Anatomy N Phs Of Ear

Anatomy and Physiology of the EAR PRO. XU Qiang

Dr.

Now, I introduce the anatomy of the ear.The Otology is researched into hearing and balance system. The hearing and balance system comprise the peripheral receptor apparatus,nervous pathways and the centers that is in the central nervous system.

一

External Ear

It consists of 1.auricle. 2.external auditory

meatus.

The auricle The auricle consists of cartilage,skin.The cartilage is an elastis cartilage. It is a framework covered by skin . Firstly the skin adheres tightly to perichondrium on the anterior surface,

secondly the skin is more loosely

attarched

posteriorly. For this reason when anterior surface of auricle is contusioned ,It often lead to detachment of the skin-perichondrial layer and

the formation of a

hematoma. painful.

It

is

very

The exeternal meatus The exeternal meatus is about 3 cm long , but the Chinese external meatus is about 2.5cm. I think the Chinese body is shorter than the American .

The external cannal consists of an outer cartilaginous part and inner bony part. The cartilaginous meatus is curved and lies at an angle to the bone part. Beyond it is TM(tympanic membrane)

二

Middle Ear

The middle ear consists of (1) Eustachian tube (2) Tympanic cavity (3) Tympanic antrum (4)Mastoid process

1.

The Eustachian tube

There is the Eustachian tube on the anterior wall of middle ear. It consists of cartilaginous portion (2/3)suspended from the skull base and bony portion (1/3). The bony portion together with the tensor tympani muscle forms the musculotubal cannal in the temporal bone.

This cannal lies adjacent to the internal carotid artery. The funnel-shaped pharyngeal ostium of the cartilaginous part (torus tubarius) lies in the nasopharynx. The bony end opends into the middle ear.

The junction between the two parts of the tube is very narrow. This is the site of predilection for inflammatory stenosis of the tube. The tube serves to equalize the pressure between the middle ear and nasopharynx and thus to equalize the pressure on each side of the tympanic membrane.

An increase in pressure in the tympanic cavity is usually compensated for passively via the Eustachian tube to the nasopharynx, whereas a decrease in pressure usually requires active ventilation from the nasopharynx along the tube to the middle ear cavity.

The tube opens and close in response to movements of the neighboring muscles and difference of air pressure between the nasopharynx and middle ear cavity which tend to equalize spontaneously. The principal closing mechanism is the elastic recoil of the cartilage of the tube and vavular action of the pharyngeal ostium of the tube. The tube is opened by contraction of the tensor palati and levator palati muscles.

2. Tympanic cavity. (1)Epitympanum (2)Mesotympanum (3)Hypotympanum

Ossicular Chain There are three small bones (a) malleus (b) incus (c) stapes. These are togther connected by ligment. The cavity just like a square box, there are six faces [1 Lateral wall. 2 inner lateral wall. 3 The posterior wall. 4 anterior wall. 5 superior wall. 6 basic wall. ]

<1>Lateral wall: outer lateral wall is tympanic membrane that consists of pars tensa and the pars flaccida. The pars tensa forms the stiff vibrating surface of the membrane and is attached to a fibrous ring lying in the tympanic sulcus of tympanic part of the temporal bone.

The pars tensa consists of three layers: the epithelial layer (outer epidermal layer) and middle ear mucosa (inside face) and middle firbrous layer. The middle firbrous of the pars tensa has an external radial layer of fibrous and an internal circular layer.

The pars flaccida is that part of the membrace in the area of the tympanic notch of Rivini. The pars flaccide of TM consista of two layers, outer face is epithelial layer, inter face is mucosa.

The annulus fibrosus forms a thickening of the edge of the tympanic membrane and is formed by both layers of fibers. The pars flaccide lacks the characteristic radialcircular structure which provides the normal pars tense with the necessary function tension.

Inner lateral Wall <2>The inner lateral wall of the middle ear also forms the lateral wall of the labyrinthine capsule.There are as following: a. Promontory at the basal turn of cochlea .

b. Above is the oval window niche with the stapes whose footplate is held loosely in the oval window by the annular ligament. The long process of the incus forms a joint with the stapes.

c The round window lies below the pyramidal eminence . d The bone facial nerve canal run inferior to the horizontal semicircular canal. e The horizontal semicircular .

The posterior wall: •

Pneumatic

system

of

the

temporal bone. This is the aircontaining cell of the mastoid process. There is a antrum that is a biggest air-containing cell.

