The neuronal basis of behavior in <i>Tritonia</i>. I. Functional organization of the central nervous system

Abstract

Abstract An account is presented of the brain (paired cerebral, pleural, and pedal ganglia) of the nudibranch mollusc Tritonia diomedia . The major efferent nerve fibers are related to their nerve cell bodies and their functional roles identified as far as possible. The channels of sesory input relating to some of these neurons are given so as to provide an overall view of the organization of the brain. A standardized system of abbreviation and notation for the central ganglia, nerve trunks, and gaint somata is proposed. The system of references is intended to provide a guide to the location in the ganglia of many of the smaller neurons of which the functional attributes are known, but which cannot be consistently recognized on visual criteria alone. A system of rectangular coordinates is proposed which is applied to the natural outline of the ganglia. In addition, a system of cell notation is described which is independent of the co‐ordinates used to define the position of the cell on the grid. Cell which by reason of their size, pigmentation, characteristic location and physiological attributes are consistently recognizable from animal to animal are numbered. Two principles were followed in numbering cells; (i) the series begins at unity in each ganglion; (ii) cell homologues in opposite ganglia are given the same number, but distinguished by prefixing the abbreviation for the ganglion in which they occur. It is considered that the system will facilitate the exchange of information between workers on the same species, and also benefit the comparison of neural organization of behavior in closely related forms. The brain is organized in an almost exactly bilaterally symmetrical manner. There are a few bilateral neural pathways, but the major functional routes are ipsilateral. A few motorneurons, which are uniquely identifiable anatomically, cause unique, discrete movements. Others are in small groups sharing overlapping or similar functions.