Virtual ear dissection (embryology of the ear)

• The lens develops from a specialized thickening of ectoderm called a placode. These structures give rise to many sense organs of the head, in whole or in part, and are often neurogenic (ie they make cranial PNS neurones).

  otic for ears

  
• As well as neural crest there is specialized bits of skin that relate to special senses and can make neurons (called placodes)
• Ectodermal placodes are focal thickenings of the cranial ectoderm that generate many different components of the sensory systems of the head
• In neurogenic placodes cells adopt a neuronal rather than mesenchymal morphology as soon as they leave the placodal epithelium
• how many epibranchial placodes are there and what do they become?

  Epibranchial placodes (geniculate, petrosal, and nodose) lie more ventrally, and are associated with the dorsocaudal aspect of the pharyngeal clefts and give rise to viscerosensory neurons of the facial, glossopharyngeal, and vagal nerves.
• The 3 epibranchial placodes give rise to neurons that delaminate from the placodes and form the ganglia of the facial (VII), glossopharyngeal (IX), and vagus (X) nerves.
• the epibranchial placodes and the otic placode give rise to neurones
• The otic placode gives rise to neurons that delaminate from the placode and form the cochleovestibular ganglion of the vestibulocochlear nerve (VIII).