Primitive nervous system - nerve net, Biology

Primitive Nervous System - Nerve Net

A nervous system creates its appearance for the first time in the phylogeny among Cnidaria. In this group the nerve cells make an irregular nerve net or plexus. In hydras we have a simple condition. The nerve net is build up of bipolar or tri-polar and rarely multi-polar neurons. The sensory nerve cells are distributed in between the epithelial cells; they send their nerve fibers to the sub-epithelial nerve plexus. The plexus is located beneath the epidermis. In hydroid polyps the plexus is concentrated around the mouth, suggesting the beginning of a centralised nervous system. Several cnidarians have more complicated nerve nets; for example they may have as well as gastro dermal nerve net within the gastrodermis in addition to the epidermal nerve net like in sea anemones. A double nerve net in the same body layer is also common in some coelenterates. There is quite a lot of autonomy, in that, isolated parts of the animal behave as if parts of the body. There is no central controlling mechanism apparently because there is no distinct central nervous system. It is as well poor in specific responses to particular stimuli. Transmission is un-polarised, in that impulse can be transmitted in either direction along the synapse not like in higher animals. This occurs because both terminals secrete transmitter substance. So the nerve plexus in this group shows diffuse, un-polarized transmission, autonomy of parts and scarcity of reflexes.

Posted Date: 2/4/2013 6:35:24 AM | Location : United States

Related Discussions:- Primitive nervous system - nerve net, Assignment Help, Ask Question on Primitive nervous system - nerve net, Get Answer, Expert's Help, Primitive nervous system - nerve net Discussions

Write discussion on Primitive nervous system - nerve net
Your posts are moderated
Related Questions
What is Class Gastropoda in animal kingdom? Snails and slugs are referred to as gastropods because of their characteristic body plan. "Gastro" is derived from the Greek word fo

BLASTUL A TIO N - Type of blastula is blastocyst or trophoblastula. Outer layer of cell becomes flat and form trophoblast or trophoectoderm which receives nutritive ma

The feasible methods of stabilization within the constraints of retaining natural status: Complex formation: Anthocyanin occurs naturally as complexes which are relatively st

Explain Principle of Fehling's Soxhlet method (Lane-Eynon method)? Reducing sugars are those which have free sugar groups and hence may be estimated directly by titrating the s

Explain Systematic - Modern Trends in Animal Taxonomy Systematic is defined as the study of relationship among organisms which means reconstruction of phylogenies. It is that b

Types of Cambium On the basis of the arrangement of the Fusiform cells as seen in tangential section, cambium is divided into: A) Storied/Stratified Cambium : The groups o

Q. What and how many are the pulmonary veins? The pulmonary veins are part of the pulmonary circulation they are vessels that carry oxygen-rich (arterial) blood from the lungs

ROLE OF PSYCHIATRIC NURSE: In Blocks 2 and 3 you have learnt about various therapeutic interventions  for mental disorders  like anxiety neurotic disorders, psychotic disorder

Guanotelism - Excretion Normal 0 false false false EN-IN X-NONE X-NONE MicrosoftInternetExplorer4

Q. Show Appearance of food product? Appearance can be judged by the eye. Appearance factors include such things as size, colour, uniformity, absence of any defect, shape, whole