Placodes
Introduction
Placodes are ectodermal thickenings which have important roles in development of special sensory systems.
In human development, during week 4 a series of thickened surface ectodermal patches form in pairs rostro-caudally in the head region.
Recent research suggests that all sensory placodes may arise from common panplacodal primordium origin around the neural plate, and then differentiate to eventually have different developmental fates. (More? Schlosser G.) These sensory placodes will later contribute key components of each of our special senses (vision, hearing and smell).
Other species have a number of additional placodes which form other sensory structures (fish, lateral line receptor). Note that their initial postion on the developing head is significantly different to their final position in the future sensory system (More? Sensory Notes).
Otic placode - in the stage 13/14 embryo (shown below) the otic placode has sunk from the surface ectoderm to form a hollow epithelial ball, the otocyst, which now lies beneath the surface surrounded by mesenchyme (mesoderm). The epithelia of this ball varies in thickness and has begun to distort, it will eventually form the inner ear membranous labyrinth.
Optic placode - lies on the surface, adjacent to the outpocketing of the nervous system (which will for the retina) and will form the lens.
Nasal placode - has 2 components (medial and lateral) and will form the nose olefactory epithelium.
Some Recent Findings
- Epibranchial Placodes[1] "The inner ear and the epibranchial ganglia constitute much of the sensory system in the caudal vertebrate head. ...However, recent studies indicate that both systems arise from a morphologically distinct common precursor domain: the posterior placodal area. This review summarises recent studies into the induction, morphogenesis and innervation of these systems and discusses lineage restriction and cell specification in the context of their common origin."
- Otic Placode[2] "The inner ear epithelium, with its complex array of sensory, non-sensory, and neuronal cell types necessary for hearing and balance, is derived from a thickened patch of head ectoderm called the otic placode. ...Collectively, our results suggest that Wnt8a provides the link between FGF-induced formation of the pre-otic field and restriction of the otic placode to ectoderm adjacent to the hindbrain."
- Postotic Placode[3] "The (zebrafish) embryonic line originates from a postotic placode that produces both a migrating sensory primordium and afferent neurons. Nothing is known about the origin and innervation of the larval lines. Here we show that a "secondary" placode can be detected at 24 h postfertilization (hpf), shortly after the primary placode has given rise to the embryonic primordium and ganglion."
Sensory System
Embryo Week: Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 9
- Carnegie Stages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | About Stages | Timeline
References
Online Textbooks
- Developmental Biology (6th ed.) Gilbert, Scott F. Sunderland (MA): Sinauer Associates, Inc.; c2000. Chick embryo rhombomere neural crest cells | Some derivatives of the pharyngeal arches | Tissue Architecture of the Central Nervous System | Neuronal Types | Snapshot Summary: Central Nervous System and Epidermis
- Neuroscience Purves, Dale; Augustine, George J.; Fitzpatrick, David; Katz, Lawrence C.; LaMantia, Anthony-Samuel; McNamara, James O.; Williams, S. Mark. Sunderland (MA): Sinauer Associates, Inc. ; c2001 The Auditory System | The Inner Ear | Early Brain Development
- Clinical Methods 63. Cranial Nerves IX and X: The Glossopharyngeal and Vagus Nerves | The Tongue | 126. The Ear and Auditory System | An Overview of the Head and Neck - Ears and Hearing | Audiometry
- Eurekah Bioscience CollectionCranial Neural Crest and Development of the Head Skeleton
Search Bookshelf placode development
Reviews
<pubmed>20460364</pubmed> <pubmed>9927591</pubmed>
Articles
Search Pubmed
June 2010 "placode development" All (852) Review (90) Free Full Text (285)
Search Pubmed placode development | otic placode development | optic placode development | nasal placode development
Glossary Links
- Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link
Cite this page: Hill, M.A. (2024, June 15) Embryology Placodes. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Placodes
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G