Sensory Syatem In Invertebrates Essay

8105 words - 33 pages

Introduction: vertebrates are distinguished from other groups of animals by certain characteristics, principally related to their spinal cords and nervous systems, namely, the presence of a dorsal notochord surrounded by mesodermal tissue, which gives rise to a vertebral column in adults of most species, and a tubular nervous system lying dorsal to the cord, concentrated in the midline, and very well developed at its cephalic end (cephalization). The extent and pathways of nervous system development differs between invertebrates and vertebrates, even though, in all animals that have a nervous system, it is derived predominantly from ectodermComparative embryology and anatomy have ...view middle of the document...

Segmentation (metamerization) appears. The central nervous system is ventral (bilateral ventral cords), has no cavity and localization of sensory cells seems to be responsible for the segmental concentration which forms the metameric gangliaTHE SUPERIOR AND ADULT ANNELIDS (nereis, Lumbricus): the central nervous system is still ventral (single cord and ganglia) without a cavity, and there is transverse concentration. The cerebral ganglia are specialized for vision and olfactionTHE HEMICHORDATES (enteropneusts): a dorsal tubular and a solid ventral nervous system. There is no cord, but there is a cephalodorsal diverticulum of the intestine corresponding to a dorsal nervous tube. The diverticulum is incompletely separated from the overlying ectoderm from which it is derivedTHE PROCHORDATES (Chephalochordata, Amphioxus): a dorsal cord and a dorsal tubular central nervous system entirely developed from dorsal ectoderm. A ventral system is no longer seen. The anterior vesicle represents a true rudimentary brainVertebrate nervous system (Chordata): mesoderm determines the development of the nervous system and sense organs. The appearance of mesoderm groups together the inductive capabilities and marks an important stage in the genesis of developmentTHE NERVOUS SYSTEM is relatively independent of the sensory organization. However, the eye and general sensory receptors, are directly derived from the nervous systemDuring evolution, relationships between the nervous system and the sense organs are modifie In invertebrates, the nervous system appears to be only an accessory structure to the sensory system. In vertebrates, the importance of the nervous system becomes so great that everything else is organized for it and around itIN VERTEBRATES SUCH AS FISH, the 5 neural vesicles presage the cephalization of the higher vertebrates. During the slow progression of evolution, the role of the prochordal plate becomes essential since, in humans, it induces brain formationAnimals respond to the messages they receive from the world aound them. Their reactions to the outside world depend on how the data collected from their surroundings are correctly coded into signals that can be received and processed by neurons in the brain. The sensory organs provide the only means of communication from the environment to the nervous system. Sensations arise when signals are detected by sensory receptor cells are transmitted through the nervous system to the designated part of the brain. Various organs and cells are designated to receive specific stimuli. The major categories of sensory reception addressed here are chemoreception, mechanoreception, and photoreception. What are the general properties of sensory reception and how are these messages transmitted to the central nervous system?Animals require a constant detection of information from their surroundings. Such information is the animal's link to the outside world. Sensory input is initially detected by sensory receptors....

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