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embryology of ear8

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Information about embryology of ear8
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Published on March 6, 2013

Author: adilshan

Source: authorstream.com

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EMBRYOLOGY OF THE EAR: EMBRYOLOGY OF THE EAR Dr Zeeshan Ahmad M.S.(ENT,PGY1) Nalanda Medical College & Hospital, Patna Introduction: Introduction The ear comprises three distinct parts. External ear Middle ear Internal ear Each part embryologically different . INTERNAL EAR: INTERNAL EAR First seen at 22 weeks as Otic Placodes . Invaginate forming Otic Vesicle. Otic Vesicle divides Dorsal Utricle, SSC, endolymphatic duct Ventral  Saccule , Cochlear duct 22 days 4 weeks PowerPoint Presentation: Ventral  In the 6 th week saccule forms tubular outpocketing at its lower pole  COCHLEA Cochlea penetrates mesenchyme 2.5 turns in spiral manner by 8 weeks . PowerPoint Presentation: Mesenchyme surrounding cochlear duct differentiates into cartilage shell . At 10 th week undergoes vacuolization Scala Tympani (Basilar memb .) Scala Vestibuli (Vestibular memb .) Modiolus (medial) Spiral ligament ( lat ) ORGAN OF CORTI: ORGAN OF CORTI Epithelial cells of cochlear duct Inner ridge forms Spiral Limbus Outer ridge One inner hair cells Four outer hair cells Covered by Tectorial membrane attached to spiral limbus PowerPoint Presentation: Dorsal  In the 6 th week utricle forms flattened outpocketing s Central portions appose and then disappear  SSC One end widens  ampulla PowerPoint Presentation: During formation of the otic vesicle, a small group of cells breaks away from its wall and forms the statoacoustic ganglion. Also recieves cells from Neural Crest. Splits into cochlear & vestibular parts and supplies Organ of Corti and the vestibular apparatus respectively. MIDDLE EAR: Tympanic cavity Auditory tube Ossicles MIDDLE EAR PowerPoint Presentation: Beginning at week 4, the tubotympanic sulcus develops as an extension of the endodermal epithelium of the first pharyngeal pouch Distal part  primitive tympanic cavity Proximal part A uditory tube ( eustachian tube) PowerPoint Presentation: The expanding end of the tubotympanic sulcus comes into proximity with the medial aspect of the ectodermal first pharyngeal cleft, the primordial external auditory canal. Distal part  primitive tympanic cavity Proximal part A uditory tube ( eustachian tube) MASTOID: MASTOID Growth of the tympanic cavity into the mastoid portion of the temporal bone  Mastoid antrum The attachment of the sternocleidomastoid on the temporal bone  M astoid process . Although the development of the mastoid air cells begins in fetal life, full maturation does not occur until age 2. OSSICLES: OSSICLES Beginning sometime between weeks 4 and 7 , a condensation of neural crest ectoderm embedded within the mesenchyme begins to form the ossicles BROADLY speaking-------- M alleus and I ncus  first pharyngeal arch S tapes  s econd arch PowerPoint Presentation: Meckel’s cartilage , which is derived from the first pharyngeal arch Head of M alleus B ody of I ncus Reichert cartilage , which is derived from second arch Manubrium of M alleus long process of I ncus Suprastructure of S tapes PowerPoint Presentation: Development of the stapes footplate is induced by a depression on the otic capsule, the lamina stapedialis . This occurs between weeks 6 and 9. PowerPoint Presentation: Although the ossicles appear during the first half of fetal life, they remain embedded in mesenchyme until the eighth month , when the surrounding tissue dissolves. PowerPoint Presentation: When the ossicles are entirely free of surrounding mesenchyme, the endodermal epithelium connects them in a mesentery-like fashion to the wall of the cavity The supporting ligaments of the ossicles develop later within these mesenteries. EXTERNAL EAR: Auricle External Auditory Meatus Tympanic Membrane EXTERNAL EAR AURICLE: AURICLE The auricle develops from six mesenchymal proliferations at the dorsal ends of the first and second pharyngeal arches, surrounding the first pharyngeal cleft. AURICLE: AURICLE These swellings (auricular hillocks), three on each side of the external meatus, later fuse and form the definitive auricle. AURICLE: AURICLE These swellings (auricular hillocks), three on each side of the external meatus, later fuse and form the definitive auricle. PowerPoint Presentation: Initially , the external ears are in the lower neck region but with development of the mandible, they ascend to the side of the head at the level of the eyes. External Auditory Meatus: External Auditory Meatus The external auditory meatus develops from the dorsal portion of the first pharyngeal cleft. At the beginning of the third month, epithelial cells at the bottom of the meatus proliferate, forming a solid epithelial plate, the meatal plug. PowerPoint Presentation: In the seventh month, this plug dissolves, and the epithelial lining of the floor of the meatus forms the definitive eardrum. At the beginning of the third month, epithelial cells at the bottom of the meatus proliferate, forming a solid epithelial plate, the meatal plug. TYMPANIC MEMBRANE: TYMPANIC MEMBRANE The eardrum is made up of ectodermal epithelial lining at the bottom of the auditory meatus, endodermal epithelial lining of the tympanic cavity, and intermediate layer of connective tissue . Derangement of development: Derangement of development There an exhausting list of disorders. lets name a few. Treacher collins Pendred Crouzon Preauricular sinus Treacher Collins: Treacher Collins Atresia of external auditory canal malformed auricle Middle and inner ear anomalies Downward slanting eyes Micrognathia Underdeveloped zygoma . Drooping of part of the lateral lower eyelids Pendred Syndrome: Pendred Syndrome Sensorineural deafness Widened vestibular aqueduct Shortened cochlea Crouzon’s disease: Crouzon’s disease Atresia of external auditory canal Malformation of ossicles Fusion of different sutures leads to different patterns of growth of the skull. Congenital Preauricular Sinus: Congenital Preauricular Sinus Failure of fusion of first and second arch tubercles THANK YOU: THANK YOU adilshan@gmail.com

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