.5mEq/L", which, then, will cause a widened QRS wave on ECG because the phase 0 of action potential decreases, leading to a longer action potential -- widened QRS. the nomal K+ level 3.6-5.2 mmol/L. Hyperkalemia can be life threatening, I will treat it way before it reaches level of 6.5 .. Thanks for your lecture. It is by far very detailed and informing.
Absolutely correct. Thank you for giving a detailed explanation. I think this will be beneficial for other people too. Only one think I will like to add...depolarization is any change in potential towards positive. It may or may not reach threshold. So increased extracellular potassium will cause depolarization i.e resting membrane potential which is less negative. This makes the tissues more excitable. And in case of effect on action potential, it will increase the duration of action potential. Then this effect of K+ on RMP can be easily understood by putting the changed vaues in Nernst Equation. Thanks again
@@醫療無疆界 Calcium will not have any effect on nerve and skeletal muscle action potential directly. However, decrease in extracellular calcium levels increases the probability of opening of sodium channels and hence making the membrane more excitable. In nodal cardiac tissue, there will be some increase in amplitude of action potential. However the main effect of increased extracellular calcium is on mechanical activity i.e contraction of heart rather than on action potential
