Finite element modelling of sound transmission from outer to inner ear

Abstract

The ear is one of the most complex organs in the human body. Sound is a sequence of pressure waves, which propagates through a compressible media such as air. The pinna concentrates the sound waves into the external auditory meatus. In this canal, the sound is conducted to the tympanic membrane. The tympanic membrane transforms the pressure variations into mechanical displacements, which are then transmitted to the ossicles. The vibration of the stapes footplate creates pressure waves in the fluid inside the cochlea; these pressure waves stimulate the hair cells, generating electrical signals which are sent to the brain through the cochlear nerve, where they are decoded. In this work, a three-dimensional finite element model of the human ear is developed. The model incorporates the tympanic membrane, ossicular bones, part of temporal bone (external auditory meatus and tympanic cavity), middle ear ligaments and tendons, cochlear fluid, skin, ear cartilage, jaw and the air in external auditory meatus and tympanic cavity. Using the finite element method, the magnitude and the phase angle of the umbo and stapes footplate displacement are calculated. Two slightly different models are used: one model takes into consideration the presence of air in the external auditory meatus while the other does not. The middle ear sound transfer function is determined for a stimulus of 60 dB SPL, applied to the outer surface of the air in the external auditory meatus. The obtained results are compared with previously published data in the literature. This study highlights the importance of external auditory meatus in the sound transmission. The pressure gain is calculated for the external auditory meatus.

Anatomy and Development of the Mammalian External Auditory Canal: Implications for Understanding Canal Disease and Deformity

“…With certain exceptions, the EAM is similar across all mammals; a deep-set structure on either side of the skull ending in an ear drum cul-de-sac medially and opening to a pinna laterally (Figure 1). In adult humans, the EAM is typically 25 mm in length and 8 mm in diameter (Areias et al, 2016). Rather than a horizontal tube its shape is that of a soft sigmoid, tilted to face downward and inward as it projects medially (van Spronsen et al, 2014).…”

“…This curved path varies between individuals (van Spronsen et al, 2014). Finite element modeling of the ear has highlighted the importance of a patent EAM in hearing higher frequency sound (which is crucial for speech recognition) (Areias et al, 2016). Lower frequencies with wavelengths larger than the canal itself are not affected by variations in canal diameter, however, as sound waves concertina at higher frequency, variations in canal dimension have a discernible effect on sound transmission.…”

Signaling in the Auditory System: Implications in Hair Cell Regeneration and Hearing Function

“…Sound is transmitted through vibration of air molecules until it reaches the auditory system (Breedlove et al, ; Dobrev et al, ). The shape of the ear is specifically designed to focus sound waves (Areias et al, ). When passing through the external ear, vibrations are transmitted from the air molecules to the ear drum, which in turn vibrates (Silverthorn, ).…”

A perspective on stem cell therapy for ear disorders

“…When sound waves contact the outer ear, they are funneled into a small area and cause vibrations on the tympanic membrane. The middle ear, composed of the tympanic cavity and ossicles, receive this mechanical signal that has been attenuated and transmit them to the inner ear, where it is converted into electrochemical signals by hair cells (HCs) (Areias, Santos, Natal Jorge, Gentil, & Parente, ). Tympanic membrane perforation (TMP) due to trauma or infection is one of the most common presentation of ear disorders that can cause hearing loss (Gaur, Sinha, Bhushan, & Batni, ).…”