ANATOMY OF THE EAR

 

1.     Clinical anatomy, physiology of the external ear

2.     Otologyc examination

3.     Clinical anatomy, physiology and examination of the vestibular system

The ear consists of three parts—the external, the mid­dle and the internal

–    External Ear

 

 

 

 

Fig. i. Anatomy of the External, Middle and Internal Ear (Semi-Schematic  View)

(1) Pinna; (2) external auditory meatus; (3) tympanic membrane; (4) tympanic

cavity; (5) malleus; (6) incus; (7) stapes; (8) Eustachian tube; (9) vestibule; (10)

semicircular canals;  (11) cochlea;  (12) auditory (acoustic) nerve

 

The shell-shaped pinna (Fig. 2) is composed of a skin-covered cartilaginous lamella whose posterior surface is evenly convex and smooth, while its anterior surface is concave, with semilunar folds and hollows between them. The skin on the anterior surface of the pinna adheres direct­ly to the perichondrium; on the posterior surface, however, it may form folds owing to the presence of a small layer of loose cellular tissue. The free anteroexternal margin of the pinna is known as the helix; towards the bottom the pinna gradually turns into the lobe devoid of cartilage and consisting of well-developed fat and cellular tissue with a small number of vessels and nerves. The small protube­rance of cartilage projecting over the external auditory mea­tus is named the tragus. In front of the helix and parallel to it is a ridge known as the an thelix, with the antitragus at its posterior end.

      

The external auditory meatus extends from the funnel-shaped hollow {cavum conchae) on the outer surface of the pinna to the tympanic membrane or drum. It is a canal directed horizontally inwards and a little forward. Its ave­rage length from the tragus top to the drum edge is 3.5 cm. The drum at the end of the canal separates the external and the middle ears. The outer third of the auditory canal consists of cartilage and membranous tissue, and both in­ner portions of bone.

The external auditory meatus is curved in the horizon­tal and  frontal  planes. The   cartilaginous and bony рог– tions of the meatus form an obtuse angle opening forward and downwards. Therefore, when examining the drum, the pinna must be pulled backwards and upwards, in order to straighten out the meatus. The oval lumen of the exter­nal auditory meatus has a longitudinal diameter of 1 cm. Its width varies with age and in different individuals. Its narrowest part is the isthmus, where the cartilaginous and bony portions form a junction and where foreign bodies are most likely to lodge. The walls of the auditory meatus are lined with skin which in the bony portion gradually be­comes thinner, loses its subcutaneous tissue and accretes closely with the periosteum. The skin covering the cartilag­inous portion abounds in hair, sebaceous glands and cerum-inous glands which secrete the earwax, or cerumen. The skin of the bony portion has neither hair, nor glands. The external bony meatus has four walls: the superior wall formed by the squamous portion of the temporal bone, its internal part bordering on the floor of the middle cranial fossa; the posterior wall serving as the front wall of the mastoid process; the anterior and inferior walls whose in­ner parts are formed by the tympanic portion of the tempo­ral bone. The external third of the anteroinferior wall is made up of cartilage with two vertical fissures through which an inflammatory process in the external auditory meatus can spread to the connective tissue surrounding the parotid gland, and vice versa. The anterior wall ad­joins the articular head of the mandible, which explains why it is painful to open the mouth and chew in cases of inflammation of the anterior wall of the external auditory meatus. Injury to the lower jaw, a fall, or an upward blow to the chin may cause a fracture in the anterior wall of the auditory meatus with the articular head of the mandible pushed backwards and upwards.

In the newborn, there is neither bony auditory mea­tus, nor mastoid process, and in place of the former there is a bony ring or annulus, which is deficient in a small upper section, and is directly connected with the membra-nocartilaginous auditory meatus. The inner border of the annulus has a bony furrow (sulcus) into which the tym­panic membrane is inserted. In the bone-free upper part, the drum is directly attached to the lower edge of the squamosa, the so-called notch of Rivinus. By the end of the third year the  external  auditory  meatus is fully  developed.

The external ear is supplied with blood by branches of the external carotid artery. It is innervated, in addition to the trigeminal branches, by the auricular nerve (ramus auricularis n. vagi) ramified in the posterior wall of the auditory meatus. Mechanical irritation of the latter wall, as in wax removal, often causes reflex cough. The lymph from the walls of the auditory meatus drains into the near­est lymph nodes located in front of the auricle, on the mastoid process, and under the inferior wall of the audi­tory meatus. Inflammations in the external auditory mea­tus are often accompanied by swelling and pain in these lymph nodes.

