Value of the transmembrane voltage

1. A sea urchin egg is used in a voltage clamp experiment; that is, the value of the transmembrane voltage is set by the experimenter, not by the properties of the membrane.
The transmembrane voltage is held at +10 mV for one minute. At the end of that time
A. the voltage-gated calcium channels are all open.
B. the voltage-gated calcium channels are all inactivated.
C. the voltage-gated calcium channels have recovered from inactivation.
D. the voltage-gated calcium channels are going through cycles of opening and inactivation as the
cell generates repetitive action potentials.
E. any of answer A though D above could occur, depending on the density of potassium channels.

2. In a calcium action potential
A. the influx of calcium ions depolarizes the plasma membrane.
B. depolarization of the plasma membrane opens voltage-gated calcium channels.
C. open voltage-gated calcium channels carry an inward current of calcium ions.
D. an inward current of calcium ions aIDs positive charge to the cytosol.
E. all of the above occur.

3. Action potentials in nerve cell axons last a much shorter time than action potentials in
sea urchin eggs because
A. sodium has only a single positive charge while calcium has two.
B. voltage-gated sodium channels are found only at the nodes, while voltage-gated calcium channels
are found over the entire surface of the egg cell.
C. sodium ions are removed rapidly from the cytosol by the Na+/K+ ATPase.
D. voltage-gated sodium channels inactivate more rapidly than do voltage-gated calcium channels.
E. calcium has a higher atomic weight than does sodium and therefore diffuses more slowly.

4. An action potential is being generated at the node of a myelinated axon. Which of the
following statements is false?
A. Sodium is entering the axon interior through voltage-gated sodium channels.
B. Potassium is leaving the axon interior through potassium channels.
C. Calcium is entering the axon interior through voltage-gated calcium channels.
D. A net inward current is flowing across the plasma membrane of the node.
E. Current is leaving the region of the node axially, through the cytosol of the nerve cell.

5. The nodes of a myelinated axon are spaced a distance apart of approximately
A. 1 nm.
B. 1 ?m.
C. 1 mm.
D. 1 cm.
E. 1 m.

6. A sperm can trigger an action potential in a sea urchin egg because
A. its cytosol contains a lot of calcium ions that, upon fertilization, rush into the egg.
B. its membrane contains ion channels that, upon fertilization, pass an inward current that depolarizes
the egg plasma membrane.
C. its membrane contains ion channels that, upon fertilization, pass an outward current that repolarizes
the egg plasma membrane.
D. its cytosol contains a chemical that tends to pop the voltage-gated calcium channels into an
open state.
E. its cytosol contains a protease that modifies the behavior of voltage-gated calcium channels in
the plasma membrane of the egg.

7. When a nerve cell axon is depolarized to threshold, the flow of potassium through
potassium channels in the plasma membrane is
A. outward, and of a greater absolute amplitude than at the resting voltage.
B. inward, and of a greater absolute amplitude than at the resting voltage.
C. outward, but of a smaller absolute amplitude than at the resting voltage.
D. inward, but of a smaller absolute amplitude than at the resting voltage.
E. zero.

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