the earliest evolution of the nervous system (a nerve net) occurred in animals like cnidaria.
the earliest evolution of the nervous system (a nerve net) occurred in?
animals like cnidaria
the evolution of nervous systems dates back to the first development of nervous systems in animals (or metazoans). neurons developed as specialized electrical signaling cells in multicellular animals, adapting the mechanism of action potentials present in motile single-celled and colonial eukaryotes. simple nerve nets seen in animals like cnidaria (jellyfish) evolved first, consisted of polymodal neurons which serve a dual purpose in motor and sensory functions. cnidarians can be compared to ctenophores (comb jellyfish), which although are both jellyfish, have very different nervous systems. unlike cnidarians, ctenophores have neurons that use electrochemical signaling. this was perplexing because the phylum ctenophora was considered to be more ancient than that of porifera (sponges), which have no nervous system at all. this led to the rise of two theories which described how the early nervous system came about. one theory stated that the nervous system came about in an ancestor basal to all of these phylum, however was lost in porifera. the other theory states that the nervous system arose independently twice, one basal to cnidarians and one basal to ctenophores. bilateral animals – ventral nerve cords in invertebrates and dorsal nerve cords supported by a notochord in chordates-- evolved with a central nervous system that was around a central region, a process known as cephalization.
evolution of nervous systems
the nerve net is the simplest form of a nervous system found in multicellular organisms. unlike central nervous systems, where neurons are typically grouped together, neurons found in nerve nets are found spread apart. this nervous system allows cnidarians to respond to physical contact. they can detect food and other chemicals in a rudimentary way. while the nerve net allows the organism to respond to its environment, it does not serve as a means by which the organism can detect the source of the stimulus. for this reason, simple animals with nerve nets, such as hydra, will typically produce the same motor output in response to contact with a stimulus regardless of the point of contact.
nerve net