Tympanic Membrane

The tympanic membrane (Fig. 3, coloured Table I, Fig. 1) or drum is a thin semi-transparent elliptical disc situated between the external and middle ear. It is 9.5-10 mmX X 8.5-9 mm in size. The greater part of the drum fitted into the bony furrow of the tympanic ring is taut, and is called the pars tensa; the other,  smaller part of the drum

facing forward and upwards and directly attached to the incisure in the squamosa known as the notch of Rivinus (incisura Rivini) is lax, and is called the pars flaccida or Shrapnell’s membrane. The drum consists of three layers: an outer or epidermal layer continuous with that of the auditory meatus, a middle layer of radiating and circular connective tissue fibres, and an inner layer of mucosa con­tinuous with the mucous membrane of the tympanic cavity. Shrapnell’s membrane or pars flaccida consists only of two layers and lacks the middle stratum of fibrous tissue.

In early childhood, the drum is comparatively thick owing to the presence of a loose submucous layer. It grows compact with time and in old age becomes quite thin.

The drum is placed obliquely and not perpendicularly to the long axis of the auditory meatus, so that it faces forward, downwards and inwards. In the newborns and breast-fed babies, the drum is almost horizontal.

Examination of the drum through the auditory meatus reveals a funnel-shaped concavity in its centre with an eminence called the umbo in its deepest place. The handle of the malleus embedded in the fibrous layer of the drum starts from the umbo and goes forward and upwards to end above in a tiny knob the size of a pin-head—the short pro­cess. The two folds stretching anteriorly and posteriorly from the short process separate the upper lax membrana flaccida from the lower taut membrana tensa.

 

Middle Ear

The middle ear comprises the tympanic cavity, the mas­toid process with its cellular system and the Eustachian tube (Fig. 4), all directly interconnected.

The tympanic cavity is a small chamber, about 1 cu cm !n size, lying in the depth of the temporal bone, between the tympanic membrane and the internal ear. In front, through the Eustachian tube, the tympanic cavity communi­cates with the nasopharynx; behind, through the entrance }nto the mastoid antrum (aditus ad antrum.

Fig. 4. Section Showing Middle Ear 1) Eustachian tube; (2) tympanic cavity; (3) antrum; (4) mastoid cells

The tympanic cavity, similar to the cells of the mastoid process, contains air coming through the Eusta­chian tube.

It is customary to divide the tympanic cavity into three parts: the middle and biggest part, mesotympanum, corres­ponding to the pars tensa of the drum; the upper part, epitympanum, lying above the former and also known as the epitympanic recess or attic; the lower part, hypotym-panum, lying below the drum level.

The tympanic cavity has six walls.

The roof of the tympanic cavity is a thin plate of bone separating the tympanic cavity from the middle cranial fossa where the temporal lobe is situated. This plate often has congenital fissures through which vessels pass from the middle cranial fossa. These anatomical features may ac­count for the meningeal symptoms frequently observed in young children with acute otitis media.

The inferior wall or floor of the tympanic cavity is se­parated from the jugular bulb by a fairly thick bony plate. Bone fissures in this wall are rarely found.

The Eustachian tube begins with an opening in the an­terior wall separating the tympanic cavity from the inter­nal  carotid  canal.

An opening in the upper part of the posterior wall leads to  the  mastoid  antrum   (aditus ad antrum mastoideum).

The internal wall separates the tympanic cavity from the internal ear. It is marked by a gentle eminence, the *
promontory   (promontorium),  corresponding to  the  basalturn  of the cochlea.  Above  and  behind  the  promontoryis an oval window or the fenestra vestibuli which leadsinto the vestibule and is closed by the foot plate of the stapes.  Behind  and below the promontory in a niche is a round window or the fenestra cochlea which leads intothe cochlea, and is filled with a thin membrane, the secon­ dary ympanic membrane.                                                           ‘

 

 

On the internal wall above the oval window is a bony torus—the horizontal part of the facial nerve canal. On reaching the entrance to the antrum, the facial nerve ca­nal turns downwards to form a descending knee, then passes behind the posterior wall of the auditory meatus and through the stylomastoid foramen to the base of the skull. The walls of this bony canal may be eroded; in such cases, the middle ear mucosa may come through fissures into direct contact with the sheath of the facial nerve. This sometimes causes the development of facial paresis and paralysis in suppurative otitis media. Some­what behind and above the facial nerve canal, on the inner wall of the aditus ad antrum, lies the peak of the horizon­tal semicircular canal the clear contour of which serves for orientation in operations on the middle ear.

 

The external wall of the tympanic cavity is formed by the tympanic membrane, and above the drum—by the ex­ternal bony wall of the epitympanic recess or attic.

The tympanic cavity contains the three auditory ossi­cles—the malleus, the incus and the stapes (Fig. 5)—which are interconnected by joints and ligaments to form a con­tinuous and rather flexible chain between the drum and the oval window. The handle of the malleus is woven, as it were, into the fibrous layer of the tympanic membrane, and the foot plate of the stapes is fixed in the oval window by means of an annular ligament. The incus lies between the malleus and the stapes. The whole system is kept in place by ligaments fastening the malleus and incus to the walls of the tympanic cavity.

