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General Morphology of Nematodes
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NERVOUS SYSTEM
The nervous
system in nematodes comprises essentially of three parts namely : (1)
the central nervous system, (2) the peripheral nervous system, and (3)
the peripheral nerve net.
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The Central nervous
system:
The most recognizable part is the nerve
ring which encircles the isthmus region of the oesophagus. The nerve
ring is associated with a number of ganglionic masses, with the
ventral ganglion as the most conspicuous. There are six nerve trunks
extending anteriorly from the nerve ring and innervating the sensory
organs, tracto-receptors (sensory papillae) or setae and/or
chemoreceptors (amphids), at the anterior extremity. The nerves
running posteriorly are connected with each other by means of
commisures.
The
paired post-anal lateral sensory organs (phasmids), the ventral
supplementary organs of males and the caudal papillae are all
innervated by branches from one or the other of the main nerves. The
nerves themselves and their branches can not be seen without special
methods for demonstrating them or by means of sectioning.
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Peripheral nervous system:
These innervate deirids and
hemizonid in addition to amphids and genital papilla. In routine
microscopic examinations, the only part of the nervous system visible is
the nerve ring which surrounds the isthmus region of the oesophagus.
Even this is often difficult to observe.
Peripheral nerve net:
In Adenophorea, in addition to the
central and peripheral nervous systems, a peripheral nerve net also
exists which links somatic and papillae, which, in turn, are connected
to the sensory neurons of the peripheral nervous system.
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