BIO 203- Module 3

ASSUME a cell with: EK = -90 mV; ENa = 60 mV; ECa = 122 mV; ECL = -80 mV; and PK >> PNa If the Nernst potential for ENa in a cell was suddenly altered and to equal 0 mv, the membrane potential would become less negative. True/ False

False- No, the Em would become MORE negative since the ENa is becoming less positive

During an action potential, the largest increase in sodium permeability occurs at the peak of the action potential waveform. True/False

False- The rising phase

A cell contains 100 mM K+ and is surrounded by interstitial fluid containing 10 mM K+. The equilibrium potential for potassium is -58mV. What is the temperature of the cell, in degrees C? Enter your answer as a whole number. Do not use words or symbols.

20(292 K)

A cell containing 12 mM Na+ is surrounded by interstial fluid containing 120mM Na+. What is the equilibrium potential, in mV for Sodium? Assume a temperature of 37 degrees C.

61.5/62mV or 0.0615V(use 61)

Put the following steps in the process of graded potential-induced secretion of insulin from a beta cell in the endocrine pancreas. 1. membrane depolarization causes voltage-gated calcium channels to open 2. ligand-gated K+ channels close when bound to their ligands 3. a graded depolarization occurs 4. the concentration of ATP inside the cell increases 5. the permeability of the cell membrane to potassium decreases 6. an increase in intracellular calcium concentration triggers exocytosis of insulin 7. glucose enters the cell through the GLUT transporter using facilitated diffusion 8. cell metabolism increases

7, 8, 4, 2, 5, 3, 1, 6

An action potential in a particular cell has the same amplitude, same duration, and same shape every time. True/False

True

The extracellular and intracellular compartments are in osmotic equilibrium, but chemical and electrical disequilibrium. a) True b) False

True; this is because if the were to not be in osmotic equilibrium it would be constantly gaining and losing water while expanding and shriveling. However, a cell is in chemical and electrical disequilibrium because the resting membrane potential is -70V

Choose the correct answer. The equilibrium potential for an ion... a) Can be calculated using the Nernst equation. b) Can be calculated using the Goldman equation. c) Is the same as the membrane potential. d) does not depend on temperature.

a)

ASSUME a cell with: [Cl-]IN = 10 mM; [Cl-]OUT = 100 mM; 37 degrees C, and the cell membrane is permeable to Cl- (pick the correct statement): a) The Nernst potential for Cl- (ECl) would be -61 mV. b) The Nernst potential for Cl- (ECl) would be 61 mV. c) If the cell becomes less permeable to Cl-, the Nernst potential for Cl- (ECl) would become less negative. d) If the cell becomes impermeable to Cl-, the Nernst potential for Cl- (ECl) would become 0 mV.

a) d) would be correct if it said membrane potential

Typically at rest, K+ permeability is 50 times greater than Na+ permeability (i.e., b = 0.02) and Em = -70 mV. If b suddenly becomes equal to 20, what happens to Em? a) Em becomes +50 mV b) Em becomes 0 mV c) Em becomes -50 mV d) Em does not change

a) Na+ will now have a more direct effect in trying to bring the membrane potential to its own unique equilibrium potential because the Pka of Na+ has increased since b has increased (b= Pka Na+/Pka K+); depolarizing the cell

Which of the following is NOT characteristic of diffusion potentials? a. continue indefinitely without decrement b. result from simple diffusion of ions c. can be either positive or negative d. depend on concentration gradients of ions

a.

During the rapid depolarizing (rising) phase of a neuron's action potential, a. membrane depolarization opens voltage-gated Na+ channels open and Na+ enters cell. b. the action potential is just starting the relative refractory period. c. membrane potential (Vm) briefly reaches a potential more positive than Na+ equilibrium potential. d. Both a) and b) are correct, and c) is incorrect e. a), b) and c) are all correct

a. b. the peak of the action potential when Na+ v-gated channels are inactivated and K+ channels begin to open c. does not go above the equilibrium potential of ENa+ but the membrane potential does go more positively towards it

Assume a typical cell with a sodium equilibrium potential of +58 mV. If the concentration of sodium in the intracellular fluid increased from 12 mM to 25 mM, the sodium equilibrium potential would ... a. decrease (become less positive). b. increase (become more positive). c. become negative (less than 0 mV). d. not change.

a. because you are decreasing the concentration gradient and essentially the driving force of Na+ ions the sodium equilibrium potential will become less positive