The tympanic muscles. There are two muscles in the tympanic cavity: (1) The tensor tympani muscle which stretches the tympanic membrane. It lies in the bony ca­nal above the Eustachian tube, and is attached to the handle of the malleus. (2) The stapedius muscle which arises from the posterior wall of the tympanic cavity and is attached to the head of the stapes by a slender tendon. The tensor tympani is innervated by a branch of the trigem­inal nerve, and the stapedius muscle by a branch of the facial nerve.

The Eustachian or auditory tube which is about 3.5 cm in length connects the tympanic cavity with the nasopha­rynx. The upper third of this tube, adjoining the tympa­nic cavity, has bony walls, while the remaining lower por­tion leading into the nasopharynx is made up of membrane and cartilage. The movement of the cilia of the ciliated epithelium lining the Eustachian tube is towards the naso­pharynx. At rest, the Eustachian tube is in a collapsed state, but with each swallowing movement it opens by contrac­tion of the soft palatal muscles attached to it, to let air into the tympanic cavity.

The mastoid process located just behind the external au­ditory meatus is a bony structure protruding downwards with the sternocleidomastoid muscle attached to it. In young children, the mastoid process is not fully developed and represents a bony tubercle behind the osseous tym­panic ring.

The upper border of the process is the temporal line (linea temporalis), a bony torus which is a backward ex­tension of the zygomatic process. The floor of the middle cranial fossa usually lies on a level with this line.

The anterior wall of the mastoid process is the posterior bony wall of the external auditory meatus. Behind the spot where the superior wall of the auditory meatus mer­ges with the posterior wall, there is a small bony peak or the suprameatal spine (spina supra meatum) lying above the external auditory meatus. Behind the spine there is a smooth depression, the mastoid fossa (fossa mastoidea). The suprameatal spine and the temporal line are impor­tant landmarks in surgical operations; the mastoid antrum (antrum mastoideum) lies on the projection of the mas­toid fossa (fossa mastoidea) in the depth of the mastoid process.

The internal wall of the mastoid process abuts upon the labyrinth, and more posteriorly is bordered by the post-cranial fossa. On the surface facing the post-cranial fossa there is a rather wide S-shaped groove, the sigmoid sulcus, containing part of the sigmoid sinus of the dura mater. The central part of the mastoid process is the antrum lying just behind the epitympanic recess. The antrum com­municates with the tympanic cavity and the air-filled cells of the mastoid process. The superior wall or roof of the antrum separates it from the middle cranial fossa.

The following types of structure are to be found in the mastoid process: the pneumatic or large-celled, the diploic and the compact or “sclerotic”. In the case of pneumatic structures, the cavity of the mastoid process is divided by thin bony partitions into a lattice of larger and small­er cells. The diploic structure has tiny cells resembling a diploetic bone; the most frequent is the mixed form of mastoid structure where smaller cells are to be found along­side bigger ones. In compact structures the bone is indu­rated and the cells are very few; this structure frequently occurs as a result of chronic suppurative otitis media.

-The walls of the tympanic cavity, antrum and mastoid cells are lined with a continuous thin mucosa devoid of mucous glands. The mucous membrane of the Eustachian tube  and   of  the  adjoining part of the tympanic cavity

floor is covered with ciliated columnar epithelium; the mucosa of the cartilaginous part of the Eustachian tube contains mucous glands which are absent in the mucosa of the  other parts  of the middle  ear.

The middle ear is supplied with blood mainly by branches of the external carotid artery. Venous blood drainage from the middle ear is maintained by the veins of the dura mater, the venous sinuses and the venous plexuses round the carotid artery. Lymph drainage is carried out in two ways: (1) through the lymphatic vessels of the Eustachian tube to the retropharyngeal lymph nodes and further to the deep cervical glands; (2) through the lymphatic ves­sels across the tympanic cavity to the lymphatic ducts of the external auditory meatus and the lymph nodes in front of and behind the auricle. The nerve supply of the middle ear is through branches of the glossopharyngeal, facial and sympathetic nerves.

Internal Ear or Labyrinth

The internal ear consists of membranous and bony laby­rinths, the latter surrounding the former like a capsule. The membranous labyrinth is filled with fluid known as endolymph, while around it and separating it from the bony shell is the spinal fluid known as perilymph.

The bony labyrinth is made up of the vestibule, three semicircular canals and the cochlea (Fig. 6).

The vestibule (vestibulum) lies in the centre of the bo­ny labyrinth on whose external wall is the oval window; on the opposite, internal wall, there are two recesses for the two membranous sacs of the vestibule.

The front sac known as the saccule (sacculus) commu­nicates with the membranous cochlea lying before the ves­tibule, while the rear sac or utricle (utriculus) is connect­ed with the three membranous semicircular canals pass­ing behind and above the vestibule. The intercommuni­cating sacs of the vestibule contain the statokinetic recep­tors or maculae acusticae, otolithic organs made up of a highly-differentiated specific neuroepithelium covered with a membrane containing granules of carbonate and phos­phorate of lime, i.e. the otoliths.

