![]() ![]() What factors determine the development of the ear canal’s specialized epithelium? And how does the canal integrate with the middle ear to form a functioning structure? Ear Canal Anatomy and Function As anatomical and molecular details are added to our understanding of ear development, compelling questions are beginning to emerge. We then turn to the congenital and acquired defects of the canal, and how they are currently treated, before investigating canal development. We discuss the anatomy of the canal and the epithelial dynamics involved in canal homeostasis. In this review we focus in on the ear canal or EAM. Management of hearing loss in this part of the ear may be particularly challenging, as the interaction between the anatomy and physiology of the canal, and the pathologies that affect it, may complicate the two most commonly used techniques of hearing rehabilitation – hearing aids and hearing restoration surgery. Pathologies of the ear canal can cause hearing loss, recurrent infection, and complications including cranial nerve palsy and intracranial sepsis ( Ostrowski and Wiet, 1996). This leaves the outer ear, which is also indispensable for hearing, but is comparatively overlooked. Currently, the clinician’s arsenal is best equipped to treat middle ear disease, which consequently receives the lion’s share of clinical attention ( Cunningham and Tucci, 2017). However, there are limited options for treating sensorineural hearing loss with many potential treatments in the experimental phase ( Devare et al., 2018). Hearing loss is most commonly caused due to pathology in the inner ear, referred to as sensorineural hearing loss, which consequently receives the lion’s share of scientific research ( Cunningham and Tucci, 2017). This intricate leverage mechanism corrects the impedance mismatch between gas and liquid allowing airborne sound waves to move hair cells in the fluid-filled cochlea, generating neural signals that are transmitted to the auditory cortex via the cochlear nerve. The middle ear ossicles connect the TM to the much smaller oval window of the inner ear. The pinna or auricle directs sound waves into the external auditory Meatus (EAM), which then funnels sound waves toward the ear drum or tympanic membrane (TM), causing it to displace and move the ossicular chain of bones in the air-filled middle ear. The mammalian ear is a crucial and fascinating sensory organ formed from the integration of three parts ( Figure 1). That we can “hear” these waveforms involves a complex array of neurophysiological mechanisms which begin at the outer ear and end at the auditory cortex. Sound is essentially a series of pressure waves in our airborne environment. Hearing places us within our external environment, allowing us to experience a multi-dimensional world, to listen and to communicate. ![]() Together this knowledge allows clinical questions to be approached from a developmental biology perspective. Here we review our current understanding of ear canal development how this biological lumen is made what determines its location and how its structure is maintained throughout life. Recent studies have built on decades-old knowledge of ear canal development and suggest a novel multi-stage, complex and integrated system of development, helping to explain the mechanisms underlying congenital canal atresia and stenosis. Defects in development, or later blockages in the canal, lead to congenital or acquired conductive hearing loss. Unique anatomical adaptations, such as its migrating epithelium and cerumen glands, equip the ear canal for its function as both a conduit and a cul-de-sac. Within our complex hearing pathway, the ear canal is responsible for funneling sound waves toward the tympanic membrane (ear drum) and into the middle ear, and as such is a physical link between the tympanic membrane and the outside world. This review focuses on the often-neglected outer ear, specifically the external auditory meatus (EAM), or ear canal. The mammalian ear is made up of three parts (the outer, middle, and inner ear), which work together to transmit sound waves into neuronal signals perceived by our auditory cortex as sound. 2Department of Paediatric Otolaryngology, Cochlear Implants, Great Ormond Street Hospital for Children NHS Trust, London, United Kingdom.1Centre for Craniofacial and Regenerative Biology, King’s College London, Guy’s Hospital, London, United Kingdom.Mona Mozaffari 1*, Robert Nash 2 and Abigail S. ![]()
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