<4>The anterior wall There are ostium of the Eustachian tube and the internal carotid artery. <5>The superior wall It is a bone plate of the temporal bone(The superior of the bone is brain of temporal leaf)

<6>The basic wall The basic wall of

the middle ear cavity is a bone plate. Glomus jugulare is under the bone plate .

Tympanic Antrum

Mastoid Process 1. Sinodural angle 2. Sigmoid sinus 3. Cells of the mostoid process

三 . The Inner Ear It is peripheral hearing and balance organs. The inner ear or labyrinth embedded in the temporal bone. The inner ear include: <1>Vestibular and semicircular canals. <2>Cochlear

The The labyrith can also be divided into a bony and membranous part. The first is formed by the labyrinthine capsule .

Labyrith

The round and oval windows form the bony and membranous openings to the labyrinth from the middle ear cavity, closed, respectively, by the stapes footplate and round window membrane.

Membranous Labyrinth Membranous labyrinth encloses a hollow system filled with endolymph. This passes via the endolymphatic duct to end in a blind sac, the saccus endolymphatics lying in the epidural space on the posterior surface or the petrous pyramid close to the sigmoid sinus.

The perilymphatic system forms a hollow space consisting of intercommunicating intercellular clefts communicating directly with the subarachnoid space via the cochlear aqueduct. Perilymph separates the membrane labyrinth from the internal. Layer of the labyrinthine capsule surroundine the various space.

Furthermore, the perilymphatic system communicate with the lymphatic clefts of the middle ear so that exchange of metabolites and fluid can occur between the middle and internal ear due to a hydrostatc pressure gradient. The cochlear aqueduct and endolymphatic ducts end in the jugular foramen .

The perilymph is the immediate substrate of the cochlear and vestibular sensory cells. It is formed partly by filtration from the blood and partly by diffusion of cerebrospinal fluid. The endolymph is a filtrate of perilymph, but its concentration of sodium and potassium is completely different.

the

endo-and-perilymphatic

space with potassium-sodium ion exchange in the saccus endolymphaticus. Functional disturbance of this electrolyte regulation system lead to a disorder of the inner ear known as Menieres disease

Vestibular-Semicircular canal system The balance mechanism is shown. It consists of the utricle and saccule enclosing the static macular with the sensory end organs for the reception They consists of supporting cells and hair cells .

On their surface lie the otoliths which consist of rhomboid calcium carbonate crystals. Linear acceleration change the otolith pressure and thus deflects the sensory hairs. This stimulates the sensory cell by alteration of resting potential.

Vestibular-Semicircular canal system The three semicircular canals arise from the utricle and have a pearshaped. The enclose the sensory cells which are stimulated by angular acceleration. They consist of the crista ampullaris on which sensory hair cell are so arranged that their cilia extend to the cupula with reaches to the roof of the ampulla.

The cupula acts as a mobile partition which closes off the pars ampullaris and is relatively

impervious

to

endolymph. The structure and

function

of

the

vestibular sensory cells are shown in Figure.

Cochlear (Acoustic End Organ) The structure of the bony and membranous cochlea are shown in Figure. • 1.Scala vestibuli. 2.Scala media 3.scala tympani 4. helicotrema • 5.Vestibular membrane • 6.Basilar membrane

Organ of Corti. Functional stucture of the organ of Corti. The cilia of the sensory cells in contact with the tectorial membrane. Radil forces occur between the tectorial membrane and the basilar membrane when the latter vibrates. This exerts a shearing force on the cilia of the hair cell and distorts them .

The shearing of the cilia is the sensory stimulus for the hair cell. The mechanical stimulation is converted in the receptor organ to a neuronal stimulus. The inner hair cells form only one row whose single elements connect to afferent individual fibers.

According to spoendlin, these constitute 95% of all fiber in the acoustic nerve, wheras the outer hair cell, althought they form three rows, converge in groups onto single afferent nerve fibers and form only 5% of the fibers of the auditory nerve. These cells are believed to generate the otoacoustic emissions.

4 Physiology of the Hearing stimulus---external canal---tympatic membranous--ossicular---stapesplate--peripheral labyrinth fluids---basic membranous---cortis hair cell---signals---nerve center hearing---analysis

( 一 ) Physiology of External Ear 1. Conduct the sound wave

2. Protect the middle ear 3. Audio amplifier for 3000Hz sound because of the external canal is 2.5 cm long (3cm long) and one end of canal is closed, so this kind of the canal can resonate with the 3000Hz sound wave.(2500Hz~4000Hz)

( 二 ) Physiology of the Middle Ear 1 Conduct the sound wave: The sound wave can be conducted to the tympanic membrane (and made the TM shaked), then the ossicular chian begain to shaked, from the malleus to the incus and the stapes, last one the footplate of the stapes began to shaking the perilyph,

then when the perilyph is shaked, the basic membrane is shaked with the Cortis organ on the basilar membrane. The hair cell of the Cortis organ receives the sound signal, the process is conducted through the air ,so we call the air conduct.

