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
Define Gender Discrimination - Public Nutrition? Of the detrimental factors, that affect food security, gender discrimination is the most pervasive and vicious. The fact that h

Posterior Leaflet: In the posterior leaflet a quadrangular excision of the sector involved in the prolapse is done. This may be up to 15-20 per cent of the leaflet. The remaining

what is the opposite of yield? A.grow B.attack C.ask D.answer

Explain about Osteogenesis Osteogenesis, large amounts of woven bone can be formed very rapidly. This bone is believed to be much more compliant than organized lamellar bone. I

Define Disadvantages of using yeast as a source of protein? 1. Less protein yield (45-60%) 2. Growth rate is low (1-3 h) 3. High nucleic acid content leading to the forma

Healthy Person H takes a new drug named ANTICAMPCOLLDUCT that blocks the production of cyclic AMP (cAMP) in collecting duct epithelial cells in response to vasopressin binding to V

Q. What do you mean by Systematic Zoology ? It contains articles on animals systematic, and papers dealing with cytological attributes of species and higher taxa, distribution p

Explain Antigens ? A blood type, or group, is based upon the presence or absence of certain substances called antigens on the surface of the red blood cells. Antigens are subs

In arthropods why isn't gas exchange done through cutaneous diffusion? In arthropods the impermeability of the exoskeleton makes the passage of gases complex. In addition the n

Explain Saquinavir Saquinavir (SQV, Fortovase, Invirase) - When administered as a single protease inhibitor, a soft-gel preparation (Fortovase) with improved bioavailability an