Nervous system in non chordate

1. Nervous system in Non chordate
Dr. Sonia Bajaj
Assistant Professor
Department of Zoology
Shri Shankaracharya Mahavidyalaya ,Junwani ,Bhilai

2. Nervous system
• The nervous system (NS) of invertebrates and vertebrates is composed of two main types of cells: neurons
and glia.
• The most common form of neuron in the central nervous system. Unipolar neurons. Usually only found in
invertebrate species, these neurons have a single axon.
• Nervous System in Protozoa
• Protozoans lack specialized nervous system to respond to the environment.
• Single cell function as both the receptor and the effector.
• Contain an eyespot that act as a light sensitive receptor.
• Nervous System in Porifera
• Poriferans or the sponges are the only multicellular animals without a nervous system.
• They do not show any neurons or sensory cells.
• Although they lack a nervous system they are sensitive to pressure and touch that helps in their locomotion.

3. Phylum Cnidaria is also known as Phylum Coelenterate.
• Nervous System in Coelenterate.
• Cnidaria - The brain and central nervous system are absent in them.
• Nervous system is diffused type.
• Sensory neurons, intermediate neurons and motor neurons
• are present.
• These neurons are connected together by synapses.
• Synapses carry impulses to both directions within the nerve net.
Hydra sp. Nerve net is present. Contain multipolar neurons.
• Hydra, a cnidarian shows the diffuse nervous system, which is the most
primitive nervous system.
• The cnidarians are thus the first animal group showing true simple nervous
system. It consists of the sensory cells and the nerve cells or neurons along
with their fibres.
• The nerve cells are scattered or distributed throughout the body and inter
connected to each other by synapses between their fibres to form the nerve
net. There are two nerve nets both in the mesoglea, one connected towards he
epidermis and second towards the gastrolermis.

4. Nervous system in Platyhelminthes
• Planaria is a flatworm belonging to the phylum Platyhelminthes.
• It is the most primitive animal with a central nervous system (CNS) located on the
ventral side of body.
• There are also two eye spots that are connected to the brain and have receptor cells
sensitive to light, pressure, touch, and chemical stimuli.
• The sensory cells write together and form special rounded bodies, called cerebral
ganglia.
• It consists of a mass of cerebral or cephalic ganglion appearing like an inverted U shaped
brain.
• These lie in the anterior or head region and from each ganglion arise nine branches
towards the outer side.
• From each cerebral ganglion a long nerve cord arises and runs up to the posterior end
of the body.
• The two nerve cords are connected to each other by small nerves, in this way a ladder
type structure is formed.

5. Nervous system in Aschelminthes or Nemathelminthes
• It consists of a rich ganglionated nerve ring or circumenteric ring around the
pharynx.
• The nervous system of Ascaris consists of circumpharyngeal ring that carries a
dorsal ganglion, a subdorsal ganglion, lateral ganglia and ventral ganglion that
forms nerves forward and backward in the body.
• From the circumpharyngeal ring six small nerves supply the sense organs of the
anterior side. Posteriorly six longitudinal nerves arise from the ring and reach
the posterior end. They are mid dorsal nerve, mid ventral nerve, one pair of
dorsolateral nerves and one pair of ventrolateral nerves.
• . The ventral nerve forms a ganglion just in front of the anus.
• Dorsal, ventral and lateral nerve cords are interconnected.
• Sensory organs are present and they are of three types namely Papillae,
Amphids, Phasmids.
• Papillae are present on the lips, surrounding the mouth.
• Phasmids are chemoreceptors opening on either side of the tail.
• Amphids are two, situated on each, on each latero-ventral lip. These are
chemo-receptors.

6. Nervous system in Annelida
Nervous system is well developed and metameric in earthworm. It consists of
three parts- central, pheripheral and sympathetic nervous system.
(1) Central nervous system-It consists of an anterior nerve ring and a ventral
nerve cord.
• Nerve ring is formed by paired cerebral ganglia, peripharyngeal connectives
and sub-pharyngeal ganglia.
• A pair of cerebral or suprapharyngeal ganglia are found on the mid-dorsal
region of buccal chamber and pharynx which are also called brain.
• Nerve cord arises from the sub-pharyngeal ganglia which runs backwards in
mid-ventral line up to the posterior end of the body.
(2) Peripheral nervous system From each cerebral ganglia 8-10 nerves are given
out the buccal chamber.
• Nerves arising from the peripharyngeal connectives are supplied to
peristomium. Nerves from sub- pharyngeal ganglia supply structures in the
2nd, 3rd and 4th segments.
(3) Sympathetic nervous system-It consists of nerve plexuses spreaded in body
wall and the alimentary canal.
• These plexuses are connected with the peripharyngeal connectives and
regulate activities of internal organs.

