Sodium channels open on this side only. Na* Na+ + V xX- AV cell |There is a net voltage across the cell. FIGURE P23.90
The voltage produced by a single nerve or muscle cell is quite small, but there are many species of fish that use multiple action potentials in series to produce significant voltages. The electric organs in these fish are composed of specialized disk-shaped cells called electrocytes. The cell at rest has the usual potential difference between the inside and the outside, but the net potential difference across the cell is zero. An electrocyte is connected to nerve fibers that initially trigger a depolarization in one side of the cell but not the other. For the very short time of this depolarization, there is a net potential difference across the cell, as shown. Stacks of these cells connected in series can produce a large total voltage. Each stack can produce a small current; for more total current, more stacks are needed, connected in parallel.
Electric eels live in fresh water. The torpedo ray is an electric fish that lives in salt water. The electrocytes in the ray are grouped differently than in the eel; each stack of electrocytes has fewer cells, but there are more stacks in parallel. Assuming that the electric eel and the torpedo ray are adapted to their environments, we can assume that
A. In the lower resistivity of salt water, it is adaptive for an electric fish to provide a higher output current at a lower output voltage.
B. In the lower resistivity of salt water, it is adaptive for an electric fish to provide a lower output current at a higher output voltage.
C. In the higher resistivity of salt water, it is adaptive for an electric fish to provide a higher output current at a lower output voltage.
D. In the higher resistivity of salt water, it is adaptive for an electric fish to provide a lower output current at a higher output voltage.
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