Another process is called

the

conduct.

When

bone the

sound wave shake the skull bone directly, The perilyph can be shaked, so the sound wave can induce the hair cell reaction.

The air conduct and bone conduct (AC and BC)made the hair cell active at the same time, the energe transformated to biochemical energe, It is called biochemical signal, The people can feel the sound.

The enchance sound pressure. The ossicular chain is responsible for impedance adaptation between the middle ear in a air medium and the inner ear in a fluid medium . The enchancement in pressure is 1:17 due to the ratio between the surface of the tympanic membrane and the stapes footplate. 2.

The ratio due to the mechanical advantage of the incudomalleolar joint is 1:1.3. The total pressure on the stapes footplate is therefore enhanced 22 times. So we can say through the ossicular chain the sound pressure can be enhanced about 27 dB (decibel sound pressure unit)

The physical molecular movement which we perceive as sound set the tympanic membrane in motion. The frequency of the motion is the same as that of the vibrations of the air. The transimission of the sound waves from the air medium to the fluid medium of the perilyphatic, endolymphatic space, when the sound pressure will be decreased, because the sound energe only 0.1% can be translated into fluid medium.so we can say the middle ear amplitude is very important action.

3.The Eustachian tube serves to

equalize

the

pressure

between the middle ear and the nasopharynx, and the thus to equalize the pressure on each side of the tympanic membrane.

（三） The Inner Ear The main function of the cochlea is mechanical frequency analysis which depends on its hydrodynamic. Periodic movements at the stapes are converted into movements to produce a traveling wave on the basilar membrane.

Since the inner ear fluids are incompressible, a volume displacement on the stapes footplate leads to an equal volume displacement at the round window, and this produces a bulging of the round windoe membrane equal in extent to the depression of the stapes footplate. This volume displacement produced by periodic vibrations of the stapes footplate lead to a displacement of the scala media.

A wave motion is formed by this initial displacement which proceeds along the partition to the helicotrema. This is an aperiodic vibration or traveling wave. The wavelength becomes greater. The amplitude reaches a maximum at one specific point and then immediately begin to fall sharply and dies away toward the helocotrema.

The traveling wave cause a displacement between the tectorial membrane and the basilar membrane at its point of maximal amplitude so that the cilia of the hair cells are displated at this point, forming the sensory stimulus for these mechanoreceptors.

The frequency-dependent development of the maximal amplitude on the traveling wave induces a corresponding frequency-dependent localized stimulus on the basilar membrane in those sensory cells of the organ of Cortis lying at the point of maximal amplitude.

Physiology of the Balance System Balance is maintained by coordination of visual, kinesthetic and vestibular regulatory mechanism: 1. Provide information to the central nervous system about the action of linear and angular acceleratory farce.

2. Coordinate function: movement is coordinated by continuous control of the tone of the skeletal muscles. Information from the vestibular sensory receptors is coordinated

and

integrated

information from the visual system.

with

3. Function of the Otolith Organ: Linear Acceleration Measurement: Linear acceleration is the sensory stimulus for the horizontally orientated macula of the utricle and vertical macula of the saccule. Sheaving forces occur during linear acceleration which shift the otoliths from their base,

causing shearing of the hair cells and providing an adequate stimulus for the sensory cells. The resulting neuronal impulses release the maculoocular reflex producing compensatory eye movements which ensure optimal static position of the eye during linear movement.

4.Function of the semicircular canal Angular Acceleration Measurement: a positive

or a negative angular acceleration causes endolyphatic movement within the semicircular canals lying in the plane of the centrifugal force. The stimulus always affects the semicircular canal of both sides: The cupula on one side is displaced toward the utricle and on the other side in the opposite direction .

As a result, the resting activity of the semicircular canal whose cupula is deflected in an ampullopetal direction increase whereas the active decreases in the opposite canal . This rule applies only to the horizontal canal since ampullofugal deflection causes depolarization in the vertical semicircular canals.

5 ． Audiometry 1 Testing the hearing with an Audiometer: This requires a quiet room of sufficient size(6m long) since noise and a narrow room with smooth walls produce echos which falsity results. Each ear is tested separately, the better ear being tested first. The opposite ear is masked by a moist plug of cotton wool pushed into the extenal auditory meatus .

