EAR.pptxhcufifjgufufkzjzjduzuitskufjsykfjzk

Rjzkyxkgzjxpjc

1. EAR

2. ANATOMY OF EAR EXTERNAL EAR MIDDLE EAR INTERNAL EAR

3. EXTERNAL EAR The external ear consists of: (a) The auricle or pinna (b) the external auditory meatus.

4. Auricle/Pinna The auricle is the part seen on the surface, the part the layman calls the ear. The greater part of it is made up of a single crumpled plate of elastic cartilage which is lined on both sides by skin. However, the lowest part of the auricle is soft and consists only of connective tissue covered by skin: This part is called the lobule for wearing the ear rings. The prominent rim of the auricle is called Helix Another curved prominence parallel with and in front of the helix is called antihelix The antihelix describes a curve around a deep capacious cavity – concha Small pointed eminence in front of the concha – Tragus

5. The blood supply of the auricle is derived from the posterior auricular and superficial temporal arteries. The lymphatics drain into the preauricular, postauricular and superficial cervical lymph nodes. NERVE SUPPLY The upper two-thirds of the lateral surface of the auricle are supplied by the auriculotemporal nerve The lower one-third by the great auricular nerve. The upper two-thirds of the medial surface are supplied by the lesser occipital nerve lower one-third by the great auricular nerve. The root of the auricle is supplied by the auricular branch of the vagus .

6. EXTERNAL AUDITORY MEATUS The external auditory meatus conducts sound waves from the concha to the tympanic membrane. The canal is S-shaped. Has bony and cartilaginous part. the medial two-thirds or 16mm is bony, and the lateral one-third or 8 mm is cartilaginous. The canal is oval in section. The bony part is narrower than the cartilaginous part. The narrowest point, the isthmus , lies about 5 mm from the tympanic membrane. The bony part is formed by the tympanic plate of the temporal bone and C shaped in cross section. In the posterosuperior part the wall of the meatus is formed by a part of the squamous temporal bone. The meatus is lined by thin skin. The cartilaginous part is also C-shaped in section. The lining skin is adherent to the perichondrium, and contains hairs, sebaceous glands, and ceruminous or wax glands. Ceruminous glands are modified sweat glands.

7. Blood supply: The outer part of the canal is supplied by the superficial temporal and posterior auricular arteries, and the inner part, by the deep auricular branch of the maxillary artery. Lymphatics: The lymphatics pass to preauricular, postauricular and superficial cervical lymph nodes. Nerve supply: The skin lining the anterior half of the meatus is supplied by the auriculotemporal nerve, and that lining the posterior half, by the auricular branch of the vagus .

8. TYMPANIC MEMBRANE This is a thin, translucent partition between the external acoustic meatus and the middle ear. It is oval in shape, measuring 9 x 10 mm. It is placed obliquely at an angle of 55 degrees with the floor of the meatus. It faces downwards, forwards and laterally The membrane has outer and inner surfaces. The outer surface of the membrane is lined by thin skin. It is concave. The inner surface provides attachment to the handle of the malleus which extends up to its center. The inner surface is convex. The point of maximum convexity lies at the tip of the handle of the malleus and is called the umbo.

9. The membrane is thickened at its circumference which is fixed to the tympanic sulcus of the temporal bone on the tympanic plate. Superiorly, the sulcus is deficient. Here the membrane is attached to the tympanic notch. From the ends of the notch two bands, the anterior and posterior malleolar folds are prolonged to the lateral process of the malleus. The greater part of the tympanic membrane is tightly stretched and is, therefore, called the pars tensa , The part between the two malleolar folds is loose and is called the pars flaccida . The pars flaccida is crossed internally by the chorda tympani .This part is more liable to rupture than the pars tensa . The membrane is held tense by the inward pull of the tensor tympani muscle which is inserted into the upper end of the handle of the malleus.

10. STRUCTURE Tympanic membrane is composed of 3 layers- 1.The outer cuticular layer of skin 2.The middle fibrous layer made up of superficial radiating fibres and deep circular fibres . The circular fibres are minimal at the centre and maximal at the periphery. The fibrous layer is replaced by loose areolar tissue in the pars flaccida 3. The inner mucous layer is lined by a low ciliated columnar epithelium.

