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.