 

 

Fig. 6. Bony Labyrinth on Right Side

(1; frontal semicircular canal; (?) ampulla of frontal semicircular canal; (3) apex of cochlea; (4) medial turn of cochlea; (5) apical turn of cochlea; (6) basal turn of cochlea; (7) round window; (8) oval window; (9) ampulla of sagittal se­micircular canal; (10) sagittal semicircular canal; (11), (12) crura; (13) ampulla of horizontal semicircular canal; crus commune of frontal and sagittal semicir­cular canals

The semicircular canals are set at right angles to each other and represent the three planes of space. They are three iumber: the external or horizontal, the superior or frontal, and the posterior or sagittal. One end of each canal opens out into a larger space known as ampulla, the other end is even. The frontal and sagittal canals have a common even stem  (crus commune).

The jynpulla of each membranous canal contains a ridge. the crista ampullaris, which is a receptor, i.e. a nerve ending consisting ot a highly-differentiated neuroepithelium or hair and supporting cells.

The free surface of the hair cells is covered with hairs which respond to the slightest displacement or pressure of the endolymph.

The receptors of the vestibule and semicircular canals are the peripheral nerve endings of the vestibular analysor.

 

Fig. 7. Organ of Corti  (Schematic View)

(1) basilar membrane: (2) tectorial membrane; (3), (4) hair cells; (5) supporting cells;  (6) nerve   fibres reaching hair cells

cate at the apex of the cochlea through a small opening known as the helicotrema   Both channels are filled with perilymph. ”

The  scala  vestibuli  communicates  with  the  vestibule, j while the scala tympani borders on the tympanic cavity < through the round window covered by the secondary tym­panic membrane.

The scala vestibuli of the cochlea contains the thin Rei sner’s  membrane which extends  from  the  osseous  spirn lamina to cut off a small membranous canal of trianguli> section filled with endolymph and known as the cochles duct or ductus cochlearis.

The organ of Corti  (Fig. 7.), a complex receptive stru ture of the auditory analyzor, rests on the basilar membrai (membrana basilaris), the lower wall of the ductus cochleii ris.  The  basilar membrane  is  an  arrangement  of elastu fibres of different lengths strung from the edge of the bony spiral lamina to the opposite, outer wall of the cochlea.

The organ of Corti has a very complex histological struc­ture containing hair cells and supporting cells. The sen­sory cells covered with hairs are situated in small groups between the supporting cells. The cells are covered with a membrane called the tectorial membrane (membrana tec-toria). The sensory hair cells are surrounded by a network of cochlear nerve branches leading to the spiral ganglion of the auditory nerve in the bony spiral lamina and fur­ther by intricate routes to the brain cortex.

Video Video

 

PHYSIOLOGY OF THE ЕAR

The ear is one of the sense organs by which man com­municates with the outer world.

I.P. Pavlov’s theory of the sense organs presents them as analyzors, each making up a single system of the fol­lowing components: (1) the peripheral part or receptors, i.e. nerve endings adapted to respond to certain types of stimulation; (2) nerve conductors to convey the impulse from the receptor; (3) a central department in the brain cortex for a thorough analysis of all stimuli and their trans­formation  into sensations.

 VIDEO  VIDEO  VIDEO

 

Auditory Function

The auditory function of the ear consists in the conduc­tion of sounds through the external and middle ears.or cranial bones”and their reception by the spiral organ of Corti, the receptor of the auditory analyzor. The external and middle ears make up the sound-conducting apparatus, whereas the internal ear, specifically, the organ of Corti, belongs to the sound-perceiving apparatus.

The auricle in man is of lesser importance than in ani­mals, and yet there is no doubt that it plays a certain role in collecting sounds and  determining their direction.

The external auditory meatus conducts sound waves from the outer medium to the tympanic membrane. The mea-tal diameter has nothing to do with hearing acuity. Its atresia, however, as well as its complete obstruction, as occurs in earwax impaction, hinders the passage of sound waves and considerably impairs the hearing.

Sound  waves  striking  the  tympanic   membrane  set  it to vibration. The drum being onnected to the handleof the malleus, these vibrations are transmitted to the os­sicular chain; and the foot plate of the stapes, closing the oval window of the labyrinth, rocks in and out of the oval window according to the phase of sound vibrations. The vibration of the foot plate of the stapes in the oval win­dow sets up vibrations in the perilymph. These vibrations are transmitted to the basilar membrane and the organ of Corti which it supports.

The vibration of the basilar membrane causes the hair cells of the spiral organ of Corti to get in touch with the overhanging tectorial membrane. At the same time, the mechanical energy of vibrations changes into the physio­logical process of nervous excitation which is conveyed to the most delicate receptors of the auditory nerve to be passed further to its nuclei in the medulla oblongata and through appropriate canals to the cortical auditory centres in the temporal brain lobes where nervous impulses are interpreted as sounds heard.

