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Segmental homology and variation in flexor motoneurons of the crayfish abdomen
Author(s) -
Mittenthal Jay E.,
Wine Jeffrey J.
Publication year - 1978
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.901770209
Subject(s) - soma , crayfish , biology , ganglion , anatomy , procambarus clarkii , neuroscience , peripheral , motor neuron , spinal cord , medicine , fishery
In the crayfish abdomen the anterior five of six ganglia are serially homologous. The locations and sizes of motoneuron somata of the fast and slow flexor systems have been determined by axonal infusion of cobalt. The somata form three clusters, distinguished by soma position in the ganglia and course of axons in the nerve cord. For the fast flexors, the anterior group shows the greatest departure from serial homology; it has one soma in the first ganglion (G1), three in G2 and G3, two in G4, and none in G5. The medial group contains the giant motoneuron, the peripheral inhibitor, and two smaller neurons in all five ganglia. The posterior group contains four somata in G1‐G4 and three in G5. The slow flexor motoneuron somata cluster into the same three groups. Intersegmental variations in soma size and in volume of muscle innervated are positively correlated for the giant motoneuron and for the peripheral inhibitors of both fast and slow flexor muscles. Corresponding clusters of neuropilar branches of the fast flexor peripheral inhibitor can be recognized in each of the anterior five abdominal ganglia of Procambarus . Inhibitors in G1‐G5 occupy roughly corresponding positions with respect to the dorsal giant interneurons and receive similar inputs. Ganglia of the crayfish abdomen were compared by using the positions of serially homologous somata to define a mapping from each ganglion onto G2. The mappings support the conventional view that G2, G3, and G4 are typical abdominal ganglia, while G1 and G5 show special end effects. Groups of flexor motoneurons homologous to the three groups in crayfish, and to some extent homologous neurons, can be recognized in ganglia of other decapod crustacea. Groups of motoneurons that are strikingly similar to the groups in decapod crustacea appear in several orders of insects. The groups in crustacea and insects may be homologous, and corresponding groups may exist widely within the Articulata. These apparent intersegmental and interspecific homologies suggest homology of large‐scale features of ganglionic organization.