Introduction
The nervous system is the part of an
animal that coordinates its actions by
transmitting signals by nerve impulses, to
and from different parts of its body.
The nervous system performs three basic
functions; receives stimuli through sensory
neurons from internal and external environment
and passes to the brain; where the input stimuli
is processed and then response is given back
to the body parts through motor neurons.
Functional Unit of nervous system is neuron or
nerve cell. Nervous system is absent in plant
kingdom.
Nervous system in Animal kingdom
The nervous system evolved from a simple
sting cell, nerve ganglion, and neurons to
brain.
- Nervous system in protozoans:
The protozoans lack nervous system. - Nervous system in coelenterates:
The coelenterates are multicellular organisms.
The nerve net is the simplest form of a nervous
system found in multicellular organisms.
Unlike central nervous systems, where
neurons are typically grouped together,
neurons found in nerve nets are found spread
apart. Hydra, which are cnidarians, have a
nerve net throughout their body.
3. Nervous system in Platyhelminthes: They
have a nerve net. The nervous system of the
flatworm has an organisation different from
the invertebrates described above. It does
have a nerve net, but these are connected by
long nerve cords. These cords are connected to
cerebral ganglia located in the head region.