Coordination: NERVOUS SYSTEM OF HYDRA

 

Q:   Describe the nervous system of Hydra?

 

ANS:-   NERVOUS SYSTEM OF HYDRA

 

         The coelenterates such as Hydra are the animals which exhibit the first well-defined nervous system. It consists simply of a network of impulse somewhat similar nerve cells ramifying through most of the organism. The nerve cells are inter-connected by means of synapses which are microscopic gaps between end of neurons. There is no central control in this animal there is no accumulation of neurons in the form of ganglia or ‘brain’. Nerve impulse conduction is slow and can occur in either direction. The response is almost localized. However some neurons may be differentiated either as receptors, transmitters as effectors.

 

 

Hydra showing the nerve net, a nerve cell in the ectoderm

 

Hydra has no specialized muscle cells but most of the inner and outer cell layers of the animal can contract. The response is greatest near to the point of stimulation and gets progressively less in the more distant regions. If Hydra is stimulated violently, it has the power of contracting very suddenly. But Hydra performs only limited movements. Tentacles are more contractile than the rest of the body but it can bend and shorten its body.

 

Q:  Describe nervous system of planarian?

 

Ans:-NERVOUS SYSTEM OF PLANARIAN

 

The nervous system of planarian is very different from that of Hydra.                   The nervous tissue is especially concentrated into a bilobed mass called cerebral ganglia or ‘brain’ in the anterior region of the body. From brain a pair of longitudinal tracts or nerves called nerve cords extend all along the entire length of the body. The nerve cells of these nerve cords serve as link between stimulus and response. The ganglia or brain act as a co-ordinating center for the various nerve impulses. The anterior region is also provided with sense organs in the form of eyes and chemo-receptors.

      

Nervous system of planaria

Flatworm show more varied behaviour and more rapid responses. If the cerebral ganglia are removed locomotion, feeding and breeding is upset but the action of the cilia of the body is not disturbed which seem to be controlled by the superficial nerve net. The receptor cells are sensitive to light, pressure, touch and chemical stimuli.