02 11 2015 Exam 4 Measure of voltage gradient Difference from inside the cell to somewhere outside the cell Gradient a cross the membrane what is happening from the one side to the other Vm voltage across membrane that equals our membrane potential o At rest most cells Vm 70 mV little negative on inside outlet is standard of 120 Volts so SMALL charge here o Due to all charge components FIGURE 6 8 Vm sum of Ex of all ions Ex equilibrium potential Vm Ena Ek Ecl Eca2 osmolarity will change as result eq potential will change V at which electron and concentration Gs for a component are balanced Alter PM permeability FIGURE 6 15 ligand gated channel Increase perm ions move biggest impact change Vm graded potential o When we change membrane potential graded potential Whether were going 70 to 60 or 70 to 80 diffusing through distance problem ex window open near feel cold air in hot room but as move away from window going to feel no change and still warm local changes of when we change the permeability near to where we are less further away to where we get points on our membrane that doesn t change local change in ion flow small points on a membrane where we are doing this on a cell could have voltage or mechanically gated channels besides ligand change in Vm isn t going to effect mechanically gated channels Voltage gated channel change charge when we get right Vm our voltage channels may open up Graded Potentials GPs o Terms changes from rest equates to steady state 70mV aka polarized o Cells at rest are polarized o start of with polarized cell o mV units of measurement representation of membrane potential Vm o depolarized less negative stimulus become less polarized b c 0 no polarization decreased polarization MAKE cell less polarized stimulatory stimulus KEY when depolarize we stimulate cell o hyperpolarized more polarized then when its at rest more negative inhibitory stimulus o repolarization to rest returning to polarization FIGURE 6 14 o be able to tell which is which based on chart graph in general FIGURE 6 16 o Characteristics cells regular mechanisms take it back to 70 back to steady state resting point stronger stimulus increase size so signal bigger change in Vm Bigger distance decrease size so signa As go further away from stimulus response by the cell goes down PROBLEM Have to find some other way to work with electrical things that aren t based on graded potential o What if GP occurs near V gated channels IF we get right Vm around V gated channels can open Action Potentials APs o In excitable cells GP can cause Quick large changes in Vm FIGURE 6 19 when we get right GP in special cells nearby neurons are one of these special cells All or nothing event not like GP where there is more variability Either looks like this or nothing at all EX pregnancy either pregnant or not cannot be in between Components needed Graded potential near voltage gated channels 1 Voltage gated Na channels with inactivator FIGURE 6 19 2 Voltage gated K channels About very specific type of ordering or activation closing components of these channels stereotyped movement of these NA and K why does graph 6 19 look like this and no other way Need to talk about 3 most difficult things we will discuss this semester events of an AP Events of an AP o 1 start off with membrane at rest 70mV closed at rest somehow want to stimulate change Vm to create a graded potential o 2 Local D reaches threshold potential TP Vm that instantly opens up our v gated Na channels also Vm that gets the opening started for our K channel need to move at different rates Na goes in when channel is opens o 3 Na influx of plus charges which is gonna become a small negative number more D depolarization caused us to depolarize EXAMPLE of positive feedback positive feedback keeps going up and up in wrong way need to do something opening process inactivates o 4 Na channels inactivated have NOT closed them still open K channels open its gonna move through EX open garage door with opener to pull in car but husbands car is there so cant pull car in THEREFORE Na can channels can open but cannot go into cell b c inactivated Potassium is going to want to move from high to low so conc gradient says go out BUT need to pay attention to electrical gradient o 5 K outflux VM is going to be lowered back down again repolarizing the cell returning it towards 70mV Na channels close going to take time threshold is determining above its Na is open below it Na is closed instantaneous o 6 Cell Hyperpolarizing since K slow to close go past our resting point o 7 K channels close negative feedback return to rest o Threshold potential TP Vm req d to activate Na stimulus then generated by Na channels influx weak depolarization s sub threshold potentials FIGURE 6 21 ex egg needing sperm WEDNESDAY 2 12 notes here 02 11 2015 02 11 2015
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