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Evolution Of Nervous Systems
The evolution of nervous systems dates back to the first development of nervous systems in animals (or metazoans). Neurons developed as specialized electrical signaling cells in multicellular animals, adapting the mechanism of action potentials present in motile single-celled and colonial eukaryotes. Primitive systems, like those found in protists, use chemical signalling for movement and sensitivity; data suggests these were precursors to modern neural cell types and their synapses. When some animals started living a mobile lifestyle and eating larger food particles externally, they developed ciliated epithelia, contractile muscles and coordinating & sensitive neurons for it in their outer layer. Simple nerve nets seen in acoels (basal bilaterians) and cnidarians are thought to be the ancestral condition for the Planulozoa (bilaterians plus cnidarians and, perhaps, placozoans). A more complex nerve net with simple nerve cords is present in ancient animals called cteno ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nervous Systems
In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes that impact the body, then works in tandem with the endocrine system to respond to such events. Nervous tissue first arose in wormlike organisms about 550 to 600 million years ago. In vertebrates it consists of two main parts, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord. The PNS consists mainly of nerves, which are enclosed bundles of the long fibers or axons, that connect the CNS to every other part of the body. Nerves that transmit signals from the brain are called motor nerves or '' efferent'' nerves, while those nerves that transmit information from the body to the CNS are called sensory nerves or '' afferent''. Spinal nerves are mixed nerves that serve both fu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Planulozoa
Planulozoa is a clade which includes the Placozoa, Cnidaria (corals and jellyfish) and the Bilateria (all the more complex animals including worms, insects and vertebrates). The designation Planulozoa may be considered a synonym to Parahoxozoa. Within Planulozoa, the Placozoa may be a sister of Cnidaria to the exclusion of Bilateria. The clade excludes basal animals such as the Ctenophora Ctenophora (; ctenophore ; ) comprise a phylum of marine invertebrates, commonly known as comb jellies, that inhabit sea waters worldwide. They are notable for the groups of cilia they use for swimming (commonly referred to as "combs"), and ... (comb jellies), and Porifera (sponges). Although this clade was sometimes used to specify a clade of Cnidaria and Bilateria to the exclusion of Placozoa (against the original intention of its proposal), this is no longer favoured due to recent data indicating a sister group relationship between Cnidaria and Placozoa. The phylogenetic tree indi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Obelia
''Obelia'' is a genus of hydrozoans, a class of mainly marine and some freshwater animal species that have both polyp and medusa stages in their life cycle. Hydrozoa belongs to the phylum Cnidaria, which are aquatic (mainly marine) organisms that are relatively simple in structure with a diameter around 1mm. There are currently 120 known species, with more to be discovered. These species are grouped into three broad categories: ''O. bidentada'', ''O. dichotoma'', and ''O. geniculata''. ''O. longissima'' was later accepted as a legitimate species, but taxonomy regarding the entire genus is debated over. ''Obelia'' is also called sea fur. ''Obelia'' has a worldwide distribution except the high-Arctic and Antarctic seas. and a stage of ''Obelia'' species are common in coastal and offshore plankton around the world.Cornelius, P.F.S., 1995b. North-West European thecate hydroids and their Medusae. Part 2. Synopses of the British Fauna (New Series), No 50. ''Obelia'' are usually f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Multicellular
A multicellular organism is an organism that consists of more than one cell, in contrast to unicellular organism. All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially uni- and partially multicellular, like slime molds and social amoebae such as the genus ''Dictyostelium''. Multicellular organisms arise in various ways, for example by cell division or by aggregation of many single cells. Colonial organisms are the result of many identical individuals joining together to form a colony. However, it can often be hard to separate colonial protists from true multicellular organisms, because the two concepts are not distinct; colonial protists have been dubbed "pluricellular" rather than "multicellular". There are also multinucleate though technically unicellular organisms that are macroscopic, such as the xenophyophorea that can reach 20 cm. Evolutionary history Occurrence Multicellularity has evolved ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Action Potentials
An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and in some plant cells. Certain endocrine cells such as pancreatic beta cells, and certain cells of the anterior pituitary gland are also excitable cells. In neurons, action potentials play a central role in cell-cell communication by providing for—or with regard to saltatory conduction, assisting—the propagation of signals along the neuron's axon toward synaptic boutons situated at the ends of an axon; these signals can then connect with other neurons at synapses, or to motor cells or glands. In other types of cells, their main function is to activate intracellular processes. In muscle cells, for example, an action potential is the first step in the chain of event ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dorsal Nerve Cord
The dorsal nerve cord is a unique feature to chordates, and it is mainly found in the Vertebrata chordate subphylum. The dorsal nerve cord is only one embryonic feature unique to all chordates, among the other four chordate features-- a notochord, a post-anal tail, an endostyle, and pharyngeal slits. The dorsal hollow nerve cord is a hollow cord dorsal to the notochord. It is formed from a part of the ectoderm that rolls, forming the hollow tube. This is important, as it distinguishes chordates from other animal phyla, such as Annelids and Arthropods, which have solid, ventral tubes. The process by which this is performed is called invagination. The cells essentially convolute into the body cavity, arranging themselves on the dorsal plane above the notochord, as mentioned above. The evolutionary explanation to this adaptation from a solid cord to hollow tube is unknown. In vertebrates, the dorsal nerve cord is modified into the central nervous system, which comprises the brain and s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ventral Nerve Cord
The ventral nerve cord is a major structure of the invertebrate central nervous system. It is the functional equivalent of the vertebrate spinal cord. The ventral nerve cord coordinates neural signaling from the brain to the body and vice versa, integrating sensory input and locomotor output. Decapitated insects can still walk, groom, and mate, illustrating that the circuitry of the ventral nerve cord is sufficient to perform complex motor programs without brain input. Structure The ventral nerve cord runs down the ventral ("belly", as opposed to back) plane of the organism. It contains ascending and descending neurons that relay information to and from the brain, motor neurons that project into the body and synapse onto muscles, sensory neurons that receive information from the body and environment, and interneurons that coordinate circuitry of all of these neurons. Ventral nerve cord neurons are physically organized into neuromeres that process signals for each body se ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cephalization
Cephalization is an evolutionary trend in which, over many generations, the mouth, sense organs, and nerve ganglia become concentrated at the front end of an animal, producing a head region. This is associated with movement and bilateral symmetry, such that the animal has a definite head end. This led to the formation of a highly sophisticated brain in three groups of animals, namely the arthropods, cephalopod molluscs, and vertebrates. Animals without bilateral symmetry Cnidaria, such as the radially symmetrical Hydrozoa, show some degree of cephalization. The Anthomedusae have a head end with their mouth, photoreceptive cells, and a concentration of neural cells. Bilateria Cephalization is a characteristic feature of the Bilateria, a large group containing the majority of animal phyla. These have the ability to move, using muscles, and a body plan with a front end that encounters stimuli first as the animal moves forwards, and accordingly has evolved to contain many of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tree Of Life (biology)
The tree of life or universal tree of life is a metaphor, model and research tool used to explore the evolution of life and describe the relationships between organisms, both living and extinct, as described in a famous passage in Charles Darwin's ''On the Origin of Species'' (1859). Tree diagrams originated in the medieval era to represent genealogical relationships. Phylogenetic tree diagrams in the evolutionary sense date back to the mid-nineteenth century. The term phylogeny for the evolutionary relationships of species through time was coined by Ernst Haeckel, who went further than Darwin in proposing phylogenic histories of life. In contemporary usage, ''tree of life'' refers to the compilation of comprehensive phylogenetic databases rooted at the last universal common ancestor of life on Earth. Two public databases for the tree of life are ''TimeTree'', for phylogeny and divergence times, and the '' Open Tree of Life'', for phylogeny. Early natural classif ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups of organisms. These relationships are determined by Computational phylogenetics, phylogenetic inference methods that focus on observed heritable traits, such as DNA sequences, protein amino acid sequences, or morphology. The result of such an analysis is a phylogenetic tree—a diagram containing a hypothesis of relationships that reflects the evolutionary history of a group of organisms. The tips of a phylogenetic tree can be living taxa or fossils, and represent the "end" or the present time in an evolutionary lineage. A phylogenetic diagram can be rooted or unrooted. A rooted tree diagram indicates the hypothetical common ancestor of the tree. An unrooted tree diagram (a network) makes no assumption about the ancestral line, and does ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spongilla
Overview ''Spongilla'' is a genus of freshwater sponges with over 200 different species. Spongilla was first publicly recognized in 1696 by Leonard Plukenet and can be found in lakes, ponds and slow streams.''Spongilla'' have a leuconoid body form with a skeleton composed of siliceous spicules. They are sessile organisms, attaching themselves to hard substrate like rocks, logs and sometimes to ground. Using their ostia and osculum these sponges filter the water for various small aquatic organisms such as protozoans, bacteria, and other free-floating pond life. Sponges of the genus ''Spongilla'' partake in symbiotic relationships with green algae, zoochlorellae. The symbiotic zoochlorellae give the sponges a green appearance and without them they would appear white. ''Spongilla'' was used by John Hogg in the 19th century to attempt to justify a fourth kingdom of life. Reproduction Sponges are hermaphroditic organisms, producing both egg and sperm. Sperm is released from one ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Choanocyte
Choanocytes (also known as "collar cells") are cells that line the interior of asconoid, syconoid and leuconoid body types of sponges that contain a central flagellum, or ''cilium,'' surrounded by a collar of microvilli which are connected by a thin membrane. They make up the choanoderm, a type of cell layer found in sponges. The cell has the closest resemblance to the choanoflagellates which are the closest related single celled protists to the animal kingdom (metazoans). The flagellae beat regularly, creating a water flow across the microvilli which can then filter nutrients from the water taken from the collar of the sponge. Food particles are then phagocytosed by the cell. Anderson, D. (2001) ''Invertebrate Zoology'' Oxford University Press Location Choanocytes are found dotting the surface of the spongocoel in asconoid sponges and the radial canals in syconoid sponges, but they comprise entirely the chambers in leuconoid sponges. Function By cooperatively moving the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
