THE HUMAN EAR

E.A.R. is Excellent Acoustic Reader and sound waves travel through the outer ear, are modulated by the middle ear and are transmitted to the vestibulocochlear nerve in the inner ear. This nerve transmits information to the temporal lobe of the brain, where it is registered as sound. A sound that travels through the outer ear impacts on the tympanic membrane (ear drum) and causes it to vibrate. The three ossicles transmit this sound to a second window (the oval window) which protects the fluid-filled inner ear. In detail, the pinna of the outer ear helps to focus a sound, which impacts on the tympanic membrane. The malleus rests on the membrane and receives the vibration. This vibration is transmitted along the incus and stapes to the oval window. Two small muscles, the tensor tympani and stapedius, also help modulate noise. The tensor tympani dampens noise and the stapedius decrease the receptivity to highfrequency noise. Vibration of the oval window causes vibration of the endolymph within the ventricles and cochlea. The hollow channels of the inner ear are filled with liquid and contain a sensory epithelium that is studded with hair cells. The microscopic "hairs" of these cells are structural protein filaments that project out into the fluid. The hair cells are mechanoreceptors that release a chemical neurotransmitter when stimulated. Sound waves moving through fluid flows against the receptor cells of the Organ of Corti. The fluid pushes the filaments of individual cells; movement of the filaments causes receptor cells to become open to the potassium-rich endolymph. This causes the cell to depolarize and creates an action potential that is transmitted along the spiral ganglion, which sends information through the auditory portion of the vestibulocochlear nerve to the temporal lobe of the brain. The human ear can generally hear sounds with frequencies between 20 Hz and 20 kHz. Although hearing requires an intact and functioning auditory portion of the central nervous system as well as a working ear, human deafness (extreme insensitivity to sound) most commonly occur because of abnormalities of the inner ear, rather than in the nerves or tracts of the central auditory system. Sound below 20 Hz is considered infrasound, which the ear cannot process. It has been proven that the use of mobile phones increases the risk of acquiring cancer. This is due to the emission of electromagnetic radiation, the electromagnetic radiation makes their way through the ear and cause thermal heating to the most parts of the brain by degradation of DNA strands at that particular region. These radiation waves cause various cancers such as glioma, meningioma and acoustic neuroma.

The Outer Ear Transmits sounds to the tympanic membrane. The pinna collects sounds and channels it into the ear canal. The ear canal absorbs little sound but directs it to the drum head at its base. The tympanic membrane separates the ear canal from the middle ear and is the first part of the sound transducing mechanism. Shaped somewhat like a loudspeaker cone. The Middle Ear Is an air files space connected to the back of the nose by a long thin tube called the Eustachian Tube. The middle ear space house three little bones: the hammer (malleus), anvil (incus) and stirrup (stapes), which conduct sound from the tympanic membrane to the inner ear. The outer and middle ear are sound conducting mechanism. The Inner Ear • Structure: it is a shaped like snail shell it has two and a half turns and houses the organ of hearing known as the membranous labyrinth surrounded by fluid called the perilymph, this fluid is essentially incompressible. The membranous labyrinth is filled up with perilymph and endolymph, the both separate. • Function: Transduction of vibration in the audible range to a nervous impulse is performed by the inner hair cells; when the basilar membrane is rocked by a travelling wave, ion passages are opened or closed in the body of the cell and the afferent nerve ending which is attached to the hair cell base is stimulated. The cochlea is thus a remarkably efficient frequency analyzer. THE PHYSIOLOGY OF HEARING The Outer and Middle Ears The range of audible sound is approx. 10 octaves from somewhere between 16 and 32 Hz to somewhere between 1600 and 2000 Hz. The pinna catches higher frequency sounds and funnels them into the ear canal. The ear canal act as a resonating tube and actually amplifies sounds between 3000 and 4000 Hz. The ear is very sensitive and responds to sound of very low intensity to do this air pressure on both sides of the tympanic membrane most be equal. The Eustachian tube provide the means of the pressure equalization.

Otorhinolaryngology, Head and Neck Surgery, 2010

Page 1. 105 1.6 Inner Ear Andreas Arnold, Wolfgang Arnold, Roberto Bovo, Uwe Ganzer, Karl-Friedrich Hamann, Salvatore Iurato, Jan Kiefer, Kerstin Lamm, Walter Livi, Alessandro Martini and Gerard M.O' Donoghue 1.6.1 Zoster Oticus Salvatore Iurato and Wolfgang Arnold ...