The internal ear performs the most important functions of the ear, because it is here that sound perception takes place.

Normal hearing depends on the normal condition of the apparatus for sound perception and conduction.

The tension of the drum and the ossicular chaieces­sary for normal sound conduction is maintained by the combined action of the tympanic muscles. For normal vib­ration the tympanic membrane requires a constant equi­librium between air pressure in the middle ear cavity and in the outer air, that is on both sides of the drum. This is maintained by the passage of air through the Eustachian tube during swallowing. Disturbance of air supply to the middle ear through the Eustachian tube causes air in the middle ear to be sucked in and the drum to be indrawn, which is followed by deterioration of hearing. The normal condition of the sound-conducting apparatus is extremely important for the transmission of low tones to the labyrinth, that is, sounds with a low frequency of vibrations per se­cond.

There are two ways of conducting sound waves to the labyrinth: air conduction (through the external auditory meatus, the tympanic membrane and the chain of ossicles) and bone conduction (directly through the cranial bones and the stapes).

High tones, i.e. sounds of a high vibration frequency per second, are easily conducted to the labyrinth not only through the tympanic membrane and the ossicular chain, but through the cranial bones and the stapes as well.

Man can hear external sounds with a frequency of 16 to 20,000 cycles per second,,

The human ear can differentiate between sounds of differ­ent pitch, intensity and timbre. There are a number of theories which seek to explain the essence of hearing and the ability of the ear to differentiate between sounds. The oldest and most widespread among them is the resonance theory advanced by Helmholtz in 1863 and based on the physical phenomenon of sympathetic vibration. According to this theory the fibres of the basilar membrane vibrate in unison with sounds, similar to the action of strings in certain musical instruments, such as the piano or the harp. The short, thin and tighter fibres of the basilar membrane which lie in the basal turn of the cochlea vibrate in unison, i.e. resonate when stimulated by a high tone, whereas the longer, thicker and less taut fibres in the apical turn of the cochlea resonate in response to low tones.

There are a number of serious objections to the resonance theory as it oversimplifies the essence of hearing as a physiological process by describing it from the mechanical aspect alone, and fails to give a picture of the physiolo­gical properties of the auditory analyzor as a whole. It should be noted, however, that the localization of percep­tion of high and low tones in the basal and apical cochlear turns respectively, on which the resonance theory is based, has been confirmed by experiments and clinical observa­tions.

In opposition to the resonance theory so-called telepho­nic theory of hearing asserts that the basilar membrane vibrates all over like a telephone membrane. It denies any analysis of sound being made in the peripheral receptor contained in the cochlea. This concept has been disproved by clinical practice and experimental research.

The first to prove beyond doubt that sounds of different pitch are perceived in different parts of the cochlea wasL.A. Andreyev by experiments with conditioned reflexes made in I.P. Pavlov’s laboratory. The experiments were made on dogs which developed conditioned reflexes of sali­vation to tones of low, moderate and high frequency. After the reflex had been firmly established, the cochlea on one side was completely destroyed, and the animal retained its conditioned reflex. This was followed by a selective destruction of different parts of the cochlea.

Destruction of the cochlear apex with a thin drill caused disappearance of the conditioned reflex to low-pitched sounds, whereas destruction of the cochlear base was fol­lowed by disappearance of the reflex to high-pitched sounds. These experiments have proved that an injury to the api­cal turn of the cochlea causes loss of low tone perception, whereas an injury to the basal turn of the cochlea is accom­panied by loss of high tone perception.

Thus, according to the teachings of I.P. Pavlov and his followers, the peripheral receptor of the auditory analyzor makes a primary analysis of sound by converting the lat­ter’s mechanical energy into the physiological process of nervous excitation. This, in turn, is conveyed through nerve canals to appropriate centres in the brain cortex where the nerve impulses are finally interpreted as sounds heard. I.P. Pavlov’s teaching gives a clear idea of the functions of each part of the auditory analysor, thus presenting the latter’s entire activity as a single physiological process.

The faculty of locating the origin of sounds, the so-called ototopia depends upon binaural hearing. It is largely lost in people with unilateral hearing, who have to turn their heads in various directions to locate the origin of sound. People with two healthy ears can easily determine the direction of sounds without turning their heads.

The ability to find the direction of sounds is a function of the central nervous system. If a sound comes from one side, it arrives at the ear on the other side with an insigni­ficant delay of 0.0006 sec.

This delay makes it possible to ‘determine the direc­tion of sound.

Orientation of the body and its individual parts in space is made possible by co-operation of many receptors. Apart from eye-sight, the location of the body and its parts is identified through nerve endings lying in the skin, as well as in the muscles, joints and tendons, which are called proprioceptors.

