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Under a Creative Commons license Open access AbstractIt has been long considered that air and bone are the two major mediators that conduct sounds to the inner ear. In 2004, Hosoi found that vibration of aural cartilage, generated by placing gently a transducer on it, could create audible sound with the same level of clarity as air- and bone-conduction sound. He thus proposed the term “cartilage conduction” for this concept. This research identified a third mediator for sound conduction to the inner ear. Hosoi also proposed the development of novel communication devices, such as hearing aids, telephones, etc. using his findings. For cartilage conduction, three sound pathways can be assumed. The transducer vibration may cause airborne sound which passes into the external auditory canal through the canal entrance (direct air pathway). Alternatively, the vibration at the cartilage may generate audible sound in the external auditory canal (cartilage-air pathway), or propagate directly to the inner ear through the skull bone (cartilage-bone pathway). A series of studies has illustrated that the cartilage-air pathway is dominant for hearing sensations in listeners with normal ears. The cartilage-bone pathway works for patients with bony aural atresia. A fourth pathway, the fibrotic-tissue pathway, is considered to act in the case of fibrotic aural atresia. In this review, we summarize this series of studies and discuss the nature of cartilage conduction. KeywordsCartilage conduction Sound transmission pathway Atresia of the external auditory canal Hearing aid Smart phone Cited by (0)© 2019 The Authors. Published by Elsevier B.V. The human ear can be divided into three sections. Each section performs a different role in transmitting sound waves to the brain.
View the diagrams below to learn more about the different sections of the ear and how we hear. Parts of the Outer EarThe outer ear consists of the visible portion on the side of the head, known as the pinna [1], and the external auditory canal (ear canal) [2]. The purpose of the pinna is to catch sound waves, amplify them slightly, and funnel them down the ear canal to the tympanic membrane (eardrum) [3]. The tympanic membrane is a very thin structure that separates the outer ear canal from the middle ear space.
Parts of the Middle EarThe middle ear is an air-filled cavity that sits between the tympanic membrane [3] and the inner ear. The middle ear also consists of three tiny bones called ossicles [4], the round window [5], the oval window [6], and the Eustachian tube [7]. Ossicles and Their Function
One end of the malleus is attached to the tympanic membrane and the other end is attached to the incus. The incus is attached to the stapes. The base of the stapes is located in a depression called the oval window [6]. The oval window membrane is one of two membranes that separate the middle ear space from the inner ear. The other is the round window membrane. The Eustachian tube [7] connects the middle ear space to the upper part of the throat. In its normal state, the Eustachian tube stays closed, but it will open when you yawn, swallow, chew, or hold your nose and blow. The purpose of the Eustachian tube is to provide fresh air to the middle ear space and to equalize pressure between the outer ear and the middle ear. Ever wonder why your ears “pop” when you go up or down in an airplane or an elevator in a tall building? That sound is your Eustachian tube(s) opening and closing to equalize the air pressure in your ears.
Parts of the Inner EarThe inner ear is encased in the temporal bone [8] and consists of three parts:
Parts of the CochleaThe cochlea is made up of three compartments (scala tympani, scala media, scala vestibuli) that are separated from each other by two membranes (basilar membrane and Reissner’s membrane). A tiny organ (organ of Corti) sits on top of the basilar membrane. This organ contains hair cells, which convert the mechanical energy from the vibrations of the basilar membrane into electrical impulses. Those electrical impulses are sent to the auditory nerve [12], which transmits the information up the brainstem to the auditory cortex. How We HearThe pinna catches sound waves and channels them down the external auditory canal, where they hit the tympanic membrane and make it vibrate. Those vibrations cause the three ossicles to move. The stapes footplate pushes on the oval window membrane, which sets the cochlear fluid in motion. This wave-like motion causes the basilar membrane to vibrate. As the basilar membrane moves up and down, the tiny “hairs” (stereocilia) on top of the hair cells open and close to change the electrical charge of the cell. This results in a release of chemicals (neurotransmitter), which signals auditory nerve fibers to fire. The auditory nerve sends these impulses up to the brain, where the signal is interpreted as sound.
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The transmission of sound waves through the external ear and the middle ear is known as
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