The hearing system, also called also the auditory system, consists of the outer ear, middle ear, inner ear, and central auditory nervous system. The overall function of the hearing system is to sense the acoustic environment thus allowing us to detect and perceive sound. The anatomy of this system has been described in Chapter 8, Basic Anatomy of the Hearing System. The current chapter describes the function and physiology of the main parts of the hearing system in the process of converting acoustic events into perceived sound. In order to facilitate perception of sound, the hearing system needs to sense sound energy and to convert the received acoustic signals into the electro-chemical signals that are used by the nervous system. A schematic view of the processing chain from the physical sound wave striking the outer ear to the auditory percept in the brain is shown in Figure 9-1. Figure 9-1. A schematic view of the hearing system. The hearing system shown in Figure 9-1 has two functions: sound processing and hearing protection. Sound processing by the hearing system starts when the sound wave arrives at the head of a person. The head forms a baffle that reflects, absorbs, and diffracts sound prior to its processing by the hearing system. The first two sound processing elements of the hearing system are the outer and middle ears that form together a complex mechanical system that is sensitive to changes in intensity, frequency, and direction of incoming sound. Acoustic waves propagating in the environment are diffracted, absorbed, and reflected by the listener's body, head, and the pinnae and arrive through the ear canal at the tympanic membrane of the middle ear. After the acoustic wave strikes the eardrum, its acoustic energy is converted into mechanical energy and carried across the middle ear. At the junction of the middle ear and the inner ear, the mechanical energy of the stapes is transformed into the motion of the fluids of the inner ear and thence into the vibrations of the basilar membrane. The motion of the basilar membrane affects electro-chemical processes in the organ of Corti and results in generation of electric impulses by the array of the hair cells distributed along this membrane. The electrical impulses generated by the hair cells affect the inputs to the nerve endings of the auditory nerve and are transmitted via a network of nerves to the auditory cortex of the brain where the impulses are converted into meaningful perception. A secondary function of the hearing system is to provide some protection for the organ of Corti and the physical structures of the middle ear from excessive energy inputs and subsequent damage by modulating the 9

Journal of Basic and Clinical Physiology and Pharmacology, 2003

In a number of recently conducted animal studies, the effect of various external factors such as ototoxic substances, different types of noise and systemic disease on the different end-organs of the inner ear has been investigated. These studies are distinguished by the use of short latency vestibular evoked potentials (VsEPs) (to both linear and angular acceleration), an objective method for directly assessing the function of the different vestibular end-organs. In addition, the well known auditory brainstem response (ABR) was used to assess cochlear function. The studies are reviewed and it appears that the general pattern of effect is as follows: ABR (cochlea) is the most sensitive to the various external factors; angular VsEPs (semicircular canals) the least sensitive; linear VsEPs (otolith organs) intermediate between them.

Disease-a-Month, 2013

Scientific Reports

The human inner ear contains minute three-dimensional neurosensory structures that are deeply embedded within the skull base, rendering them relatively inaccessible to regenerative therapies for hearing loss. Here we provide a detailed characterisation of the functional architecture of the space that hosts the cell bodies of the auditory nerve to make them safely accessible for the first time for therapeutic intervention. We used synchrotron phase-contrast imaging which offers the required microscopic soft-tissue contrast definition while simultaneously displaying precise bony anatomic detail. Using volume-rendering software we constructed highly accurate 3-dimensional representations of the inner ear. The cell bodies are arranged in a bony helical canal that spirals from the base of the cochlea to its apex; the canal volume is 1.6 μL but with a diffusion potential of 15 μL. Modelling data from 10 temporal bones enabled definition of a safe trajectory for therapeutic access while pr...

Biomimetics

The design of the human ear is one of nature’s engineering marvels. This paper examines the merit of ear design using axiomatic design principles. The ear is the organ of both hearing and balance. A sensitive ear can hear frequencies ranging from 20 Hz to 20,000 Hz. The vestibular apparatus of the inner ear is responsible for the static and dynamic equilibrium of the human body. The ear is divided into the outer ear, middle ear, and inner ear, which play their respective functional roles in transforming sound energy into nerve impulses interpreted in the brain. The human ear has many modules, such as the pinna, auditory canal, eardrum, ossicles, eustachian tube, cochlea, semicircular canals, cochlear nerve, and vestibular nerve. Each of these modules has several subparts. This paper tabulates and maps the functional requirements (FRs) of these modules onto design parameters (DPs) that nature has already chosen. The “independence axiom” of the axiomatic design methodology is applied ...

La surdité brusquement installée est une urgence médicale nécessitant des investigations cliniques et paracliniques immédiates, ainsi qu’un traitement approprié et rapidement installé. L’hypoacousie brusque est invalidante pour le patient et sa permanence a des implications sur la qualité de vie de celui-ci. Conformément aux données de la littérature, la précocité du début du traitement est directement corrélée aux résultats thérapeutiques. La réponse à la thérapie est individuelle en raison des particularités anatomiques: le terrain vasculaire individuel, la vascularité pauci-immune et la fragilité de la vascularité cochléaire, ainsi que l’existence des malformations. La connaissance des mécanismes physiopathologiques de l’ischémie cérébrale a conduit à un nouveau paradigme dans les protocoles thérapeutiques modernes pour les micro-accidents vasculaires cérébraux ischémiques aigus et aggravés : les facteurs de croissance nerveuse. Les facteurs de croissance nerveux représentent une...