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A platelike epithelial thickening, frequently marking, in the embryo, the anlage of an organ or part.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



the rudiment of a sense organ or ganglion in humans, vertebrates, and some invertebrates. Placodes are paired thickenings of the outermost embryonic germ layer, the ectoderm; they arise as the nervous system is laid down in the early stages of embryogeny. In vertebrates, placodes give rise to the olfactory organ, the crystalline lens of the eye, the inner ear, the auditory ganglion, and the ganglia of the facial, glossopharyngeal, and vagus nerves. In cyclostomes, fishes, and many amphibians, placodes give rise to the lateral-line organs in addition to the aforementioned structures.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
The otic vesicle is formed from the invagination of the otic placode. In a study investigating the conditions that influence the response to Fgf during otic placode induction (13), signaling of this factor has been shown to induce the expression of zebrafish otic genes such as pax8, pax2a, fgf24, and sox3 throughout the preplacodal region, which is important in setting the pattern of the otic vesicle.
Notch signaling also plays a role in specifying the sensory domains within the otic placode by inducing the proliferation of undifferentiated presensory cells, upregulating Sox2 activity, and inhibiting Ngn1 activity (19).
Pax2 transcripts were previously shown to be initially distributed uniformly throughout the epithelium of the otic placode [23].
The goal of the zebrafish research is to understand at the molecular level, how and why otic placode cells decide to become neuronal, non-sensory or sensory cells.
The main goal of the frog research is to determine which molecules and regions of the otic placode are required for normal patterning in the developing inner ear.