From the Research
The development of the human ear occurs in a systematic process throughout embryonic and fetal development, with key milestones including the formation of otic placodes around week 3, invagination to form otic vesicles by week 4, and the development of inner, middle, and external ear structures over subsequent weeks. The ear begins forming around week 3 of gestation when thickenings called otic placodes appear on either side of the hindbrain 1. By week 4, these placodes invaginate to form otic vesicles, which will develop into the inner ear structures. During weeks 5-6, the cochlear duct begins to coil, and the semicircular canals start forming from the vestibular portion of the otic vesicle. The middle ear begins developing around week 4 from the first pharyngeal pouch, with the auditory ossicles (malleus, incus, and stapes) deriving from the first and second pharyngeal arches between weeks 6-8 2. The external ear develops from six hillocks that appear around the first pharyngeal cleft during weeks 6-7, gradually fusing to form the auricle. By week 8, the external auditory canal is forming, and by week 16, the inner ear reaches adult size. The tympanic membrane forms where the external auditory canal meets the middle ear cavity around weeks 8-10. The entire ear structure continues to mature throughout pregnancy, with the external ear reaching near-final position by week 20, though hearing function begins around weeks 24-25 when the cochlea becomes functional and the fetus starts responding to sounds. Key features of ear development include:
- Formation of otic placodes around week 3
- Invagination to form otic vesicles by week 4
- Development of inner ear structures, including the cochlear duct and semicircular canals, during weeks 5-6
- Development of middle ear structures, including the auditory ossicles, between weeks 6-8
- Development of external ear structures, including the auricle and external auditory canal, during weeks 6-7 and beyond.