7. Nervous system in Arthropoda
The nervous system of Palaemon consists of following 3 parts:(1) Central nervous
system,(2) Peripheral nervous system, (3) Sympathetic nervous system.
(1) Central Nervous System-It includes brain, a pair of circum-oesophageal
commissures and ventral nerve
(i) Brain-It is also known as supra-oesophageal ganglia. Brain is a bilobed structure
formed by the fusion of several ganglia. It is situated at the base of rostrum. 5 main
nerves are given out from each lobe of bilobed brain, antennular nerve ,ophthalmic
nerve, optic nerve, ophthalmic nerve, antennary nerve, tegumentary nerve.
(ii) Circum oesophageal commissures- A Circum oesophageal commissures aries from
each lobe of the brain which run backwards and downwards encircle the
oesophagus from their side and unite ventrally with the sub-oesophageal ganglia.
Both commissures are connected together by a transverse commissure near their
posterior ends.
(iii) Ventral nerve cord- Ventral nerve cord is found along the mid-ventral line of
abdomen just above the sternal plates. It is made of 17 pairs of ganglia out of
which first 11 pairs of ganglia belong to cephalothorax which fuse together to form
a large oval mass called ventral thoracic ganglionic mass. The ventral thoracic
ganglionic mass out of which first three pairs of nerves supply mandibles,
maxillulae and maxillae and remaining eight pairs of nerves supply eight pairs of
thoracic appendages. Each nerve going to walking legs become bifurcated before
entering the leg. An abdominal ganglion is found on ventral nerve cord in each
abdominal segment.
(2) Peripheral Nervous System-It consists of paired nerves arising from the brain and
ventral nerve cord.
(3) Sympathetic Nervous System-It consists of few ganglia and nerves.

8. Nervous system in Mollusca
Pila has well developed/ advanced nervous system. There are two specific features of
nervous system
(1) Except the visceral ganglia, all other ganglia form a ring-like structure around the
buccal mass.
(2) The visceral loop is '8'-shaped as a result of torsion. The nervous system of Pila
consists of ganglia, commissures and connectives.
1.The ganglia : there are paired ganglia which are the mass of nerve cells as well. The
following type of ganglia are present in Pila:
• Cerebral ganglia : It is present on dorso-lateral side of buccal cavity. Two (right & left)
cerebral ganglia are present, which are triangular in shape.
• Ganglionic mass : this is composed of pedal ganglion, pleural ganglion and other
nerves. There are to pleural-pedal (right & left) are Present in Pila.
• Buccal ganglia : It is present dorso-laterally near the joint of esophagus and buccal
mass.
• Supra instinal ganglion : this is present near pleura-pedal gangionic mass.
• Viceral ganglia : present at the end of visceral mass; two fused ganglia are there.
2.Commissures : the commissures always connects similar ganglia. There are three
commissures are present in pila. Cerebral Commissure, Pedal commissure, Buccal
commissure.
3.Connectives : the connectives always connect two different ganglia. Eight connectives
are present in pila.
• Two cerebral-buccal connective ,Two cerebral-pedal connective ,Two cerebral-pleural
connective ,Pleuro-infra intestinal connective, Supra-intestinal visceral connective,
Infra-intestinal visceral connective, Supra-intestinal pleural connective.

9. Nervous system in Echinodermata
• It is primitive and diffused type.
• It consists of nerve net consisting of nerve fibres and some ganglion cells. They
are present in the whole body.
• Neurosensory cells are present on the epidermis.
• They are of two types – tactile and olfactory.
• Tactile cells are found in the tube feet and olfactory cells are present around the
mouth.
• Sea star possess red eyespots at the end of each arm at the base of the terminal
tentacle.
The nervous system consists of -
1. Oral or ectoneural system -This system includes the main part of the nervous
system and is situated below the epidermis. This includes a nerve pentagon situated
in the peristomial membrane surrounding the mouth. The nerve pentagon at each
radius gives off a radial nerve which runs as a slender thick band throughout the
ambulacral groove of the arms. The radial nerve is situated just below the radial canal
as median integumentary thickening. The radial nerve ends as a sensory pad or
cushion at the base of the terminal tentacles.
2. Deep or hyponeural system--This nervous system comprises of Lange’s nerves,
which is a plate of nervous tissue situated beneath the coelomic epithelium of the
hypo-neural sinus and forms a lateral lining on the wall of this sinus.
3. Coelomic or Aboral nervous system-The sub-epithelial nerve plexus at the outer
ends of the ambulacral ossicles form marginal nerve cord on two sides of the arms. It
innervates the muscle of the body wall and gonads.

10. References
• A textbook of chordate-H.S. Bhamrah & kavita Juneja
• Invertebrate Zoology-P.S. Dhami & J.k. Dhami
• Modern text book of Invertebrate-R Kotpal
• Invertebrate Zoology 14 edition-Jordan & Verma