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In embryology, the nasal placode (or olfactory placode [1]) gives rise to the olfactory epithelium of the nose. Two nasal placodes arise as thickened ectoderm from the frontonasal process . They give rise to the nose , the philtrum of the upper lip , and the primary palate .
Medial and lateral nasal processes shown on embryo. The medial nasal process (nasomedial) on the inner side of each nasal pit merge into the intermaxillary segment and form the upper lip, crest, and tip of the nose. [1] The medial nasal processes merge with the maxillary prominences.
The cranial placodes that have neurogenic potential (i.e. give rise to neurons) can be divided into two groups, the dorsolateral placodes and the epibranchial placodes. [1] dorsolateral placodes includes: The trigeminal placode, [3] which consists of ophthalmic and maxillomandibular parts, and gives rise to the cells of the trigeminal ganglion
The face and neck development of the human embryo refers to the development of the structures from the third to eighth week that give rise to the future head and neck.They consist of three layers, the ectoderm, mesoderm and endoderm, which form the mesenchyme (derived form the lateral plate mesoderm and paraxial mesoderm), neural crest and neural placodes (from the ectoderm). [1]
The nasal placodes are also known as the olfactory placodes. This development is induced by the ventral part of the forebrain. [ 48 ] [ 49 ] In the sixth week, the ectoderm in each nasal placode invaginates to form an indented oval-shaped pit, which forms a surrounding raised ridge of tissue. [ 49 ]
At the start of this process, the developing embryo has divided into many cells, forming a hollow ball called the blastula. The blastula is polar, and its two halves are called the animal hemisphere and vegetal hemisphere. It is the animal hemisphere will eventually become the ectoderm. [2]
In embryology, Carnegie stages are a standardized system of 23 stages used to provide a unified developmental chronology of the vertebrate embryo.. The stages are delineated through the development of structures, not by size or the number of days of development, and so the chronology can vary between species, and to a certain extent between embryos.
In the embryo, the nasal region develops from neural crest cells which start their migration down to the face during the fourth week of gestation. A pair of symmetrical nasal placodes (thickenings in the epithelium) are each divided into medial and lateral processes by the nasal pits