2 Tuning fork test. (AC fork with a frequency of 512 Hz is used). a Webers fork Test: The principle of this tests on binaural comparison of bone conduction. The tuning fork is placed in the center of the skull at the hairline. The patient with a conductive hearing loss(middle ear) locatizes the tone in the diseased ear, whereas the patient with a unilateral inner ear deafness localizes the sound in the healthy ear.

B Rinners Test: The principle of this test rests on comparison of air to bone conduction. If air conduction is better than bone conduction, Renners test is positive. This is the finding in normal hearing or deafness (inner ear). If bone conduction is better than air conduction, Rinners test is negative,This is found in conductive or middle ear deafness.

c Schwabachs Test: Depends on comparison of the bone conduction of the patient with that of the examiner, but is now seldom carried out since an audiogram is always obtained if inner ear deafness is suspected.

D Gelles Test The tuning fork is placed in the same position as for Webers test. The external auditory meatus is compressed by a Politzer ballon. Excess pressure in the external auditory meatus produces stiffening of the ossicular chain and this reduces both air and bone conduction. Under the influence of increased pressure, the sound of the tuning firk fade as stiffening of the ossicular chain increases. In fixation of the due to otosclerosis the loudness of the tuning fork does not change in contrast to the result in sensorineural deafness with a mobile footplate. (Gelle-positive)

2 Audiometry 1. Pure-Tone Audiometry An audiometer is an electric tone generator used to determine the hearing threshold for pure tone,i.e. tones free of harmonics within a frequency range from 125 to 12000Hz. The hearing threshold is measured for both air and bone conduction in decibel steps. The normal hearing threshold is indicated by a stright line of 0 dB.

Hearing loss is measured in decibels relative to this threshold for all frequencies and is recorded on an audiograph. The decibel(dB) is a relative value which compares one sound pressure to another. The reference point in audiometry is the human hearing threshold for 1000Hz. The sound pressure necessary to produce the subjective impression of hearing at a threshold of 1000Hz is 20υPa(2x10-4 ubar).

This is the average value for young subjects with normal hearing and the reference point for the physical or absolute measurment of the hearing threshold in decibel [sound pressure level SPL]. The relative hearing threshuld for pure tones is a simpler method for the demonstration and description of the hearing threshold. The reference point is no longer the absolute sound pressure but the just-audible threshold of hearing measure in dB[hearing level]

This allows the use of a coordinate system with a horizontal zero line. The absolute hearing threshold is curved compared to the relative hearing threshold. The reason for this is that a greater sound pressure is needed at high and low tones to produce a similar sensation of sound near the threshold than for the central part of the frequency range around 1000Hz.

A disorder of sound conduction may be ascertained by the difference between the hearing threshold for air, bone conduction, In a manner similar to the tuning fork test.

2. Impedance Audiometry 　 This technique forms pars of the function diagnosis of the sound conduction apparatus. It includes the following two methods of investigation: Tympanometry. This is the recording of the impedance or an indirect measurement of the pressure in the middle ear when the tympanic membrane is intact, by means of pressure in the external meatus. This is an indirect test of tubal function. Measurement of the stapedius reflex. The change in impedance caused by the acoustic stapedins in reflex is measured.

Technique: The external auditory meatus is closed by an airtight plug through which pass three tubes. One tube carries the test tone;the second is connected to the pressure regulator which allows positive or negative pressure

to be produced in the external auditory meatua. A microphone is connected the third tube allowing measurement of the sound pressure of the test tone reflected from the tympanic membrane as the impedance changes.

Tympanometry: Normally, there is no pressure differential between the two sides of the tympanic membrane so that the acoustic resistance of the tympanic membrane is minimal. A recording of the impedance of the tympanic membrane during a change in pressure in the external auditory meatus allows the pressure difference on the two sides of the tympanic membrane to be determined by measurement of its compliance. The grester the pressure differential, the greater is the impedance of the tympanic membrane.

A recording of the impedance at pressure form –300H2O to +300H 2 O produce a curve with a peak at zero for a normally mobile tympanic membrane. It represents the maximal flexibility ,i.e; compliance of the tympanic membrane and thus minimal impedance, The apex of this curve is lower if the tympanic membrane is stiffened by scar tissue or damped by exudated in the middle ear.

It becomes higher with increasing compliance due to a trophic scars of the pars tensa stapedius reflex:The principal of this test is that a sound stimulus greater than 70dB above threshold induces a reflex concentration of the stapedius muscle. This causes a change of impedance at the tympanic membrane which can be recorded graphically.

