Abstract
Many theories and arguments have been proposed regarding the ancestors of the vertebrates
and the factors that lead to the evolution of the tubular nervous system. Invertebrates
had simpler smooth muscles. Vertebrates acquired additional skeletal muscles. The
skeletal muscles were found to be associated with a new type of tubular nervous system.
There were three stages in the evolution of the nervous system. The most primitive
was the network type, in which there was neither a polarization nor a centralization
of neurons. The second stage was characterized by the evolution of a ganglionic nervous
system. Then, the tubular type of nervous system appeared for the first time in chordates.
Therefore, the author hypothesizes that the skeletal muscle developed simultaneously
with the tubular nervous system. The chorda mesoderm and, thereby, the skeletal muscle,
induced the formation of a tubular nervous system in chordates. In the present article,
the author aims to analyze the nervous system, starting from invertebrates and moving
on to chordates.
Keywords
nervous system - skeletal muscle - chordates - mesoderm
