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6) The falling phase of the action potential is due mainly to A) Na+ flow in the cell only. B) Na+ flow out of the cell only. C) K+ flow out of the cell only. D) K+ flow into the cell only. E) Na+ flow out of the cell and K+ flow into the cell. 7) Calcium is important in the synapse because it A) is necessary for acetylcholine synthesis. B) signals the exocytosis of the neurotransmitter. C) binds to receptors on the postsynaptic cell, opening ion channels, and triggering grade potentials. D) leaves the axon terminal, hyperpolarizing the cell. 8) The resting membrane potential results from A) uneven distribution of ions across the cell membrane only. B) differences in membrane permeability to ions only. C) activity of the sodium/potassium pump only. D) uneven distribution of ions across the cell membrane and differences in membrane permeability to ions. E) None of the answers are correct. 9) When comparing action potentials to graded potentials, you should remember that A) graded potentials can undergo summation. B) action potentials can undergo summation. C) that the rate of action potentials is limited by the refractory period. D) graded potentials can undergo summation and the rate of action potentials is limited by the refractory period. E) action potentials can undergo summation and the rate of action potentials is limited by the refractory period. 10) All of the following must occur before a second action potential can begin, EXCEPT A) the Na+ and K+ ions that moved in/out of the cell must move back to their original compartments. B) the Na+ inactivation gate must open and the Na+ activation gate must close. C) the absolute refractory period must occur. D) the Na+ and K+ ions that moved in/out of the cell must move back to their original compartments; the Na+ inactivation gate must open; and the Na+ activation gate must close. E) None of the answers are correct.

          6) The falling phase of the action potential is due mainly to
A) Na+ flow in the cell only.
B) Na+ flow out of the cell only.
C) K+ flow out of the cell only.
D) K+ flow into the cell only.
E) Na+ flow out of the cell and K+ flow into the cell.

7) Calcium is important in the synapse because it
A) is necessary for acetylcholine synthesis.
B) signals the exocytosis of the neurotransmitter.
C) binds to receptors on the postsynaptic cell, opening ion channels, and triggering grade potentials.
D) leaves the axon terminal, hyperpolarizing the cell.

8) The resting membrane potential results from
A) uneven distribution of ions across the cell membrane only.
B) differences in membrane permeability to ions only.
C) activity of the sodium/potassium pump only.
D) uneven distribution of ions across the cell membrane and differences in membrane permeability to ions.
E) None of the answers are correct.

9) When comparing action potentials to graded potentials, you should remember that
A) graded potentials can undergo summation.
B) action potentials can undergo summation.
C) that the rate of action potentials is limited by the refractory period.
D) graded potentials can undergo summation and the rate of action potentials is limited by the refractory period.
E) action potentials can undergo summation and the rate of action potentials is limited by the refractory period.

10) All of the following must occur before a second action potential can begin, EXCEPT
A) the Na+ and K+ ions that moved in/out of the cell must move back to their original compartments.
B) the Na+ inactivation gate must open and the Na+ activation gate must close.
C) the absolute refractory period must occur.
D) the Na+ and K+ ions that moved in/out of the cell must move back to their original compartments; the Na+ inactivation gate must open; and the Na+ activation gate must close.
E) None of the answers are correct.

$6) The falling phase of the action potential is due mainly to A) Na+ flow in the cell only. B) Na+ flow out of the cell only. C) K+ flow out of the cell only. D) K+ flow into the cell only. E) Na+ flow out of the cell and K+ flow into the cell. 7) Calcium is important in the synapse because it A) is necessary for acetylcholine synthesis. B) signals the exocytosis of the neurotransmitter. C) binds to receptors on the postsynaptic cell, opening ion channels, and triggering grade potentials. D) leaves the axon terminal, hyperpolarizing the cell. 8) The resting membrane potential results from A) uneven distribution of ions across the cell membrane only. B) differences in membrane permeability to ions only. C) activity of the sodium/potassium pump only. D) uneven distribution of ions across the cell membrane and differences in membrane permeability to ions. E) None of the answers are correct. 9) When comparing action potentials to graded potentials, you should remember that A) graded potentials can undergo summation. B) action potentials can undergo summation. C) that the rate of action potentials is limited by the refractory period. D) graded potentials can undergo summation and the rate of action potentials is limited by the refractory period. E) action potentials can undergo summation and the rate of action potentials is limited by the refractory period. 10) All of the following must occur before a second action potential can begin, EXCEPT A) the Na+ and K+ ions that moved in/out of the cell must move back to their original compartments. B) the Na+ inactivation gate must open and the Na+ activation gate must close. C) the absolute refractory period must occur. D) the Na+ and K+ ions that moved in/out of the cell must move back to their original compartments; the Na+ inactivation gate must open; and the Na+ activation gate must close. E) None of the answers are correct.$

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