Ventral nerve cord

A ladder nervous system (also metameric nervous system ) is a nervous system that consists of a plurality of segmental ganglia arranged pairs. The intrasegmental connected " rungs" are referred to as commissures, the intersegmental " bars " on the left and right connectives.

This lying ventrally usually nervous systems, which are therefore also referred to as the ventral nerve cord, are typical of several animal strains of Urmünder ( Protostomia ), especially for the

• Arthropods ( arthropods, such as insects, arachnids, crustaceans)
• Water bears ( tardigrades )
• Velvet worms ( Onychophora )
• Segmented worms ( Annelida )

Each segment of the body contains two ganglia or a grown together from the two Fusionsganglion which serves in particular to control the organs of this segment. In the head region also several ganglia are usually fused into a Oberschlundganglion ( cerebral ganglion ), which is referred to in arthropods and tardigrades as the brain perceives and higher-order functions.

Importance of the rope ladder nervous system for taxonomy

The evolutionary origin of the ladder nervous system is not yet fully understood. The nervous system of molluscs may perhaps - as the rudimentary trained ventral nerve cord of the chitons shows - be evolutionarily traced back to a rope ladder nervous system and would be in the common ancestral species of lophotrochozoans ( molluscs, annelids, etc. ) and the Ecdysozoa ( arthropods, nematodes, etc.) originated. Some members of these groups, it would be gone then been subsequently replaced by another form of the nervous system or lost. If it is however, in the nervous system of molluscs is a matter arisen nervous system, the rope ladder nervous system would underpin the summary of the classical taxon of the arthropods ( Articulata ) with the annelids, tardigrades, and arthropods Stummelfüßern. For this reason, it is considered one of the most important arguments for the representatives of the " Articulate " theory.

Swell

• V. Storch, U. Welsch, Kükenthal - Zoological internship, 24th edition, Spektrum Akademischer Verlag, Berlin, 2002.