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. It has been suggested that embryology be merged into this article or section. ... In zootomy, epithelium is a tissue composed of a layer of cells. ... The peripheral nervous system or PNS, is part of the nervous system, and consists of the nerves and neurons that reside or extend outside the central nervous system (the brain and spinal cord) to serve the limbs and organs, for example. ... In medicine, Special senses is the term used to describe the senses of vision, hearing, taste, and smell. ...

Cranial Placodes

The placodes associated with the special senses are:

• 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 nasal placode (or olfactory placode^[1]) gives rise to the olfactory epithelium of the nose.

The eyes begin to develop as a pair of diverticula from the lateral aspects of the forebrain. ... The olfactory epithelium is a specialized epithelial tissue inside the nasal cavity that is involved in smell. ... Human nose in profile A typical bulbous human nose Anatomically, a nose is a protuberance in vertebrates that houses the nostrils, or nares, which admit and expel air for respiration. ...

References

1. ^ Embryology at UNC hednk-027