266
J. DZAMOND
IX. The Functions of the Mauthner Cells
.
. . . . . 331
A. Swimming and Equilibration: Two Improbable Functions . 331
B. Directionality Sensing: An Error
. . . . . . 338
C. The Avoidance Reaction: A Genuine Function
. . . 338
D. The Functions of the Collateral Inhibition
. . . . 340
E. Functions in Different Species: Unanswered Questions . 343
References
. . . . . . . . . . . . . 344
I. INTRODUCTION
The discovery of the giant axons bearing his name dates from Mauthner’s study in 1859. However, the association of these paired axons in
the spinal cord of teleost fish and certain amphibians with two remarkable cells in the brain (cells which were first described by Mayser in
1881) was only established later (Goronowitsch, 1888). These two cells
are fairly clearly related to certain brain nuclei, and especially to the
VIIIth cranial nerves; their possible function is usually discussed primarily
in that context. The earliest and certainly one of the most detailed and
interesting examplcs of such discussion can be found in the paper by
Bartelmez ( 1915). Moreover, because of their distinctive shape and
synaptic morphology as seen by light microscopy, the name Mauthner
cell has become associated largely with the soma-dendritic complex
in the medulla oblongata. The traditional approach, therefore, has tended
to relcgate the massivc spinal component of the Mauthner neuron to the
“nonintegrative” role of simply relaying information from the brain to
spinal motoneurons, which then drive the body muscles. This simplified
view is misleading. We shall see how the characteristics of the particular
spinal circuitry of which the Mauthner neurons are a part might well
define the limits of probable functions of these cells. The richness of
the neural inputs to, and intcrconnections between, the two Mauthner
neurons in the brain is remarkable and intriguing; it has, however, to be
interpreted with close regard to the findings in the spinal cord. Only
then can a satisfactory estimation of the total functions of what we
may call the Mauthner cell system be made.
The earlier descriptions of the possible functions of the Mauthner
neuron were not derived from physiological experiments but were based
on (1) the anatomy of the neuron, the origins of certain inputs to it
and the apparent destinations of many of its outputs; and ( 2 ) the
observations that most fish have well-developed startle-responses, rapid
escape-swimming reactions, and good equilibration function, Some
of these descriptions may turn out to be correct, but it is well to remember that elasmobranchs, for example, are not lacking in the reflexes
J. DZAMOND
IX. The Functions of the Mauthner Cells
.
. . . . . 331
A. Swimming and Equilibration: Two Improbable Functions . 331
B. Directionality Sensing: An Error
. . . . . . 338
C. The Avoidance Reaction: A Genuine Function
. . . 338
D. The Functions of the Collateral Inhibition
. . . . 340
E. Functions in Different Species: Unanswered Questions . 343
References
. . . . . . . . . . . . . 344
I. INTRODUCTION
The discovery of the giant axons bearing his name dates from Mauthner’s study in 1859. However, the association of these paired axons in
the spinal cord of teleost fish and certain amphibians with two remarkable cells in the brain (cells which were first described by Mayser in
1881) was only established later (Goronowitsch, 1888). These two cells
are fairly clearly related to certain brain nuclei, and especially to the
VIIIth cranial nerves; their possible function is usually discussed primarily
in that context. The earliest and certainly one of the most detailed and
interesting examplcs of such discussion can be found in the paper by
Bartelmez ( 1915). Moreover, because of their distinctive shape and
synaptic morphology as seen by light microscopy, the name Mauthner
cell has become associated largely with the soma-dendritic complex
in the medulla oblongata. The traditional approach, therefore, has tended
to relcgate the massivc spinal component of the Mauthner neuron to the
“nonintegrative” role of simply relaying information from the brain to
spinal motoneurons, which then drive the body muscles. This simplified
view is misleading. We shall see how the characteristics of the particular
spinal circuitry of which the Mauthner neurons are a part might well
define the limits of probable functions of these cells. The richness of
the neural inputs to, and intcrconnections between, the two Mauthner
neurons in the brain is remarkable and intriguing; it has, however, to be
interpreted with close regard to the findings in the spinal cord. Only
then can a satisfactory estimation of the total functions of what we
may call the Mauthner cell system be made.
The earlier descriptions of the possible functions of the Mauthner
neuron were not derived from physiological experiments but were based
on (1) the anatomy of the neuron, the origins of certain inputs to it
and the apparent destinations of many of its outputs; and ( 2 ) the
observations that most fish have well-developed startle-responses, rapid
escape-swimming reactions, and good equilibration function, Some
of these descriptions may turn out to be correct, but it is well to remember that elasmobranchs, for example, are not lacking in the reflexes