Nervous_System_of_Earthworm which is connected with different nerves

Helps to know about earth worm

1. Nervous System of Earthworm

2. Nervous System of Earthworm Well developed and concentrated  nervous system. Group of organs and tissues associated with conduction of impulses. It is present on the ventral surface. Consists of 3 parts: A . Central nervous system (CNS) B . Peripheral nervous system (PNS) C . S ympathetic   nervous system (SNS)

3. Fig: Nervous system of Earthworm

4. A . Central nervous system It comprises of the anterior  nerve ring  or  brain ring  and the posterior  ventral nerve cord . Nerve ring Comprises of  cerebral ganglia or supra-pharyngeal ganglia ,  circumpharyngeal connectives,  and  subpharyngeal ganglia . Lies between 3 rd and 4 th segment . i . Suprapharyngeal ganglia: Also called cerebral ganglia or brain. It is bilobed , fused mass of ganglia.

5. Lies in 3 rd segment on the dorsal surface. ii. Circumpharyngeal connectives: There is a pair of circumpharayngeal connectives arises from both sides if cerebral ganglia. It encircles pharynx. It joins below pharynx in 4 th segment. iii. Subpharyngeal ganglia: It is fused part of two circumpharyngeal connectives. It is present in 4 th segment.

6. 2. Ventral nerve cord It is white rod like structure. It starts from 5 th segment to last segment. It appears to be single but really is double and made of 2 longitudinal cords fused together. Histologically , the nerve cord consists of  nerve fibers  and  nerve cells . It is covered by a common sheath containing: Outer ( Peritoneurium ), Middle (Longitudinal muscle fibres ) and Inner (epineurium of connective tissue)

7. N erve cords are separated internally by a vertical epineurium . The nerve cords swells in each segment. And the swelling structure is called segmental ganglion . In the region of segmental ganglia , 2 cores of nerve fibers are completely fused along the middle line .

8. B . Peripheral nervous system It includes nerve fibres or nerves which arise from central nervous system. Nerves arising from cerebral ganglia: Cerebral ganglia produces 8-10 nerves. These nerves supply information to prostomium , buccal chamber, pharynx. ii. Nerve arising from circum -pharyngeal connective: It produces 2 pairs of nerves. It supplies information to 1 st and 2 nd segments

9. iii. Nerves arising from sub pharyngeal ganglia: It produces three pairs of nerves. It supplies information to 2 nd , 3 rd , and 4 th segments. iv. Nerves arising from segmental ganglia: It also produces three pairs of nerves. It supplies information to respective adjacent segments. They include afferent and efferent nerves.

10. 3. Sympathetic nervous system It consists of   nerve plexus  situated in the wall of the alimentary canal. It is extensively branched or network. Such plexuses are connected with the circum pharyngeal connectives by fine nerves. They help in coordinating the functions of the related organs: On the inner surface of body wall. On the surface of body alimentary canal. To visceral organ.

11. Functions of the Nervous System in Earthworms : Coordination of Movements: nervous system helps to coordinate muscular movement, allowing the earthworm to move through the soil . Response to Stimuli: earthworm responds to light, touch, and chemicals in its environment (reflex actions ). Behavioral Actions: nervous system controls the earthworm’s behavior, such as moving toward or away from stimuli.

12. Hypothetical Scenario:Earthworm Exposed to Bright Light When an earthworm is exposed to bright light, its nervous system plays a crucial role in detecting the stimulus (the light) and generating an appropriate response. Let’s break this down step by step using the Stimulus → Sensory Input → Brain Processing → Motor Output → Action model . Stimulus : Bright light . Sensory Input: Light-sensitive receptors in the earthworm's skin detect the light and send signals via sensory neurons . Brain Processing: The cerebral ganglion interprets the signal and processes the light as a threat . Motor Output: Segmental ganglia send motor signals to the muscles, instructing them to move . Action : The earthworm moves away from the light by either burrowing deeper into the soil or retreating in the opposite direction.