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Earthworm Nervous System Short Notes

In this article we will discuss about the earthworm nervous system

Earthworm Nervous System

Earthworm has a simple nervous system
Earthworm nervous system is consists of 3 parts: the central, peripheral, and Autonomic nervous system
Functions of earthworm nervous system is esponse to stimuli and help for movement

1. Central nervous system

The central nervous system consists of nerve ring and nerve cord

Nerve ring

It is ring like structure which lies around the pharynx in 3-4th segment
It has 3 parts:-

i) Supra-pharyngeal ganglia

They are bilobed in structure
Present on the dorsal side (3rd segment) of alimentary canal
Supra pharyngeal ganglia fused to form brain

ii) Circum-pharyngeal connectives

From either side of supra-pharyngeal ganglia, a pair of thick short band circum-pharyngeal connectives arise which enclose the pharynx
Circum-pharyngeal connectives meeting ventrally in 4th segment by a pair of fused sub-pharyngeal ganglia

iii) Sub-pharyngeal ganglia

Found in lower region of nerve ring which lies in 4th segment
From this, a ventral nerve cord runs towards the posterior region

Ventral nerve cord

It is long thread like double layered structure
Arises from the posterior part of sub-pharyngeal ganglia and runs the posteriorly up to the last segment of the body
Extends from 5th to last segment.
Nerve cord are two in number but they are fused. So they are called double ventral nerve cord.
It has swelling bulb like structure in each segment called segmental ganglion

2. Peripheral nervous system

Those nerve which arise from different parts of central nervous system are called peripheral nervous system.
From cerebral ganglia, 8-10 nerves arise and supply to prostomium, buccal chamber, and pharynx.
From subpharyngeal ganglia, three pairs of nerve arise and supply to 2nd, 3rd and 4th segment
From each segmental ganglion, three pairs of nerves arise and supply to respective segment.

3. Autonomic nervous system

The autonomic nervous system controls all the involuntary activities of the body
The nerve arises from circum pharyngeal and they form a network-like structure like plexus in the body wall and gut wall.

Sense organs of earthworm

Earthworms have well-developed sense organs.
Sense organs are simple in structure consisting of one single cell or a group of specialized ectodermal cells.

Epidermal receptors

These receptors are well distributed all over the epidermis
They are tactile in function and also respond to chemical stimuli and changes in the temperature

Buccal receptors

Receptors are restricted only to the epithelium of the buccal chamber.
These receptors are gustatory and olfactory in function They also respond to chemical stimuli

Photo receptors

These are photo sensitive or light sensitive receptors which are restricted only to the dorsal surface of the body.
They are totally absent in the clitellar region.
Photoreceptors enable worms to judge the intensity and duration of light.

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