M. V. L. BENNE’IT
362
channels mediating different response components (see, especially, Hille,
1970; but also Bennett, 1961; Grundfest, 1966). Another argument for
separability of different components is the separate occurrence in
different cells and in macroscopically different regions of a single cell.
Electrocytes provide much of the comparative evidence of this kind.
A frequent characteristic of electrocytes is a kind of impedance
matching between the faces (Bennett, 1961). The lower the membrane
resistance the greater the electrical output of the cell, but also the greater
the leakage at rest, and the greater the exchange between Na’ and K+
across spike generating membrane during activity. It would thus be
inefficient to have one face of much lower resistance than the other (or
of much lower resistance than the series resistances of the external
medium and cytoplasm). One finds that a low resistance inexcitable face
generally is of lower resistance than the opposed, excitable face at rest
(Fig. 4A,C). The excitable face reduces its resistance during activity so
that under these conditions the resistances of the two faces are more
closely matched. In electrocytes where both faces become active and
decrease their resistances, the resting resistances are more or less equal.
Often this kind of impedance matching has morphological correlates,
which will be discussed in respect to individual cases and in Section 11, F.
C. Marine Electric Fish
There are three groups of marine fish possessing electric organs, the
torpedinids (electric rays), the rajids (skates or rays), and members of
the teleost genus Astroscopus (one group of stargazers). Because of
functional similarities between the electric organs it is convenient to consider these three groups together, although other characteristics make
them the “lowest” and the ‘%ighest” fish possessing electric organs. The
electrocytes of Astroscopus, the torpedinids, and some of the rajids are
the simplest known. There is only the one response component in the
innervated face and no response in the uninnervated face.
1. Astroscopus
The electric stargazers are a small group of several species that occur
along the western coast of the North and South Atlantic. There may also
be a representative on the Pacific side of the Panamanian isthmus
(Dahlgren and Silvester, 1906). These fishes are unusual in being somewhat flattened dorsoventrally. Their eyes are located on the dorsal
surface of the head and look virtually straight upward, hence the name
stargazer. Their habit is to burrow into sand leaving only their eyes
362
channels mediating different response components (see, especially, Hille,
1970; but also Bennett, 1961; Grundfest, 1966). Another argument for
separability of different components is the separate occurrence in
different cells and in macroscopically different regions of a single cell.
Electrocytes provide much of the comparative evidence of this kind.
A frequent characteristic of electrocytes is a kind of impedance
matching between the faces (Bennett, 1961). The lower the membrane
resistance the greater the electrical output of the cell, but also the greater
the leakage at rest, and the greater the exchange between Na’ and K+
across spike generating membrane during activity. It would thus be
inefficient to have one face of much lower resistance than the other (or
of much lower resistance than the series resistances of the external
medium and cytoplasm). One finds that a low resistance inexcitable face
generally is of lower resistance than the opposed, excitable face at rest
(Fig. 4A,C). The excitable face reduces its resistance during activity so
that under these conditions the resistances of the two faces are more
closely matched. In electrocytes where both faces become active and
decrease their resistances, the resting resistances are more or less equal.
Often this kind of impedance matching has morphological correlates,
which will be discussed in respect to individual cases and in Section 11, F.
C. Marine Electric Fish
There are three groups of marine fish possessing electric organs, the
torpedinids (electric rays), the rajids (skates or rays), and members of
the teleost genus Astroscopus (one group of stargazers). Because of
functional similarities between the electric organs it is convenient to consider these three groups together, although other characteristics make
them the “lowest” and the ‘%ighest” fish possessing electric organs. The
electrocytes of Astroscopus, the torpedinids, and some of the rajids are
the simplest known. There is only the one response component in the
innervated face and no response in the uninnervated face.
1. Astroscopus
The electric stargazers are a small group of several species that occur
along the western coast of the North and South Atlantic. There may also
be a representative on the Pacific side of the Panamanian isthmus
(Dahlgren and Silvester, 1906). These fishes are unusual in being somewhat flattened dorsoventrally. Their eyes are located on the dorsal
surface of the head and look virtually straight upward, hence the name
stargazer. Their habit is to burrow into sand leaving only their eyes