Placode

Placode

A placode is an area of thickening in the embryonic epithelial layer where some organ or structure later develops. The term usually refers to cranial placodes, peripheral nervous system structures associated with the special senses and cranial ganglia. Placodes also develop in the formation of other structures, such as teeth and feathers.

Cranial Placodes

The placodes associated with the special senses are:

* The "Adenohypophyseal placode"

* The "otic placode" forms the otic pit and the otic vesicle, giving rise eventually to organs of hearing and equilibrium.

* The "lens placode" under the direction of the optic vesicle gives rise to the lens of the eye.

* The "olfactory placode" (or "nasal placode" [EmbryologyUNC|hednk|027] ) gives rise to the olfactory epithelium of the nose.

* The "trigeminal placode" consists of opthalmic and maxillomandibular parts.

* The "epibranchial placodes" consist of the geniculate, petrosal, and nodose placodes.

Non human species

* The "lateral line placodes" (in aquatic vertebrates) give rise to the lateral line system.

* The "profundal placodes"

References


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  • placode — [plakɔd] n. f. ÉTYM. XXe; de placo , et du grec eidos « forme ». ❖ ♦ Embryol. Chacun des épaississements de l ectoderme dont dériveront les organes des sens et les ganglions nerveux. || Placode auditive, olfactive, optique …   Encyclopédie Universelle

  • placode — Local thickening in the embryonic ectoderm layer; the cells of the p. ordinarily constitute a primordial group from which a sense organ or ganglion develops. [G. plakodes, fr. plax, anything flat or broad, + eidos, like] auditory placodes SYN:… …   Medical dictionary

  • placode — ˈplaˌkōd noun ( s) Etymology: International Scientific Vocabulary plac + ode : a platelike thickening of embryonic ectoderm from which a definitive structure develops ear placode olfactory placode see lens placode …   Useful english dictionary

  • placode — a thickened or plate like region within an epithelium …   Dictionary of ichthyology

  • placode — Area of thickened ectoderm in the embryo from which a nerve ganglion, or a sense organ will develop …   Dictionary of molecular biology

  • placode — /plak ohd/, n. Embryol. a local thickening of the endoderm in the embryo, that usually constitutes the primordium of a specific structure or organ. [1905 10; < Gk plak (s. of pláx) something flat, tablet + ODE1] * * * …   Universalium

  • placode — noun A platelike thickening of the epithelial layer of an embryo from which an organ, especially a sense organ, develops …   Wiktionary

  • placode — pla·cò·de s.m. TS embriol. nei Vertebrati, ispessimento discoidale dell ectoderma, nella zona cefalica dell embrione, da cui derivano gli organi sensoriali {{line}} {{/line}} DATA: 1958. ETIMO: dal gr. plakōdēs piatto …   Dizionario italiano

  • placode — pl.m. placodi …   Dizionario dei sinonimi e contrari

  • placode — n. thickening of endodermic tissue, initial stage in organ formation (Embryology) …   English contemporary dictionary

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