An action potential in a neuronal membrane differs from a graded potential in that:
A. an action potential requires the opening of Ca2+ channels, whereas a graded potential does not.
B. an action potential is propagated without decrement, whereas a graded potential decrements with distance.
C. an action potential has a threshold, whereas a graded potential is an all-or-none phenomenon.
D. movement of Na+ and K+ across cell membranes mediate action potentials, while graded potentials do not involve movement of Na+ and K+.
E. action potentials vary in size with the size of a stimulus, while graded potentials do not.
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Question 2) A threshold stimulus applied to an excitable membrane is one that is just sufficient to:
A. trigger an excitatory postsynaptic potential.
B. cause a change in membrane potential.
C. trigger an action potential.
D. be conducted to the axon hillock.
E. depolarize a dendrite.
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Question 3) Which must happen in order for an action potential to begin?
A. The membrane potential must be at the Na+ equilibrium potential.
B. Na+ influx must exceed K+ efflux.
C. The membrane must be out of the relative refractory period.
D. Na+ channels must all be inactivated.
E. Multiple inhibitory postsynaptic potentials (IPSPs) must summate.
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Question 4) Which of the following statements concerning the permeability of a typical neuron membrane at rest is TRUE?
A. The permeability to Na+ is much greater than the permeability to K+.
B. All of the K+ channels in the membrane are open.
C. The voltage-gated Na+ channels are in the inactivated state.
D. Most of the voltage-gated Na+ channels are in the closed state.
E. There is equal permeability to Na+ and K+.
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Question 5) The equilibrium potential of K+ ions in nerve cells is about -90 mV. The membrane potential of typical nerve cells at rest is -70 mV. Therefore
A. Increasing the permeability of a resting neuronal membrane to K+ will make the membrane potential more negative inside with respect to outside.
B. In resting neurons, there is a net diffusion of K+ into the cell.
C. changing the resting membrane potential of a neuron to -80 mV would increase K+ diffusion rate out of the cell.
D. potassium is the only permanent ion at rest.
E. there must be another permanent ion with an equilibrium potential more negative than -90 mV.
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Question 6) Which is FALSE about the equilibrium potential of a given ion across a membrane?
A. It is a function of the concentration of that ion on both sides of the membrane.
B. It is the potential at which there is no net movement of that ion across the membrane.
C. It is the potential difference across the membrane at which an electric force favoring movement of the ion in one direction is equal in magnitude and opposite in direction to the diffusion force provided by the concentration difference of the ion across the membrane.
D. A permeable ion will move in the direction that will tend to bring the membrane potential toward that ion's equilibrium potential.
E. An anion that is in higher concentration inside the cell than outside the cell will have a negative eqilibrium potential.
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Question 7) Which of these would occur if the concentration of ATP were depleted in a typical nerve cell?
A. Resting membrane potential would become more negative.
B. Resting membrane potential would become less negative.
C. The concentration gradient for Na+ would remain the same.
D. The resting membrane potential would eventually become positive inside with respect to outside.
E. There would be no change in the resting membrane potential.
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Question 8) Which would result from an increase in the extracellular concentration of K+ above normal?
A. depolarization of resting nerve cells
B. hyperpolarization of resting nerve cells
C. The potassium equilibrium potential of nerve cells would become more negative.
D. The sodium equilibrium potential would become less positive.
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Question 9) The diffusion potential due to the concentration gradient for Na+ across a nerve cell membrane:
A. favors its movement into the cell at the resting membrane potential.
B. favors its movement out of the cell at the resting membrane potential.
C. is equal and opposite to the electrical potential acting on Na+ at the resting membrane potential.
D. Is in the same direction as the diffusion potential due to the concentration gradient for K+.
E. favors movement of Na+ in the opposite direction as the electrical potential acting on Na+ at the resting membrane potential.
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Question 10) The membrane potential of most neurons at rest is:
A. equal to the equilibrium potential for potassium.
B. equal to the equilibrium potential for sodium.
C. slightly more negative than the equilibrium potential of potassium ion.
D. more positive than the equilibrium potential for potassium.
E. more positive than the equilibrium potential for sodium.
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