Which of the following statement(s) are true with respect to graded potentials? Select all of the correct answers. a) A graded potential has a threshold b) Graded potential amplitudes decay over distances c) An action potential is required to generate a graded potential d) Graded potentials are not regenerative e) Graded potentials can summate in space and time f) Graded potential amplitude increases with stimulus strength

b) d) e) f)

Which of the following events during an action potential contribute to membrane potential repolarization (e.g., the falling phase of the action potential)? Choose all of the correct answers. a. Opening of the inactivation gate of the voltage-gated sodium channels b. Closing of the inactivation gate of the voltage-gated sodium channels c. Opening of the activation gate of the voltage-gated sodium channels d. Closing of the activation gate of the voltage-gated sodium channels e. Opening of the activation gate of the voltage-gated potassium channels f. Closing of the activation gate of the voltage-gated potassium channel

b, e

Which of the following does/do NOT contribute to the repolarization phase of the action potential? a) Closing of inactivation gates in voltage-gated Na+ channels b) Opening of voltage-gated K+ channels c) Opening of activation gates in voltage-gated Na+ channels d) Answers a) and b) are both correct and answer c) is incorrect. e) Answers a), b) and c) are all correct

c) does not; would mean that the Na+ channels are open then the cell would depolarize a) does b)does

Which of the following statements about the resting membrane potential is/are true? a. It is normally equal to zero volts. b. Na+ is the dominant ion and the membrane potential is close to the equilibrium potential for Na+. c. It results, in part, from the concentration gradients for Na+ and K+. d. Both a) and b) are correct, and c) is incorrect e. a), b) and c) are all correct

c. a. NO resting membrane potential equals to -70 V b. K+ is the dominant ion

Which of the following statements is/are true for both graded potentials and action potentials in a neuron? a) May be depolarizing or hyperpolarizing b) Depends on activation of voltage-gated channels c) May produce an action potential in a neighboring patch of membrane d) Answers a) and b) are both correct and answer c) is incorrect. e) Answers a), b) and c) are all correct

c. Action potential can propagate along an axon and graded potentials can also cause an action potential in a neighboring patch of membrane a) yes for graded potentials(can hyperpolarize) but action potentials are all or nothing (rising stage= depolarizing and falling stage= repolarizing) b) yes for graded potentials but action potentials depend on graded potentials

Assume a cell with EK = -81 mV, EK would become more negative if ... a. K+ concentration in the ICF decreased b. K+ concentration in the interstitial fluid increased c. K+ concentration in the ICF increased d. Both a) and b) are correct, and c) is incorrect e. a), b) and c) are all correct

c. K+ is trying to leave the cell( low ICF to high ECF) to make EK more negative you would want to increase the driving force/concentration gradient by increasing the high concentration in the ICF even more than the ECF

Equilibrium Potential: Which of the following statements is/are true? a)The equilibrium potential of a permeant ion is the membrane potential that exactly balances the force of diffusion of the ion. b)The equilibrium potential of a permeant ion is the membrane potential at which there is no net movement of the ion through transmembrane channel proteins. c) The equilibrium potential of a permeant ion increases if the membrane permeability of the ion increases. d) Answers a) and b) are both correct and answer c) is incorrect. e) Answers a), b) and c) are all correct

d

Which of the following statements about the equilibrium potential of an ion across a membrane is/are true? a. If the electrical potential across the membrane is equal to the equilibrium potential of an ion, there will be no net movement of the ion across the membrane. b. The equilibrium potential for a cation whose extracellular concentration is greater than its intracellular concentration will be positive. c. An increase in membrane permeability of an ion will cause the equilibrium potential of that ion to become more negative. d. Both a) and b) are correct, and c) is incorrect e. a), b) and c) are all correct

d a. no need for the ion to try to get the membrane potential to be like its equilibrium potential b. example is Na+ c. can be more positive depending on the ion and its equilibrium potential!!

Membrane Potentials: Which of the following statements is/are true? a)A neuronal action potential has the same amplitude, duration, and shape every time. b)Action potentials conduct in a membrane without decrement while graded potentials exhibit decreases in amplitude with distance traveled. c) A graded potential has a threshold. d) Answers a) and b) are both correct and answer c) is incorrect. e) Answers a), b) and c) are all correct

d. Graded potentials don't have thresholds, action potentials do that when a graded potential reaches that threshold an action potential will fire