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 Action Potentials Threshold potential TP Figure 6 21 Vm required to activate Na channels Stimulus then generated by Na influx Weak depolarizations subthreshold potentials AP amplitude aka size if occur Independent of stimulus o The amplitude will always be the same and doesn t depend on how strong or weak the signal is The bullet in a gun will always go the same distance no matter how hard or weak you pull the trigger No change in size not equal to GP Practical application Local anesthetics many block Na channels Propagation down axon Figure 6 23 Adjacent sections of plasma membrane PM o Has action potential but CANNOT move o One starts the next one o Action potential height will ALWAYS be the same height size As distance increases no change in size So no signal changed No distance problem Each action potentials takes 1 2 milliseconds o Unidirectional Not going to trigger backwards Necessary for speed Due to 1 Hyperpolarization Going to need a bigger stimulus to reach the threshold backward whereas going to need a smaller not as big stimulus to reach the threshold forward so it s easier to go keep going forward than go backwards 2 Na channel blocked Propagation down axon Figure 6 24 Myelin insulator o Aids graded potentials GP Usually has a big drop off and decreases quickly but with myelin the drop off is not as large and doesn t decrease as quickly o Blocks action potentials AP Increases conduction velocity Myelin covers some of the section of plasma membrane and makes the action potential move VERY fast Action potentials are triggered and then moves over their graded potentials and continues to trigger the next action potentials o Action potentials AP only at nodes of Ranvier o
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