In addition to the above-mentioned receptors, the cere­bellum and, above all, the vestibular apparatus perform an important function in body orientation and in main­taining equilibrium at rest and in motion. The vestibular apparatus consists of the vestibule containing the otolith system and the semicircular canals with their ampullae containing the nerve endings of the vestibular analysor.

The accelerations imparted to the body during its move­ment in space are adequate or specific stimulants for the nerve endings of the vestibular analyzor. Movements along a straight line cause displacement of the otoliths and sti­mulate the receptors of the otolith, or statolith, structure contained in the vestibular sacs. Angular or rotatory mo­tions are followed by displacement of the endolymph in the semicircular canals and stimulation of receptors in the am­pullae.

 

Stimulation of the receptors of the vestibular analyzor produces a number of reflex reactions which cause a change in the tonus of some muscle bundles of the torso, extre­mities, neck and eyes. This, in turn, causes the whole body to change position and maintain balance.

One of the unconditioned reflexes observed in stimula­tion of the semicircular canals is nystagmus which con­sists in a rhythmic movement of the eyes in a certain di­rection and back, such as lateral and vertical nystagmus. Nystagmus may be observed in different positions of the eyeball, for example, in gazing straight ahead and in an extremely side-long glance. The observation of nystagmus !S used to assess the reaction of a stimulated vestibular apparatus.

The role of the vestibular apparatus becomes particular­ly apparent during an acute disturbance or cessation of *ts function, which occurs in some diseases. The patients suffer from severe static and dy­namic disorders: they are un­able to stand, walk and sit; they cannot co-ordinate their move­ments, develop spontaneous nys­tagmus, etc. This is accompa­nied by vertigo, nausea and vo­miting. Three to four weeks la­ter these symptoms subside due to compensation from the cent­ral systems. A more or less in­tensive reaction of the vestibular apparatus to adequate, i.e. spe­cific, stimulation depends on the state of the central ner­vous system, its higher divi­sion, the brain cortex, in parti­cular.

This examination begins with collection of  data on the case, followed   by   inspection   of the ear and a functional   examina­tion of  hearing.   In  a  complex  examination nose and throat,   the   latter  two are always be dealt with.

A case history must include an account of the symp­toms as described by the patient, and the circumstances under which the illness began.

In gathering this information attention should be paid to (a) ear pain and its character; (b) pus discharge; (c) deterioration of hearing or total deafness; (d) tinnitus; (e) dizziness. It is equally important to find out whether the patient complains of headaches, chills, etc. Among the nu­merous causes of ear diseases the most frequent are inflam­mations in the nose and throat which produce acute otitis media. Therefore, it is important to know if the ear disease in question was preceded by influenza, acute rhinitis, etc. Then general details should be obtained, i.e. information about the general state of health, past diseases, infectious ones in particular, working and housing conditions, and other facts relating to the everyday life of the patient. Examination of the ear includes an external examination and palpation of the ear and the mastoid process, as well as inspection of the external auditory meatus and the tym­panic membrane (otoscopy).

 

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Otoscopy

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Examination of the external auditory meatus and the tympanic membrane, as well as the tympanic cavity when the drum is absent, requires artificial lighting and a head mirror (Fig. 9) to reflect the light into the ear and the ear speculum (Fig. 10). The best source of illumination is a 50 to 60 W frosted bulb; the head mirror is a round slight­ly concave mirror 8 to 9 cm in diameter with the focal length of 20 cm and a hole in the middle. In the absence of electric lighting, any source of illumination including daylight should be used. The examination is made in a sitting posture with the light placed on a level with the patient’s

head, to the right and a little behind, as shown in Fig. 8. The head mirror is so fixed before the examiner’s left eye that the eye, the mirror hole and the ear under examina­tion are in one straight line.

       

Both eyes are used when making an otoscopic examina­tion, the left eye necessarily peering through the mirror hole. Before inserting the ear speculum, one should exa­mine the meatal opening and measure its diameter. Little children are examined with the aid of an assistant who keeps the child’s head firmly pressed to his breast with one hand, and holds its arms with the other. The legs of the child are pressed between the legs of the assistant.

The ear speculum with its dilated part held between the thumb and the forefinger is carefully introduced into the meatal opening with a gentle rotation to a depth of 1 to 1.25 cm without touching the bony part, in so far as is practicable. At the same time, the pinna is pulled up­wards and backwards in adults and downwards and back­wards in small children to straighten out the angle of the meatus. Where there are swellings, fissures or eczema, the speculum should be introduced with particular caution to avoid pain. Lightly moving or tilting the inner part of the speculum, the examiner inspects in turn the internal parts of the auditory meatus and the entire surface of the drum. In examining the meatal canal major attention should be given to the posterosuperior wall to detect possible thickenings and even considerable overhangings extending downwards and outwards.

It is possible to examine the ear without the aid of arti­ficial lighting only in cases of a sufficiently wide and fairly straight auditory meatus. To avoid obstructing the light with his own head, the doctor should be at some distance from the patient, although ear details will not be seen so clearly.

