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EarAss. Prof. Dr. Malak A. Al-yawer
Internal Ear
Otic placodes
The first indication of the developing ear can be found in embryos of approximately 22 days as a thickening of the surface ectoderm on each side of the rhombencephalon (otic placodes)
vesicles otic
Each otic placode soon invaginates into the under-lying mesenchyme and forms an otic pit. The edges of the otic pit soon come together and fuse to form an otic vesicle. The otic vesicle then loses its connection with the surface ectoderm
During later development, each vesicle divides into
Saccule
Saccule (Cochlear duct)
Scala tympani and Scala vestibuli
Mesenchyme surrounding the cochlear duct soon differentiates into cartilage. In the 10th week, this cartilaginous shell undergoes vacuolization, and two perilymphatic spaces, the scala vestibuli and scala tympani, are formed.
Vestibular membrane and Basilar membrane
The cochlear duct is then separated from the scala vestibuli by the vestibular membrane and from the scala tympani by the basilar membrane.
Spiral ligament and Modiolus
The lateral wall of the cochlear duct remains attached to the surrounding cartilage by the spiral ligament, whereas its median angle is connected to and partly supported by a long cartilaginous process, the modiolus, the future axis of the bony cochlea.
The inner ridge and the outer ridge
Initially, epithelial cells of the cochlear duct are alike. With further development, however, they form two ridges the inner ridge, the future spiral limbus, and the outer ridge.
Organ of Corti
Impulses received by this organ are transmitted to the spiral ganglion and then to the nervous system by the auditory fibers of cranial nerve VIII
Utricle and Semicircular Canals
Utricle and Semicircular Canals
Semicircular Canals
Whereas one end of each canal dilates to form the crus ampullare, the other, the crus nonampullare, does not widen Since two of the latter type fuse, however, only five crura enter the utricle, three with an ampulla and two without.
Crista ampullaris Maculae acusticae
Statoacoustic ganglion
Middle Ear
Tympanic Cavity and Auditory Tube
The tympanic cavity
Ossicles
Mastoid antrum
By 2 years of age, the mastoid cells are well developed and produce conical projections of the temporal bones, the mastoid processes. The middle ear continues to grow through puberty.
External Ear
External Auditory Meatus
The external auditory meatus
Eardrum or Tympanic Membrane
Auricle
develops from six mesenchymal proliferations at the dorsal ends of the first and second pharyngeal arches, surrounding the first pharyngeal cleft.
Auricle
Note that hillocks 1, 2, and 3 are part of the mandibular portion of the first pharyngeal arch and that the ear lies horizontally at the side of the neck. At this stage, the mandible is small.
Auricular hillocks
These swellings (auricular hillocks), three on each side of the external meatus, later fuse and form the definitive auricle.
Clinical Correlates
Deafness and External Ear Abnormalities
Congenital deafness
usually associated with deaf-mutism, may be caused by abnormal development of the membranous and bony labyrinths or by malformations of the auditory ossicles and eardrum. In the most extreme cases, the tympanic cavity and external meatus are absent.
External ear defects
Preauricular appendages and pits
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