c. absolute refractory period
d. resting membrane potential
92. A membrane produces an action potential whenever the potential across it reaches what level?
a. the resting potential
b. -90 mV
*c. the threshold of excitation
d. the refractory period
93. Nettie is in the laboratory working with cultured neurons. She wants to record the voltage following the opening of the sodium channels. What does she need to do to get the sodium channels to open?
*a. Add a solution that will result in depolarizing the membrane.
b. Add a solution that will result in hyperpolarizing the membrane.
c. Increase the amount of sodium outside of the neuron.
d. Produce an action potential and get to the refractory periods.
94. What occurs when depolarization is less than the cell’s threshold?
a. Sodium is prevented from crossing the membrane.
b. Potassium is prevented from crossing the membrane.
*c. Sodium crosses the membrane only slightly more than usual.
d. The cell will still produce an action potential.
95. Which action would depolarize a neuron?
a. Decreasing membrane permeability to calcium
b. Increasing membrane permeability to potassium
c. Decreasing membrane permeability to sodium
*d. Increasing membrane permeability to sodium
96. The action potential of a neuron depends mostly on what movement of ions?
*a. Sodium ions entering the cell
b. Sodium ions leaving the cell
c. Potassium ions entering the cell
d. Potassium ions leaving the cell
97. Zandra is studying about the ions involved in the action potential. She records in her notes that ____.
*a. the concentration of sodium remains more concentrated outside the neuron than inside even during an action potential
b. the concentration of potassium remains more concentrated outside the neuron than inside even during an action potential
c. the concentration of sodium and potassium equalize across the membrane during an action potential
d. during an action potential, the sodium channels stay open for a long period of time
98. Voltage-activated channels are channels for which a change in the voltage across the membrane alters their ____.
*a. permeability
b. length
c. number
d. threshold
99. At the peak of the action potential, the electrical gradient of potassium ____.
a. is the same as during the resting potential
b. pulls sodium into the cell
*c. pushes potassium out of the cell
d. pulls potassium into the cell
100. When the potential across a membrane reaches threshold, the sodium channels ____.
*a. open to let sodium enter the cell rapidly
b. close to prevent sodium from entering the cell
c. open to let sodium exit the cell rapidly
d. close to prevent sodium from exiting the cell
101. A drug that blocks the sodium gates of a neuron's membrane will ____.
a. decrease the threshold
*b. block the action potential
c. cause repeated action potentials
d. eliminate the refractory period
102. After the peak of an action potential, what prevents sodium ions from continuing to enter the cell?
a. There is no longer a concentration gradient for sodium.
b. The sodium-potassium pump greatly increases its rate of activity.
c. All the available sodium ions have already entered the cell.
*d. The sodium gates in the membrane close.
103. Mae is studying for an exam on the action potential. She writes in her notes that the sodium channel closes ______.
a. when the electrical gradient for sodium is eliminated
*b. after the neuron reaches threshold
c. at the peak of the action potential
d. as a result of the refractory periods
104. What causes potassium ions to leave the axon just after the peak of the action potential?
*a. A continuing concentration gradient and the opening of the potassium gates
b. An increase in the concentration gradient across the membrane
c. An increased tendency of the sodium-potassium pump to push potassium out
d. Binding of potassium ions to proteins that leave at this time
105. A drug will prevent an action potential if it ____.
a. lowers the threshold of the membrane
b. blocks the movement of potassium across the membrane
*c. blocks the movement of sodium across the membrane
d. increases the movement of sodium across the membrane