The effect is absent in immobility of the tympanic membrane, in disruption of the ossicular chain and in fixation of the stapes in the oval window by otosclerosis. In simulated deafness this reflex is activated by loudness approaching the norm. In this case stimulation can be assumed.

The stapedins reflex is an acousticofacial reflex. The afferent limb is the auditory nerve and parts of the central auditory pathway up to the auditory central auditory centers. The efferent limb is formed by the connections between the auditory center and the facial nuclens, and final by the facial nerve. Measurement of the stapedius reflex is therefore very useful in topical diagnisis of a facial paralysis.

Testing of the threshold of the stapedius reflex is of considerable diagnostic importance assessment of the following disorders of hearing: otosclersis, recruitment, retrocochlour deafness, and brain stem lesions. The stapedius reflex is absent in:

(1)Retrocochlear seneorineural deafness as a result of auditory fatigue,i.e, in acoustic neuroma. (2)Otosclerosis and other middle ear disease (3)Facial nerve damage proximal to the point at which the stapedius is given off (4)Brainstem lesions with damage to the central reflex arc.

3.Electric Response Audiometry <1>Principal: The subject is exposed to an acoustic stimulus repeatedly, either regularly or irregularly, and an electroencephalogram (EEG) is used to assess whether there is any chang in brain activity. The individual response is concealed on the EEG by the noise of brain activity. However, the specific response can be distinguished from the nonspecific brain activity on the EEG by mathematical analysis of numerous evoked individual potential.

In contrast to the customary audiometric methods which test the hearing process as a complex phenomenon （ an acoustic response analyzed by the central nervous system ） . ERA provides information which cannot be obtain in any other way about the physiologic processes in the end organ. The first neuron, and within the central auditory system. The auditory evoked potentials (AEP) that can be recorded by ERA include the following:

1.Slow cortical potential (less than 50ms). This is a cortically evoked potential by means of which a complete pure-tone threshold audiogram may be recorded.

2. Late cortical potential (contigent

negtive variation) .This is an expression of generalized higher-order cortical function. 3. Middle neurogenic potentials(fast cortical potentials of 12 to 50ms). These central vertex pontential correspond principally to the auditory tract system, including the primary cortical projection.

4.Fast brain stem potentials (a) Brain stem auditory responses (ABR) (2to12ms). These are important for the recognition of retrocochlear hearing disorders The most important for diagnostic, particularly those between potential peaks Ιand ν which are prolonged both relative to the hearing threashold and absolutely in neural function disorders. (b) Frequency-following responses(5 to 15ms). The diagnosis significance of these response has not yet been established.

5. Electrocochleogram(0 to 5 ms). This method is a particular type of ERA and provides the most reliable information about the presence of a function disorder of the auditory nerve or the lower part of the brain stem. It is more effective than ABR audiometry in the assessment of inner ear and auditory nerve function. The two most usefull diagnostic parameters are the cochlear microphonics (CM) and the action potential of the auditory nerve(PI).

Measurement of the evoked brain stem potential (ABR) and cochleography are now two of the most important diagnostic methods for accurate diffentiation of cochlear from retrocochlear deafness. The latter is due to an acoustic neuroma or a tumor of

the posterior cranial

fossa or multiple slerosis. Furthermore, ERA is very useful for investigating deafness in infants and yong children.

It also serve for the assessment of residual function of the central nervous system in patients with severe head injuries, coma or other conditions marked by complete loss of consciousness. It does not, howerer, replace pure-tone

audimetry

or

tympanometry

(including the stapedius reflex).

6. Otoaoustic emission (OES) OES are sound signals emitted from the inner ear in response to acoustic stimulation. Although clinical value of spontaneous otoaoustic emission and their role in tinnitus are still debated, the recording of click-evoked OEs has become a routine diagnostic study. Clickevoked OEs cannot be recorded in ears with cochlear midfrequency hearing losses above 25 dB, but the use of sine tones as stimuli or distortion products (DP)provides reliable, reproducible frequency-specific results. DPs are intimately linked to outer hair cell function.

Evoked OEs and DPs can be used to detect early discrete lesions of the outer hair cell, and they provide an important noninvasive screening method for cochlear impairment that can even be used in newborns.

　

The rupture of the hydropic labyrinth and the resulting mixing of the potassium-rich endolymph with perilymph which is normally low in potassium leads to a considerable rise of the potassium content in the intercellular space of the perilymphatic network in which the afferent neurons of the acoustic and vestibular nerve run. These are paralyzed by depolarization due to the increase of potassium, thus causing the symptoms of cochlear vestibular failure.