10. ELECTRIC ORGANS
481
control the several million electrocytes. Similar but less extreme pyramids
of numbers are found in other electric fish. This aspect of neural organization may be denoted the committee principle. This term is chosen
in analogy with decision making by committees which tends to be more
rapid the smaller the committee.
One might question whether there could be a command ‘‘nucleus’’
containing a single cell, a committee of one. An example is provided
by the Mauthner cells of lower vertebrates which can be considered
single cell command systems for the axial musculature on either side
of the body (Furukawa and Furshpan, 1963; Diamond and Yasargil,
1969).
One could propose a number of reasons for the existence of control
systems containing more than one cell, such as protection against loss
of neurons and production of enzymes for maintenance of synaptic
transmission. At lower levels progressive increase in a number of neurons
may be equivalent to progressive increase in size. The two giant neurons
of the electric catfish are able to support a very small synaptic area
on a large number of electrocytes, but it seems likely that a large
number of neurons are required to provide the vast synaptic area in the
electric organs of Torpedo. Phylogenetic or ontogenetic factors may
also be responsible for the presence of the relays. Evolution may yet
progress to single-celled command “nuclei” although in most instances
the multicelled nuclei do about as well as required by the electric
organ.
It is interesting to compare the function of relay nuclei to transmission of impulses along an axon. At a node of Ranvier an impulse
that has been attenuated in electrotonic propagation from the preceding
node triggers the generation of a new impulse that is of full amplitude.
The node acts as a pulse restoring element, and decrementless conduction is thereby made possible. A relay nucleus potentially does more
than this. The volley of impulses in the fibers efferent from the relay
may be more synchronous than that in the afferent fibers, or all the
efferents may become excited when only a fraction of the afferents are
active (as appears to occur occasionally in Astroscopus) . These functions
do not require coupling of the cells; all that is necessary is that a
number of afferent fibers converge on each relay cell.
Although midline nuclei have developed in a number of control
systems, bilateral command nuclei may be fairly common because of
the basically bilateral organization of the nervous system. If either of
the two command nuclei can excite an entire effector system, synchronization between the two is not important. However, it would appear
functional for each command to reset the phase of firing in both com-
481
control the several million electrocytes. Similar but less extreme pyramids
of numbers are found in other electric fish. This aspect of neural organization may be denoted the committee principle. This term is chosen
in analogy with decision making by committees which tends to be more
rapid the smaller the committee.
One might question whether there could be a command ‘‘nucleus’’
containing a single cell, a committee of one. An example is provided
by the Mauthner cells of lower vertebrates which can be considered
single cell command systems for the axial musculature on either side
of the body (Furukawa and Furshpan, 1963; Diamond and Yasargil,
1969).
One could propose a number of reasons for the existence of control
systems containing more than one cell, such as protection against loss
of neurons and production of enzymes for maintenance of synaptic
transmission. At lower levels progressive increase in a number of neurons
may be equivalent to progressive increase in size. The two giant neurons
of the electric catfish are able to support a very small synaptic area
on a large number of electrocytes, but it seems likely that a large
number of neurons are required to provide the vast synaptic area in the
electric organs of Torpedo. Phylogenetic or ontogenetic factors may
also be responsible for the presence of the relays. Evolution may yet
progress to single-celled command “nuclei” although in most instances
the multicelled nuclei do about as well as required by the electric
organ.
It is interesting to compare the function of relay nuclei to transmission of impulses along an axon. At a node of Ranvier an impulse
that has been attenuated in electrotonic propagation from the preceding
node triggers the generation of a new impulse that is of full amplitude.
The node acts as a pulse restoring element, and decrementless conduction is thereby made possible. A relay nucleus potentially does more
than this. The volley of impulses in the fibers efferent from the relay
may be more synchronous than that in the afferent fibers, or all the
efferents may become excited when only a fraction of the afferents are
active (as appears to occur occasionally in Astroscopus) . These functions
do not require coupling of the cells; all that is necessary is that a
number of afferent fibers converge on each relay cell.
Although midline nuclei have developed in a number of control
systems, bilateral command nuclei may be fairly common because of
the basically bilateral organization of the nervous system. If either of
the two command nuclei can excite an entire effector system, synchronization between the two is not important. However, it would appear
functional for each command to reset the phase of firing in both com-