True regarding the development of ear: (PGI Dec 2007)
Ans: A (Eustachian tube..); B (Eustachian tube.,); C (Pinna develops..) & D (Growth of the inner,.) Eustachian Tubeit connects nasopharynx with the tympanic cavity. In adults it is about 36 cm long & runs downwards, forwards media] ly from its tympanic end, forming an angle of 45 with the horizontal.The tympanic end of the tube is body & is situated in the anterior wall of the middle ear. A little above the level of the floor. The pharyngeal end of the tube is slit-like & situated in the lateral wall of the nasopharynx, 1-1.25 cm behind the posterior end of the inferior turbinate.it develops from the first arch & partly from the second aarch -Dhingra 5th/14Development of EarInterna Ear It is the first part of the ear to develop Early in the 4th Meek (22 days), a thickening of surface ectoderm the otic placodes appear, which invaginate into underlying mesenchyme to form otic pit (27 days) and then otic or auditory vesicles (otocyst)- the primordium of membranous labyrinth (4.5 weeks Ventralsaccular component of otic vesicle gives rise to saccule & cochlear duct, whereas dorsal utricular part forms small endolymphatic duct, utricle & semicircular canals. Development of membranous internal ear is completed by the 16th week and reaches its adult size by 20-22 weeksQ, when the cochlea is developed sufficiently. Middle Ear Develops in 4 weeks. & competes at 30 week Tympanic cavity, eustachian tube, mastoid antrum & air cells develop from endoderm of first pharyngeal pouch3 The lateral end of pouch expands & forms a tubotympanic recess, which given rising to primitive tympanic cavity whereas the proximal part forms auditory (eustachian) tube. Malleus & incus a re-derived from mesoderm (cartilage) of 1 from 2 arch, except its footplate and annular ligament which are derived from the otic capsule.External Ear Tympanic membrane develops from all three germinal layers, i.e.* ectoderm of 1st pharyngeal cleft* mesenchyme of 1 & 2 pharyngeal arches* endoderm of 1 pharyngeal pouch (tubotympanic recess). External auditory meatus develops from dorsal portion of 1 pharyngeal groove (cleft) Meatal plug is formed at the beginning of 3rd month & dissolves in 7 months. Auricle (pinna) develops from 6mesenchymai proliferations at thedorsal ends of 1 & 2 pharyngeal arches - utricular hillocks - surrounding the first pharyngeal cleft-* Auricle begins to develop at the base of the neck in 6 weeks and assume the normal position at 32 weeks, as the mandible develops.
Eustachian tube opens at the level of inferior turbinate
Eustachian tube develops from the cleft of first arch
Pinna develops from the cleft of 1st arch
Growth of the inner-ear completed by 4tb month