Nervous system of Earthworm
The nervous system of earthworms comprises a ventral nerve cord, paired ganglia, and peripheral nerves, which work together to control movement, sensory perception, reflex actions, and survival behaviours. This is a vital NEET and Class 11 Biology topic in invertebrate physiology.
This Story also Contains
- What is the Nervous System of Earthworms?
- Overview of Nervous System
- Structure of Nervous System
- Sense Organs in Earthworm
- Functions of Earthworm Nervous System
- Role of Nervous System in Behavior
- Comparison with Other Invertebrates
- Evolutionary Significance of Earthworm Nervous System
- Nervous System of Earthworm NEET MCQs (With Answers & Explanations)
What is the Nervous System of Earthworms?
The nervous system of earthworms is a very intricate network used in the coordination of their movement and general reaction towards the environment. It involves the central nervous system and the peripheral nerves for the various sensory and motor functions. The nervous system would, therefore, take the lead in the earthworm's behaviour in feeding, reproduction, locomotion, and other activities.
Overview of Nervous System
Earthworms have a decentralized nervous system that is believed to have caused the performance of complex body movements and responses to stimuli. Decentralization makes the system well adapted to the way of life of an earthworm in that it serves the worm as an aid when it comes time for travelling through the soil and producing quick answers to threats.
Structure of Nervous System
The nervous system of the earthworm is made up of a ventral nerve cord, ganglia, and peripheral nerves.
Ventral Nerve Cord
A ventral nerve cord of the earthworm runs lengthwise through the body, attached to the ganglia facilitating communication across the earthworm.
It appears to be single but it is double, consisting of two compactly united right and left cords.
Ganglia
It has been stated that each segment of an earthworm contains a set of ganglia which works as the local controller controlling all the body movements.
Also, the sensory information is processed at these structures.
These structures perform the task of integrating information from the environment and coordinating the appropriate responses.
Sense Organs in Earthworm
Earthworms have well-developed sense organs which are quite simple in structure. It has three types of sense organs or receptors.
Epidermal Receptors
These are distributed all over the epidermis but are more abundant on the lateral sides and ventral surface of the body.
They are tactile (related to touch) in function and also respond to chemical stimuli and changes in temperature.
Buccal Receptors
These are confined to buccal chambers.
They are gustatory and olfactory and probably respond to chemical stimuli.
Photo-receptors
They are present on the dorsal surface and gradually reduce in number towards the posterior end of the body.
It enables worms to judge the intensity and duration of light.
Functions of Earthworm Nervous System
The function of nervous system of Earthworm are:
Sensory Mechanisms and Response
The nervous system in earthworms caters to response to changes in the environment, for example, light and moisture.
Immediately after the stimulated status is achieved, the nervous system of the earthworm triggers a line of responses that make it possible for the organism to adopt the stimulation in its environment and therefore survive.
Coordination of Movement
The coordinated contractions of the muscles are used in moving through burrows and about in soil by burrowing in; the earthworm is coordinated by the nervous system.
The earthworm needs to have this coordination for its survival since it will help it search for food, escape from predators, and mate successfully.
Reflex Actions
Earthworms do indeed demonstrate reflex actions to stimulations, therefore justifying a feature of rapid responses to danger.
The nervous system mediates and controls these reflex reactions and fairly well equips the earthworm to preserve its biological integrity from potential harm.
Role of Nervous System in Behavior
The nervous system plays an important in deciding the behaviour of the earthworm:
Most of the activities of the earthworm about feeding, mating, and locomotion are controlled by its nervous system.
It integrates all the diversified activities involving survival and reproduction for the sustenance of the species.
Comparison with Other Invertebrates
A nervous system in an earthworm is really simple if we compare it to that of higher animals. Yet, with their life habits, it functions just fine. It allows successful coordination of motions and perception, therefore letting them thrive in such an environment as soil.
