09 Control and Coordination - part 02 - Nervous System in Planaria (flatworm)

 

09 Control and Coordination - part 02 - Nervous System in Planaria (flatworm)


Nervous System in Planaria (flatworm) :

  • Planaria is a flatworm belonging to the phylum platyhelminthes. 
  • Most primitive animal with a central nervous system (CNS) located on the ventral side of body. 
  • It consists of a mass of cerebral or cephalic ganglion appearing like an inverted U shaped brain.
  • Lie in the anterior or head region and from each ganglion arise nine branches towards the outer side. 
  • Ventrally from below the ganglia arise a pair of Ventral Nerve Cords (VNC) or long nerve cords. 
  • These are inter connected to each other by transfer nerve or commissure in a ladder like manner. 
  • The peripheral nerve plexus arising laterally from VNC. 
  • The PNSinclude sensory cells arranged in lateral cords in the body. 
  • A pair of photosensory structure, the eyes are located on dorsal side of the brain.
  • Also there are single sensory cells scattered in the body.
  • In the above examples of Hydra, Planaria and the earlier studied examples of cockroach and humans, we have seen the gradual evolution or changes of the neural system.
  • There is a high level of specialization in the formation of neurons as electrically signalling cells and also in the entire system, gradually from a diffuse neural system to a centralized nervous system. 
  • The expansion into a properly organized system involving the brain, its gradual expansion in size and functions.
  • This has lead to centralization of various sense organs assisting in coordinating the internal environment with that of the external environment. 
  • Also there evolution of a complex networking system which efficiently transmits signals between one part or organ of the body and another.

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