The Relationship Between Planarians And A Centralized Nervous System
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Planarians are members of the Platyhelminthes (flatworm) family and are triploblastic organisms whose tissues arose from the three germ layers namely; ecto-, meso- and endoderm. They act as a good model for cell proliferation and therefore regeneration. Planarians are composed of many organ systems including a centralized nervous system (CNS) which is made up of bi-lobed cephalic ganglia that are positioned at the anterior end of the body. These ganglia are linked to two longitudinal ventral nerve cords that run posteriorly along the worm. Planarians ingest and excrete through a muscular feeding tube connected to the gut. The gastrovascular system is also composed of three intestinal branches that deliver the nutrients.
Planarians can…show more content… In the last ten years, research on planarians has been greatly improved with two members of the phylum being worked with, S. mediterranea and Dugesia japonica. S. mediterranea were used because of their regenerative abilities and their small genome size in comparison to other planarian members. They also exist as two biotypes which allows for comparison between asexual and sexual reproduction.
As mentioned already planarians regenerate by epimorphosis and following amputation, planarians undergo depolarization. During regeneration, polarity of the body axis is controlled by the species. The polarity is categorized into three orientations namely; anterior-posterior (A/P), dorsal-ventral (D/V) and medial-lateral (M/L).
Over the years, research has been carried out on the interaction between polarity and regeneration. Following amputation, “germs” present in the planarian can be transported both anteriorly and posteriorly to allow the regrowth of the head and tail. Other research carried out by Brøndsted concluded that A/P polarity was brought about by unknown effectors through a time-graded regeneration field. In this field, points were revealed in the blastemal where regeneration took place faster in the head region than in other areas leading to the release of factors that prevented head formation in posterior regions. Morgan’s discovery is the most prominent with regard to