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A nerve net is a type of simple nervous system that is found in members of the cnidaria and echinodermata phyla . Nerve nets consist of interconnected neurons lacking a brain or any form of cephalization. This nervous system allows cnidarians to respond to physical contact. They may then detect food and other chemicals in a rudimentary way. Although the nerve net allows the animal to respond to its environment, it has trouble alerting the animal from where the stimulus is coming. For this reason, simple animals with nerve nets, such as hydra, will typically respond in the same way to contact with an object, regardless of where the contact occurs.

Hydra, which are cnidarians, have a nerve net throughout their body. On the other hand, Sea stars, which are echinoderms, have a nerve net in each arm, connected by a central radial nerve ring at the center. This is better suited to controlling more complex movements than a diffuse nerve net .

[edit] See also

• Ventral nerve cord in Arthropods
• Dorsal nerve cord in Chordates

[edit] References

• Kass-Simon G, Pierobon P. Cnidarian chemical neurotransmission, an updated overview. Comp Biochem Physiol A Mol Integr Physiol. 2007 Jan;146(1):9-25. Epub 2006 Sep 22. PMID 17101286
• Miljkovic-Licina M, Gauchat D, Galliot B. Neuronal evolution: analysis of regulatory genes in a first-evolved nervous system, the hydra nervous system. Biosystems. 2004 Aug-Oct;76(1-3):75-87. PMID 15351132
• Koizumi O, Mizumoto H, Sugiyama T, Bode HR. Nerve net formation in the primitive nervous system of Hydra--an overview. Neurosci Res Suppl. 1990;13:S165-70. PMID 2259484
• Shimizu H. Feeding and wounding responses in Hydra suggest functional and structural polarization of the tentacle nervous system. Comp Biochem Physiol A Mol Integr Physiol. 2002 Mar;131(3):669-74. PMID 11867292
• Sakaguchi M, Mizusina A, Kobayakawa Y. Structure, development, and maintenance of the nerve net of the body column in Hydra. J Comp Neurol. 1996 Sep 9;373(1):41-54. PMID 8876461
• Gillis MA, Anctil M. Monoamine release by neurons of a primitive nervous system: an amperometric study. J Neurochem. 2001 Mar;76(6):1774-84. PMID 11259495
• Grimmelikhuijzen CJ, Westfall JA. The nervous systems of cnidarians. EXS. 1995;72:7-24. PMID 7833621

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