Biomechanics of the middle ear

Abstract

Naslov završnog rada je "Biomehanika Srednjeg Uha". Ljudsko srednje uho je mehanički sustav za prijenos zvuka iz vanjskog u unutarnje uho. U početnom dijelu završnog rada govori se o anatomiji srednjeg uha. Detaljno su opisani dijelovi srednjeg uha: slušne koščice (čekić, nakovanj i stremen) i membrana bubnjića te njihova funkcija u ljudskom tijelu. Također ukratko je opisano vanjsko i unutarnje uho pošto su usko vezani za funkciju srednjeg uha. U nekoliko tablica iznesene su najvažnije dimenzije i mehanička svojstva djelova srednjeg uha. Iz literature su uzeti i pomaci membrane bubnjića na pragu sluha. Zvuk je naša percepcija podražaja nastalog kao poremećaj tlaka u mediju. Bubnjić vibrira pod utjecajem zvuka, a slušne koščice prestavljaju polužni sustav s nejednakim krakovima što uzrokuje povećanje zvučnog tlaka. U drugom dijelu rada govori se općenito o zvuku i načinu na koje naš mozak pomoću srednjeg i unutarnjeg uha interpretira zvuk. Pojašnjeni su neki osnovni pojmovi kao što su zvučni tlak, karakteristična impendancija i intenzitet zvuka koji su nužni za razumjevanje tematike. Prikazana je tablica u kojoj su pokazani različiti intenziteti zvuka koje možemo čuti u prirodi i okolišu. Domet ljudskog sluha seže kroz čak 12 redova veličine. U posljednjem dijelu rada se govori o izradi 3D modela pomoću metode konačnih elemenata. Srednje uho se prvo treba slikati HRCT metodom te se onda ti podaci (dimenzije i geometrija) ubacuju u računalo. Nakon toga se na računalu radi mreža konačnih elemenata za 3D model srednjeg uha.The title of this final thesis is „Biomechanics of the middle ear“. Human middle ear is a mechanical system for sound transfer from outer to inner ear. Anatomy of middle ear is described in first part of this thesis. Parts of middle ear, ossicular chain (malleus, incus, stapes) and eardrum membrane, are described in detail aswell as their function in the human body. Outer and inner ear are shortly described because of their close connection to middle ear. The most important dimensions and mechanical properties of the middle ear are given in several tables. Displacement of eardrum membrane on the minimum audible threshold are taken from literature [10]. Sound is our perception of stimulation which originates as disruption of pressure in medium. Eardrum vibrates under influence of sound, and ossicular chain represents leverage system with unequal handles which results in acustic pressure gain. Sound in general and the way our brain interpretates sound with help from inner and middle ear are described in second part of this thesis. Some of the basic terms which are necessary for understanding of this problem like acustic pressure, characteristic impendance and sound intesity are also described. There is a table with different sound intensities from our environment. Range of human hearing spans 12 orders of magnitude. One of the goals of this final thesis was to calculate forces on stapes footplate for minimum audible threshold (acustic pressure on eardrum membrane of 6 20 10 Pa ) and for normal speech level of 60 dB(acustic pressure on eardrum membrane of 3 25 10 Pa ). The force on stapes footplate for minimum audible threshold is 1 1,5 nNF and for normal speech level 2 1,95 nN F . This force figures show us incredible sensibility of human middle ear. Construction of 3D finite element model is discussed in the last part of this thesis. After HRCT scan of the middle ear, data (dimensions and geometry) is transfered to computer. After that finite element mesh is created for 3D middle ear model. Comparison of results from finite element analysis and experimental analysis are shown in figure 15. and 16