Which of the following statements regarding action potentials generated in a neuronal membrane is FALSE?
A. Action potentials travel decrementally down the membrane.
B. An action potential generates a new action potential in an adjacent area of membrane.
C. An action potential generates a local current that depolarizes adjacent membrane to threshold potential.
D. Action potentials are usually initiated at the initial segment of a neuron.
E. An action potential generated by a threshold stimulus is the same size as one generated by a supra-threshold stimulus.
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Question 2) Neuronal axons typically have abundant
A. voltage-gated channels for Na+ that open in response to depolarization.
B. voltage-gated channels for K+ that open in response to hyperpolarization.
C. ligand-gated channels for Na+.
D. ligand-gated channels for K+.
E. voltage-gated channels for Ca2+.
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Question 3) Which is most directly responsible for the falling (repolarizing) phase of the action potential?
A. Voltage-gated Na+ channels are opened.
B. The Na+, K+ pump restores the ions to their original locations inside and outside of the cell.
C. The permeability to Na+ increases greatly.
D. ATPase destroys the energy supply that was maintaining the action potential at its peak.
E. The permeability to K+ increases greatly while that to Na+ decreases.
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Question 4) Which of the following statements about the refractory period of a membrane is TRUE?
A. The absolute refractory period refers to the period of time during which another action potential cannot be initiated in that part of the membrane that is undergoing an action potential, no matter how great the strength of the stimulus.
B. The relative refractory period refers to the period of time during which another action potential can be initiated in that part of the membrane that has just undergone an action potential if a stronger than normal stimulus is applied.
C. The refractory period prevents the action potential from spreading back over the part of the membrane that just underwent an action potential.
D. The refractory period places an upper limit on the frequency with which a nerve cell can conduct action potentials.
E. All of the above choices are correct.
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Question 5) Which of the following statements about the phases of a neuronal action potential is TRUE?
A. During the after-hyperpolarization phase, the permeability of the membrane to sodium ions is greater than its permeability to potassium ions.
B. During the after-hyperpolarization phase, the permeability of the membrane to potassium ions is greater than its permeability at rest.
C. During the repolarizing phase, the permeability of the membrane to sodium ions is greater than its permeability to potassium ions.
D. Potassium channels inactivate during the depolarization phase.
E. Repolarizing to negative membrane potentials causes the sodium channels to inactivate.
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Question 6) Why are action potentials sometimes described as being all-or-none in character?
A. The rate of propagation of an action potential down an axon is independent of stimulus strength.
B. They are associated with an absolute refractory period.
C. A supra-threshold stimulus is required to stimulate an action potential during the relative refractory period.
D. An action potential occurs whenever a suprathreshold stimulus occurs, and its amplitude does not vary with the size of a stimulus, as long as the membrane is not in the refractory period.
E. Action potentials are always the same size, even when ion gradients vary in size.
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Question 7) Which is TRUE about neuronal membrane electrical and concentration gradients at the peak of the action potential?
A. The electrical gradient is in a direction that would tend to move K+ out of the cell.
B. The concentration gradient for K+ is in a direction that would tend to move it into the cell.
C. The concentration gradient for K+ greatly increases compared to at rest.
D. The concentration gradient for Na+ is in a direction that would tend to move it out of the cell.
E. The electrical gradient for Na+ is in a direction that would tend to move it into the cell.
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Question 8) Which describes the response of the voltage-gated channels when an axon is stimulated to threshold?
A. K+ channels open before the Na+ channels.
B. Na+ channels are activated and then inactivated.
C. K+ channels open at the same time as the Na+ channels.
D. K+ channels are opened when Na+ binds to the channel.
E. K+ influx causes Na+ channels to inactivate.
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Question 9) During the rising (depolarizing) phase of a neuronal action potential,
A. PK+ becomes much greater than PNa+.
B. PNa+ becomes much greater than PK+.
C. PK+ is the same as PNa+.
D. Na+ efflux (flow out of the cell) occurs.
E. K+ flows rapidly into the cell.
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Question 10) Which is NOT an example of a graded potential?
A. a receptor potential in a sensory receptor cell
B. a depolarizing excitatory postsynaptic potential (EPSP)
C. a hyperpolarizing inhibitory postsynaptic potential (IPSP)
D. a depolarizing pacemaker potential
E. a depolarizing action potential
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