Primitive nervous system - nerve net, Biology

Assignment Help:

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.


Related Discussions:- Primitive nervous system - nerve net

Explain the bunsen burner, Explain the Bunsen Burner? It is a type of g...

Explain the Bunsen Burner? It is a type of gas burner that gives very hot flame by allowing air to enter at the base and mix with the gas. It is used - (a) For sterilizing i

Tropical savannas, Leaving the deserts as you approach the tropical regions...

Leaving the deserts as you approach the tropical regions of the earth you will enter the savanna biome, which is a combination of grassland with scattered or clumped trees. These s

Explain heterozygous individual and homozygous individual, What is the ge...

What is the genetic condition in which the heterozygous individual has different phenotype from the homozygous individual? This situation is called lack of dominance and it can

What resources are competed for by animals, What resources are competed for...

What resources are competed for by (a) animals, (b) plants?  (a) Animals compete for food, mates and shelter.  (b) Plants compete for light, water and minerals.

Morphological changes - floral induction, Morphological Changes - Floral In...

Morphological Changes - Floral Induction Some of the morphological changes that accompany floral induction are: Change in the shape of meristem, Increase in the ra

Limb regeneration in anuran amphibians, Limb Regeneration in Anuran Amphibi...

Limb Regeneration in Anuran Amphibians We are already aware that the limb of adult frogs does not regenerate later than amputation. Though, some regeneration has been found to

Main prophylactic measures against hookworm disease, Q. What are the main p...

Q. What are the main prophylactic measures against hookworm disease? The major prophylactic measures against hookworm disease are to avoid walking barefoot on soils suspected o

Explain about metabolic diseases, Q. Explain about Metabolic diseases? ...

Q. Explain about Metabolic diseases? Metabolic diseases, as you already know, refer to those disorders in which the various reactions in the cells are effected (production of e

Death and its significance, DE A T H - It is universal. It is ...

DE A T H - It is universal. It is last event in the degenerative process of ageing. It involves widspread cell break down & cell death. There is no heart beat, n

Counselling process of diabetic patient, Let us first learn about learn the...

Let us first learn about learn the points counsellor has to keep in mind for positive outcome of the counselling. The counsellor achieves the positive outcome of counselling, couns

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd