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BISC 219/2009: Mod 1 C. elegans General Information: Difference between revisions
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BISC 219/2009: Mod 1 C. elegans General Information (view source)
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== Nematode Anatomy == | == Nematode Anatomy == | ||
The hypodermal body wall of ''C. elegans'' is covered by an external cuticle composed primarily of modified forms of collagen. The body cavity (or pseudocoelom) is maintained at a high hydrostatic pressure relative to the outside, and this pressure on the elastic cuticle gives the animal rigidity and structural integrity. The hypodermis consists of four longitudinal ridges (dorsal, ventral, left and right lateral) joined circumferentially by thin sheets of cytoplasm which separate the muscle cells from the cuticle. The hypodermal cells secrete cuticular components and display a periodic activity associated with molting. The body muscles are organized into four longitudinal rows of 24 cells each, located between the hypodermal ridges. When the animal moves, the two subventral muscle strips are coordinated together, as are the two subdorsal strips, producing a sinusoidal wave motion in the dorsal-ventral plane. The alimentary canal includes a muscular pharynx, which takes up food (bacteria), grinds it, and pumps it into the intestine. The intestine consists of 30 to 34 cells; it is lined with microvilli leading to an anal sphincter valve that is operated by a pair of muscles.<br> | The hypodermal body wall of ''C. elegans'' is covered by an external cuticle composed primarily of modified forms of collagen. The body cavity (or pseudocoelom) is maintained at a high hydrostatic pressure relative to the outside, and this pressure on the elastic cuticle gives the animal rigidity and structural integrity. The hypodermis consists of four longitudinal ridges (dorsal, ventral, left and right lateral) joined circumferentially by thin sheets of cytoplasm which separate the muscle cells from the cuticle. The hypodermal cells secrete cuticular components and display a periodic activity associated with molting. The body muscles are organized into four longitudinal rows of 24 cells each, located between the hypodermal ridges. When the animal moves, the two subventral muscle strips are coordinated together, as are the two subdorsal strips, producing a sinusoidal wave motion in the dorsal-ventral plane. The alimentary canal includes a muscular pharynx, which takes up food (bacteria), grinds it, and pumps it into the intestine. The intestine consists of 30 to 34 cells; it is lined with microvilli leading to an anal sphincter valve that is operated by a pair of muscles.<br> | ||
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The nervous system of ''C. elegans'' consists of approximately 300 neurons, including a circumpharyngeal nerve ring, dorsal and ventral nerve cords, and a variety of sensory receptors and ganglia. About 70% of the neurons are located in the head. Sense organs (sensilla) are arranged in two concentric rings around the mouth and include both chemoreceptors and mechanoreceptors. ''C. elegans'' exhibits chemotaxis to a number of compounds. It also responds to a tap on the head by moving backwards, and then by turning to move forward.<br> | The nervous system of ''C. elegans'' consists of approximately 300 neurons, including a circumpharyngeal nerve ring, dorsal and ventral nerve cords, and a variety of sensory receptors and ganglia. About 70% of the neurons are located in the head. Sense organs (sensilla) are arranged in two concentric rings around the mouth and include both chemoreceptors and mechanoreceptors. ''C. elegans'' exhibits chemotaxis to a number of compounds. It also responds to a tap on the head by moving backwards, and then by turning to move forward.<br> | ||
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''C. elegans'' generally reproduces as a self-fertilizing hermaphrodite, with each animal producing BOTH sperm and eggs. Two reflexed gonadal arms (each of which contains an ovary, oviduct, spermatheca, and uterus) terminate at the vulva, located midway along the ventral side. The mature hermaphrodite is effectively a female because the gonad has earlier made and stored sperm before turning to the production of oocytes. Eggs (developing embryos) are fertilized by endogenous sperm and then undergo some development inside the parental hermaphrodite. Embryos are arranged along the uterus with the most developed ones nearest the vulva. Fertilized eggs are covered with a chitinous shell and, when mature enough, are deposited on the agar surface. The entire life cycle takes about 3 1/2 days at 20°C with each adult hermaphrodite producing 250-350 progeny.<br> | |||
== Nematode Lifecycle == | |||
The development of ''C. elegans'' is known in great detail because this tiny organism (1 mm in length) is transparent and the developmental pattern of all 959 of its somatic cells has been traced. ''C. elegans'' generally reproduces as a self-fertilizing hermaphrodite, with each animal producing BOTH sperm and eggs. Two reflexed gonadal arms (each of which contains an ovary, oviduct, spermatheca, and uterus) terminate at the vulva, located midway along the ventral side. The mature hermaphrodite is effectively a female because the gonad has earlier made and stored sperm before turning to the production of oocytes. Eggs (developing embryos) are fertilized by endogenous sperm and then undergo some development inside the parental hermaphrodite. Embryos are arranged along the uterus with the most developed ones nearest the vulva. Fertilized eggs are covered with a chitinous shell and, when mature enough, are deposited on the agar surface. Embryogenesis occurs in about 12 hours, development to the adult stage occurs in 2.5 days, and the worm's life span is 2-3 weeks. The entire life cycle takes about 3 1/2 days at 20°C with each adult hermaphrodite producing 250-350 progeny.<br> | |||
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[[Image:AnatomyLarge.gif]] | [[Image:AnatomyLarge.gif]] | ||
