10+ Year Member
Jan 16, 2006
Don't have the answers to the following questions and would greatly appreciate it if someone could help me out with the correct answer choice. Want to be sure I am right or not. Thanks in advance!

1. Voltage-gated sodium channels
a. Are responsible for the repolarizing phase of the action potential
b. Are not present in skeletal muscle cells
c. Open in response to membrane hyperpolarization past threshold regardless of the
characteristics of that depolarization
d. Inactivate independently of how long the membrane remains depolarized

2. If the extracellular sodium ion concentration is lower than normal, the “overshoot”
aspect of a neuronal action potential (i.e., the rise above 0 PD) will be:
a. Less positive than normal
b. More positive than normal
c. Exactly the same as normal
d. It cannot be predicted
e. None of the above

3. Although possible, it is more difficult to elicit an action potential during the Relative
Refractory Period because:
a. A significant number of voltage-gated K channels are open
b. The threshold potential is more negative than it normally is
c. Compared to rest, the membrane potential is somewhat hyperpolarized and overall
membrane conductance is decreased
d. Compared to rest, the membrane potential is somewhat depolarized and overall
membrane conductance is decreased

4. The peak of the rising phase of a neuronal action potential is inside (P, positive; N,
negative) because of the activity of (V, voltage-gated; L, ligand-gated) channels selective
for (Na, sodium; K, potassium).
a. P,V,Na
b. N,L,K
c. P,L,Na
d. P,V,K
e. N,V,Na

5. Which of the following is most likely to be a contributing factor in the failure of action
potential propagation associated with demyelinating diseases?
a. Changes in the length of the absolute refractory period
b. Changes in the characteristics of Na channel inactivation
c. The distribution of Na and K channels along the length of the axon
d. Collapse of transmembrane Na and K gradients
e. Failure of the Na,K-ATPase
Jan 29, 2012
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