Segmented nervous system in annelids.pptx

Segmented nervous system in annelids.pptx

1. segmented nervous system in annelids M.Yasheera Taj Reg.no : 22PZO25 Ist MSc.Zoology

2. Annelid The annelids also known as the ringed worms or segmented worms, are a large phylum, with over 22,000 extant species including  ragworms , earthworms, and leeches. The species exist in and have adapted to various ecologies – some in marine environments as distinct as tidal zones and hydrothermal vents, others in fresh water, and yet others in moist terrestrial environments. The Annelids are  bilaterally symmetrical,  triploblastic ,  coelomate , invertebrate organisms .

3. Earthworm - Annelid

4. Earthworm - Annelid Seventeen native species and 13 introduced species (from Europe) occur in the eastern United States. Earthworms occur in virtually all soils of the world in which the moisture and organic content are sufficient to sustain them. One of the most detailed studies of earthworm activities was conducted by English naturalist Charles Darwin.

5. Nervous system of Annelid The brain of most annelids (phylum Annelida ; segmented worms, including the leeches and terrestrial earthworms) is relatively simple in structure. The earthworm brain is a bilobed mass lying above the pharynx in the third body segment.

6. Nervous system of Annelid In some the brain of annelids can be divided into A forebrain A midbrain A hindbrain A single pair of circumesophageal or circumpharyngeal connectives leave the brain, surround the anterior gut, and connect with the ventral nerve cord.

7. Nervous system of Annelid In most annelids (segmented worms) such as the earthworm, two cerebral ganglia (bundles of nerve cells) form a primitive bilobed brain, from which sensory and motor nerve fibres lead to other areas of the body Sensory nerves leave the brain and run forward into the prostomium (extreme anterior end) and first segment. The brain of the active, predatory polychaetes (a class of marine worms) is more complicated.

8. Nervous system of Annelid The most primitive annelids have a pair of ventral nerve cords joined by transverse connectives; the most advanced forms have the cords fused to form a single cord. A ganglionic swelling of the cord is found in each body segment, with the most anterior ganglion, the subpharyngeal ganglion, being the most prominent.

9. Segmented Nervous system of Earthworm Earthworm has a well-developed nervous system . The nervous system is metamerically segmented. The nervous system is divisible into central, peripheral and autonomic nervous system (sympathetic nervous system).

10. Central nervous system of earthworm : It includes a nerve ring and a nerve cord

11. Nerve ring of earthworm : Nerve ring is an oblique ring around the pharynx in 3rd and 4th segments. Its mid-dorsal part comprises of a pair of small and fused supra-pharyngeal ganglia, also called cerebral ganglia or brain.

12. Nerve cord in Earthworm : Nerve cord is surrounded by epineurium (a common sheath of connective tissue ). Outside epineurium , there is a layer of longitudinal muscle fibers. This is finally surrounded by a layer of visceral peritoneum . Nerve cells are mainly present in ventral and lateral sides of the nerve cord . Nerve fibers are mainly present in dorsal and middle portion of nerve cord.

13. Peripheral nervous system (PNS) of earthworm: All nerves arise from CNS and supply to various parts of body . All the nerves present in earthworm are of mixed type as they contain both afferent and efferent nerve fibres and adjustors (association neurons ). From the cerebral ganglia/brain, 8-10 pairs of nerves arise.

14. Autonomic nervous system (ANS) of earthworm: ANS of Pheretima posthuma possess sympathetic nervous system only with extensive nerve plexus that are connected to the nerves from circum-pharyngeal connectives.

15. Nervous activities in Earthworm : All earthworm operations are regulated by the nervous system, but not necessarily by the brain . They have both sensory and motor neurons, like larger animals.Sensory fibers start in the epidermis from sensory cells or receptor organs and end in fine branches in the ventral nerve cord.

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