PNB 2274 Exam 2| questions and answers correct and verified A+

PNB 2274 Exam 2| questions and answers correct and verified A+ Why are cell membranes not conductive? - correct answers-cell membranes insulate the flow of electrical charge. How is the electrical potentials (membrane voltage) measured in a cell? - correct answers-Membrane voltage is always in terms of inside relative to outside: electrical potentials are measured using intracellular electrodes inside of cells with reference to an external ground electrode. At what point do we get a balance between diffusion and electrical charge? - correct answers-Nernst equilibrium - Eionx - the electrical potential/voltage at which the diffusional flow of an ion one way is balanced by the electrostatic attraction in the other. At equilibrium what is the voltage like of a membrane? - correct answers-at equilibrium there is a difference in charge What is the Nernst Equation? - correct answers-Eionx = RT/zF ([x]out/[x]in) What determines the membrane potential at which an ion is in equilibrium? - correct answers-the concentration gradient and the charge of the ion (transporters will serve to change concentration slightly and thus effect equilibrium potential) What are the only factors of the nernst equation that will change Ex of a particular ion? - correct answers-temperature and concentration What is the ln of 1? Why does this matter? - correct answers-the ln of 1 is zero - if the concentration of the particular ion on both sides of the membrane are equal, this part of the nernst equation equals one and therefore there is no net flow of the ion and Ex=0 - because we are considering only one ion, charge will be equal on both sides of the membrane - no conc. gradient or electrostatic gradient What is the ln of a number less than 1? Why does this matter? - correct answers-the ln of a number less than 1 is a negative number - this means that there is a greater concentration of the particular ion inside the cell than outside What is the ln of a number greater than 1? Why does this matter? - correct answers-the ln of a number greater than 1 is a positive number - this means that there is a greater concentration of the particular ion outside the cell than inside What are the Nernst values (Vm) for potassium, chloride, sodium, and calcium? - correct answers-Ek= -90 Ecl= -70 Ena= +60 Eca= +130 What are the relative concentrations of potassium, sodium, chloride? - correct answers-K+ is higher inside Na+ is higher outside Cl- is higher outside Why do we use the GHK equation? - correct answers-cell membranes are permeable to more than one ion at rest - the Vm therefore is a weighted average of the Ex for each permeable ion - "z" is now 1 - "P" is a measure of the permeability Why is the ratio for the permeability of chloride reversed? - correct answers-Cl is a negative ion What is the GHK equation like for a resting membrane? - correct answers-the permeability to sodium is zero in a resting membrane therefore Pna can be eliminated from the equation - only K+ and Cl- dictate the membrane potential at rest - this is why Vm at rest is close to Ek because the membrane is most permeable to potassium What is the role of K+ leak channels? - correct answers-K+ leak channels maintain the resting potential What are graded potentials and where are graded potentials important? - correct answers-graded potentials happen in the dendrites of neurons and the motor endplate of motor neurons - graded potentials are the input coming into dendrites and can be depolarizing or hyperpolarizing - decrease in strength as they spread out from the point of origin (decrement) = decrease in strength of EPSP - can be involved in temporal summation and spatial summation - dictated by ligand gated channels What is the definition of an action potential? Where does an action potential occur? - correct answers-an action potential occurs in the axons - are all-or-nothing (must reach threshold membrane potential to have an action potential) - muscle contractions and the release of hormones are examples of action potentials - dictated by voltage gated channels What are the differences between depolarization, repolarization, and hyperpolarization? - correct answers-depolarization: changing membrane potential to be more positive (opening of Na+ channels) repolarization: returning membrane potential towards rest potential (K+ channels open) hyper polarization: changing membrane potential to be more negative (K+ channels are remaining open longer than sodium channels which close quickly) What is temporal summation? - correct answers-two sub-threshold graded potentials will NOT initiate an action potential if they are far apart in time two sub threshold potentials arrive at trigger zone in a short period of time sum to initiate an action potential What is spatial summation? - correct answers-summation of several sub threshold signals results in an action potential - Postsynaptic Inhibition = an inhibitory presynaptic neuron prevents an action potential from firing (IPSP outweighs the EPSPs) There are 9 Steps involved in an action potential sequence: - correct answers-1. resting potential membrane 2. depolarizing stimulus 3. membrane depolarizes to threshold - voltage gated sodium channels open quickly and sodium influx - voltage gated potassium channels open slowly and potassium efflux 4. rapid sodium entry depolarizes cell 5. sodium channels close and slower potassium channels are opening 6. potassium moves from cell to extracellular fluid 7. potassium channels remain open an additional potassium leaves the cell resulting in hyperpolarizing cell 8. voltage gated potassium channels close and less K+ leaks out of cell 9. cell returns to its resting ion permeability and resting membrane potential What is the effect of depolarization on voltage gated channels? - correct answers-depolarization "activates" voltage gated ion channels (activates=opens) What is the effect of hyperpolarization and repolarization on voltage gated channels? - correct answers-hyperpolarization and repolarization "de-activates" voltage gated channels (deactivates = closes) What are the effects of depolarization and hyperpolarization/repolarization on blocking voltage gated sodium channels? - correct answers-depolarization will "inactivate" voltage gated sodium channels and hyperpolarization/repolarization will un-inactivate (unblock) voltage gated sodium channels. What is the difference in timing/speed of activation and inactivation of sodium and potassium channels? - correct answers-voltage gated sodium channels will activate and deactivate quickly and inactivate and un-inactivate slowly voltage gated potassium channels activate and deactivate slowly (no blocker for these ion channels) What type of feedback loop are sodium channels and why? - correct answers-sodium channels are a positive feedback loop - open via depolarization causing influx of sodium that then results in greater depolarization and more sodium channels opening What happens at the peak of an action potential graph in regards to sodium channels? - correct answers-the membrane potential is very positive and repels ions causing the efflux of potassium ions - during repolarization potassium channels are very activated What type of feedback loop are the potassium channels and why? - correct answers-potassium channels are on a negative feedback loop - potassium channel