Evolutionary Significance of Earthworm Nervous System
The study of earthworm nervous anatomy contributes a lot to the knowledge of how the nervous systems of higher animals evolved. In the attempt to understand how this system works in the lower animal, a lot of information is passed regarding the development and adaptations of animals in the animal kingdom.
Nervous System of Earthworm NEET MCQs (With Answers & Explanations)
Important topics for NEET are:
Structure of nervous system
Sense organs
Practice Questions for NEET
Q1. Ventral nerve cord of earthworm
Arises from anterior part of pharyngeal ganglia
Runs posteriorly up to last segment
Nerve cord are two in number and they are free
Arises from 8th segment
Correct answer: 2) Runs posteriorly up to last segment
Explanation:
As we learned Ventral Nerve Cord Arises from the posterior part of the sub-pharyngeal ganglia (from the 5th segment) and runs posteriorly up to the last segment. Nerve cords are two in number, but they are fused so-called double.
Hence, the correct answer is option 2) Runs posteriorly up to the last segment
Q2. Which of the following structure is not a part of nerve ring in earthworm?
Subpharyngeal ganglion
Suprapharyngeal ganglion
Circumpharyngeal connectives
Segmental ganglion
Correct answer: 4) Segmental ganglion
Explanation:
Neural System of Earthworm – The nervous system of an earthworm consists of a ventral paired nerve cord, which enlarges in each segment to form segmental ganglia. In the anterior region (3rd and 4th segments), the nerve cord bifurcates, encircles the pharynx laterally, and connects to the cerebral ganglia dorsally, forming a nerve ring. This nerve ring, made up of the cerebral ganglia, subpharyngeal ganglion, and circumpharyngeal connectives, is a characteristic feature of the earthworm. The cerebral ganglia receive and process sensory inputs, converting them into appropriate body responses.
Hence the correct answer is option 4) Segmental ganglion.
Q3. In earthworm, sympathetic nervous system present in
Pharynx
Lymph gland
Alimentary canal
Gizzard
Correct answer: 3) Alimentary Canal
Explanation:
The nervous system
The ventral paired nerve, which grows in each segment to generate segmental ganglia, makes up the nervous system of earthworms.
To create a nerve ring, the nerve cord in the third and fourth segments (the anterior region) bifurcates, encircles the pharynx laterally, and attaches dorsally to the cerebral ganglia.
Together with cricopharyngeal connectives, the cerebral ganglia and subpharyngeal ganglion form the nerve ring.
One feature of earthworms is the existence of nerve rings.
The sensory outputs are received and processed by the brain ganglia and related nerves in the nerve ring, which then translates them into bodily reactions.
Hence, the correct answer is option 3) Alimentary canal.
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Frequently Asked Questions (FAQs)
The nervous system of the earthworm is decentralized and consists of an anterior simple brain that acts to refine sensory information, and a main ventral nerve cord that runs along the length of its body with segmental ganglia at each segment of the body, to process sensory information locally and also to control the movements at each segment.
The stimuli to which this earthworm shows sensitivity include a wide range from light and moisture to chemical signals. Specialized sensory organs on the surface of the body help in determining such stimuli so it acts in different manners according to various changes in its environment.
Earthworms respond to some changes in their environment through reflex actions intermingled with voluntary action. In the process of perceiving a change in their environment, their nervous system responds quickly to information derived from detected sensory input. Information processing is fast and hence facilitates fast responses to protecting the body or affecting a modification in their habitats if there is a threat or environmental change.
Ganglia in the body of an earthworm are the local processing centers of the nervous system. Each segment has a ganglion that receives sensory information from that segment and coordinates muscle contraction to produce movement. Such a decentralized nature allows efficiency and the possibility of having coordinated responses stimulated throughout the body.
The nervous system is mainly for locomotion and responses to environmental stimuli. It processes the sensory information and controls the contractions of muscles, enabling the earthworm to move through soils, locate food sources, avoid predators, and interact in mating activities.