The normal drum is an oval disc of a pearly grey colour on which the following landmarks are clearly visible (Fig. 3, coloured Table I, Fig. 1). A whitish-yellow knob, the size of a pin-head, projecting from the anterosuperior part of the drum is the short process of the malleus. Two grey-isk-white streaks extending backwards and forwards from it are the anterior and posterior folds separating the anterosuperior part of the drum, the pars flaccida of Shrap-nell, from the lower tense part, the pars tensa. From the short process the handle of the malleus can be seen extending downwards and backwards. Its broader lower end termi­nates at the centre of the drum, the umbo. At otoscopy, the light rays from the mirror form on the drum a brilliant cone-shaped light reflex with the top pointed to the centre (umbo) and the base facing the anteroinferior edge of the tympanic   membrane.

For convenience, in describing changes on the tympanic membrane, the-latter is divided into four quadrants (Fig. 3) by an imaginary line extending the malleus handle to the edge of the drum and by an intersecting line drawn at right angles to the first through the centre of the umbo; thus forming the anterosuperior, anteroinferior, postero­superior and posteroinferior quadrants. The drum is very closely connected with the tympanic cavity; therefore, it will reflect any existing morbid condition of the middle ^ear. Thus, a change in colour, for instance, redness of the drum, indicates otitis media. Changes in location of the landmarks, the light cone in particular, manifest them­selves in cases of drum retraction resulting from chronic diseases  of  the  middle  ear.

The mobility of the drum may be tested by the use of ^a pneumatic speculum (Fig.  11). The dilated end of this speculum is hermetically sealed with a lens, and a tube branching from its side is attached to a rubber bulb. To facilitate observance of drum mobility through the lens, the speculum is tightly fitted into the auditory meatus, the air being alternately compressed and rarefied with the rubber bulb, causing the drum to move in and out. At otoscopy the examination begins with the healthy ear in order to compare it with its diseased counterpart.

Examination   of the Auditory   Function

The functional examination of hearing is made by means of whisper and conversation voice, tuning forks and audio­meters. The whisper test should be carried out in a quiet room of adequate size. Each ear is examined separately, while the other ear is closed with a finger tip. The patient turns the ear to be tested to the examiner so that he does not see the letter’s face and cannot guess his words by watch- ing the lip movements. The whisper should always be of the same intensity obtained by breathing out effortles­sly and using the residual air to call out words.

The normal ear can hear whispered speech with a preva­lence of low tones, i.e. consonants, labial and palatal sounds, b, p, t, m, n, at a distance of 5 to 10 m; whispered speech with a prevalence of high tones, i.e. sibilants, s, ^z) ch, sh, shch, is heard at a distance of up to 20m. Esti­mation of hearing by the whisper test may be made by calling out numbers from one to a hundred and selecting numbers with low sounds, such as two, five, nine, and with ^Qigh sounds, such as six, seven, sixty-six, etc. As the fig­ures uttered can be easily guessed by some patients, the hearing test should rather be made with specially selected words of high and low tones. A table of such words has

been compiled by V.I. Voyachek. The first group of words primarily contains low sounds heard at a distance of 5 m on the average; the second group is mainly composed of high sounds heard at a distance of 20 m. The following is a conjectural selection of English words based on the same principle.

By using this table one may roughly determine the na­ture of the ear disease. A poor perception of words of the first group (low tones) will indicate a defect in the sound-conducting apparatus, i.e. conduction deafness. Impaired hearing of words from the second group (high tones) will point to a lesion in the sound-perceiving apparatus, i.e. nerve deafness. If whispered speech is heard at a di- stance of 6 to 8 m, the hearing is practically normal. If the patient does not hear the whispered speech at all, con­versation voice or forced voice tests should be used. In examining unilateral deafness it is not enough to close the normal ear with a finger tip to shut out all sound. Therefore, a special noise-box (Fig. 12) is put into the normal  ear to  exclude  its hearing altogether.

Other methods of excluding the normal ear, such as rub­bing the pinna with the flat of the open hand or shaking the  finger plugging the auditory canal are less reliable.

Tuning fork tests. Hearing acuity is determined by the whis­per test with comparative ease and quickness. But the differential diagnosis between the conduction and percep­tion types of deafness, as well as a more accurate determi­nation of hearing acuity is made by using tuning forks (Fig. 13). The tuning fork produces a clear tone without overtones. The human ear can hear in a sound range of 16 to 20,000 cycles per sec. The highest and lowest tones perceptible to the human ear indicate the higher and low­er limits of hearing respectively. The tones heard between the upper and lower limits of hearing make up the so-called audible range or register. This range decreases noti­ceably with age, mostly due to reduction of the upper limit of hearing. A set of tuning forks can be used to exa­mine hearing acuity for different tones, from 64 to 4,096 cycles per sec, as well as to determine air and bone con­duction. To estimate air conduction, a sounding tuning fork is held near the meatal opening. When bone conduc­tion is being determined, a sounding tuning fork is placed on the head or the mastoid process. Iormal hearing air conduction is better than bone conduction. In medical practice, bone and air conduction is examined only with two tuning forks, of the types C₁₂₈ and C’_2i048. The following experiments can help in a differential diagnosis between the  conduction   and  perception  types  of  deafness.

