The nervous system of Earthworms is a complex network of cells and tissues that plays a crucial role in coordinating and regulating the activities of the body. It consists of three main components:
- Central nervous system (CNS)
- Peripheral nervous system (PNS)
- Sympathetic nervous system
Central Nervous System (CNS)
The CNS is composed of a brain ring or circumpharyngeal ring and a ganglionated double ventral nerve cord.
The circumpharyngeal ring is located in the 3rd and 4th segments. It is present around the dorsal surface of the pharynx.
It contains two supra-pharyngeal ganglia, two circumpharyngeal connectives, and a pair of sub-pharyngeal ganglia.
Ventral nerve cord
The ventral nerve cord arises from the subpharyngeal ganglia and is double and solid, with paired ganglia present in each segment.
Subpharyngeal ganglia form a ventral nerve cord. It extends up to the last segment on the ventral side of the alimentary canal.
Peripheral nervous system (PNS)
The PNS consists of nerves that extend from the CNS to supply various parts of the body. These nerves are of mixed nature, meaning they contain both sensory (afferent) and motor (efferent) nerve fibers.
Two pairs of nerves arise from the brain and innervate the prostomium and buccal cavity.
Nerves from the circumpharyngeal connectives supply the first and second segments, while the sub-pharyngeal ganglia send nerves to the second, third, and fourth segments.
Each segmental ganglion (which is actually paired) gives rise to three pairs of segmental peripheral nerves, with one pair from the anterior part and two pairs from the posterior part. These segmental nerves supply various structures within each segment.
Sympathetic nervous system (PNS)
The sympathetic nervous system is another component of the nervous system and consists of various nerve plexuses present in the wall of the alimentary canal. These plexuses help regulate the functions of the digestive system.
Note – Neurons in earthworms are motor, sensory, and adjuster type.
Sense organs are specialized groups of cells found in the skin and lining of the buccal cavity that allow organisms to perceive and interact with their environment. There are different types of sense organs present:
These receptors are located in the prostomium (the first segment of the body) and dorsal epidermis. They perceive light intensity with the help of a phaosome, which is an optic organelle.
The ability to see is not present in earthworms, which use photoreceptors to determine the intensity and duration of light.
- Thigmoreceptors / Epidermal receptor
These receptors are found in the ventral and lateral epidermis and are responsible for perceiving touch or pressure sensations.
These receptors are located in the lining of the buccal cavity and are involved in perceiving odors or smells.
- Gustatory receptors / Buccal receptors
These receptors are also found in the lining of the buccal cavity and are responsible for perceiving taste sensations.
In conclusion, the nervous system of Earthworms is a complex network that consists of the CNS, PNS, and sympathetic nervous system. The CNS includes the brain ring and ganglionated double ventral nerve cord, while the PNS comprises nerves that extend from the CNS to supply various body parts.
The sympathetic nervous system is involved in regulating digestive functions. Sense organs are specialized cells found in the skin and buccal cavity, including photoreceptors, thigmoreceptors, olfactoreceptors, and gustatory receptors, which allow organisms to perceive and interact with their surroundings.
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