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The Weber test of sound lateralisation (Fig. 14a). A C₁₂₈ tuning fork is” sounded and placed on the vertex, and the patient is asked to say in which ear the sound is heard best. In case of conduction deafness, such as caused by earwax impaction in the auditory meatus or otitis media, the sound will be best heard in the diseased ear. In the event

of nerve deafness, the tuning fork will be best heard in the normal   ear.

^” The Rinne tesi or comparison between bone and air conduction (Fig. 14b). When_a sounding C_3La8JLuning_jfork applied to the mastoid process” cao longer beTTeanT, it~is~hil(rto the_ear; it then appears Jhat_the_soiind is heard longer byair Conduction than by ~bone~conduction. nor­mally for &1) to 90 sec compared~”to 45 sec in the casejii Bone conduction. In such circumstances^—the~^lnnltest is considered positive (Rinne+); a positive Rinne is ob­served in patients with normal hearing, as well as in those with nerve deafness, jn conduction deafness the jiutalion of bone_conduction_inay_^e_gaual to thatof air conduction or~even~exceed~it^considerablY, in Iwhich_”caseTEiIIBinna test~Ts~coBsidered Taegative   (Rinne —).

 

 The Schwabach test compares the duration of bone con­duction from the vertex or the mastoid process of the pa­tient with the normal bone conduction of the examiner. In conduction deafness, bone conduction is lengthened, whereas ierve deafness it is shortened.

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The acuity of hearing for high tones is determined with a G₄ tuning fork of 2,048 cycles per sec. A certain high tone loss is noticeable in deafness due to old age and ierve deafness.

A more accurate and quicker examination of hearing is made with a special instrument called the audiometerwhich can be used to estimate hearing acuity within the entire tone range important in the estimation of hearing.

 

 

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Examination  of tho  Vestibular   Fiinrtinn

Examination of the vestibular function is preceded by questioning and examining the patient. Patients with vestibular disturbances usually complain of giddiness, unstready gait, as well as occasional sickness and vomiting. Examination of the patient may reveal a nystagmus often associated with a functional vestibular disturbance. Vesti­bular nystagmus may be observed in a patient looking sideways and sometimes in a patient staring straight ahead. Disorders in co-ordination, static equilibrium and balance of   walking  are   also likely   to   happen.   Special   clinical tests are used to examine the vestibular function. These tests are based on procedures for ar­tificial stimulation of the vesti­bular receptors to produce nys­tagmus. There are three basic tests of this kind, the rotation, caloric and compression  tests.

The rotation test involves turning the patient’s body around the vertical axis to cause endolymph movements in the semicircular canals, which sti­mulate the receptors and pro­duce nystagmus. The patient is seated in a chair (Fig. 15) which can be rotated horizontally and is revolved at a speed of 10 rev­olutions in 20 sec. This stirs up the endolymph in the semicir­cular canals. When the chair is stopped abruptly after rota­tion to the right, the patient will have leftward nystagmus; Fig. 15. Rotating Chair       if the  procedure is reversed the

 

 

 

 

 

nystagmus will be in the opposite direction. So that the nystagmus may be studied, the patient is directed to look at the examiner’s finger, which is held at a distance of 30 cm towards the side where the nystagmus is expected.

In most people with normal vestibular sensitivity the duration of post-rotational nystagmus is, on the average, 30 to 35 sec. Among the disadvantages of this test is that rotation stimulates both labyrinths, though with unequal force.

The caloric test is based on the phenomenon of endo­lymph movement in the semicircular canals under the effect  of cooling or heating by artificial means.

During this test each labyrinth is examined separately. Each ear in turn is syringed with water; a cold douche at 16° to 30 °G causes nystagmus to the side away from the ear being tested, whereas a warm douche at 38° to 41 °C causes nystagmus  in  the opposite  direction.

Absence of nystagmus in the caloric test may indicate a  loss  of  vestibular sensitivity.

In case of dry perforation one should abstain from the caloric test for fear of provoking a relapse of suppurative otitis.

Some pathological conditions of the labyrinth are likely to produce a nystagmus caused by air compression or rare­faction in the auditory canal. This is known as the com­pression test. If there is a fistula or a bone defect in a laby­rinth wall (external semicircular canal), the air compres­sed with a bulb in the auditory meatus causes nystagmus towards the diseased ear, whereas aspiration produces nystagmus to the opposite side. This phenomenon is called  the   fistular  symptom.