11. Blood Supply 1.The outer surface is supplied by the deep auricular branch of the maxillary artery. 2.The inner surface is supplied by the anterior tympanic branch of the maxillary artery and by the posterior tympanic branch of the stylomastoid branch of the posterior auricular artery Venous Drainage - Veins from the outer surface drain into the external jugular vein. Those from the inner surface drain into the transverse sinus and into the venous plexus around the auditory tube. Lymphatic Drainage - Lymphatics pass to the preauricular and retro pharyngeal lymph nodes. Nerve Supply - 1. Outer surface: The anteroinferior part is supplied by the auriculotemporal nerve, and the posterosuperior part by the auricular branch of the vagus nerve. 2. Inner surface: This is supplied by the tympanic branch of the glossopharyngeal nerve through the tympanic plexus

12. MIDDLE EAR The middle ear is also called the tympanic cavity, tympanum. The middle ear is a narrow air filled space situated in the petrous part of the temporal bone between the external ear and the internal ear. Shape and Size The middle ear is shaped like a cube. Its lateral and medial walls are large, but the other walls are narrow Its vertical and anteroposterior diameters are both about 15 mm. When seen in coronal section the cavity of the middle ear is biconcave, as the medial and lateral walls are closest to each other in the centre . The distances separating them are 6mm near the roof, 2 mm in the centre , and 4 mm near the floor.

13. Parts The cavity of the middle ear can be subdivided into the tympanic cavity proper which is opposite the tympanic membrane; and the epitympanic recess which lies above the level of the tympanic membrane. Communications The middle ear communicates anteriorly with the nasopharynx through the auditory tube, posteriorly with the mastoid antrum and mastoid air cells through the aditus to the mastoid antrum.

14. Contents The middle ear contains the following: 1.Three small bones or ossicles namely the malleus, the incus and the stapes. The upper half of the malleus, and the greater part of the incus lie in the epitympanic recess. 2.Ligaments of the ear ossicles. 3.Two muscles, the tensor tympani and the stapedius. 4.Vessels supplying and draining the middle ear. 5. Nerves: Chorda tympani and tympanic plexus. The mucous membrane lining the middle ear cavity invests all the contents and forms several vascular folds which project into the cavity. This gives the cavity a honeycombed appearance.

15. BOUNDARIES The Roof or Tegmental Wall 1.The roof separates the middle ear from the middle cranial fossa. It is formed by a thin plate of bone called the tegmen tympani . This plate is prolonged backwards as the roof of the canal for the tensor tympani 2.In young children, the roof presents a gap at the unossified petrosquamous suture where the middle ear is in direct contact with the meninges. In adults, the suture is ossified and transmits a vein from the middle ear to the superior petrosal sinus. The Floor or Jugular Wall The floor is formed by a thin plate of bone which separates the middle ear from the superior bulb of the internal jugular vein. This plate is a part of the temporal bone . Near the medial wall the floor presents the tympanic canaliculus which transmits the tympanic branch of the glossopharyngeal nerve to the medial wall of the middle ear.

16. The Anterior or Carotid Wall The anterior wall is narrow due to the approximation of the medial and lateral walls, and because of descent of the roof. The uppermost part of the anterior wall bears the opening of the canal for the tensor tympani. The middle part has the opening of the auditory tube. The inferior part of the wall is formed by a thin plate of bone which forms the posterior wall of the carotid canal. The plate separates the middle ear from the internal carotid artery. This plate of bone is perforated by the superior and inferior sympathetic carotico tympanic nerves and the tympanic branch of the internal carotid artery. The bony septum between the canals for the tensor tympani and for the auditory tube is continued posteriorly on the medial wall as a curved lamina called the processus cochlea riformis . Its posterior end forms a pulley around which the tendon of the tensor tympani turns laterally to reach the upper part of the handle of the malleus.

17. Posterior or Mastoid Wall The posterior wall presents these features from above downwards 1.Superiorly, there is an opening or aditus through which the epitympanic recess communicates with the mastoid or tympanic antrum 2.The fossa incudis is a depression which lodges the short process of the incus. 3.A conical projection, called the pyramid , lies near the junction of the posterior and medial walls. It has an opening at its apex for passage of the tendon of the stapedius muscle. 4.Lateral to pyramid and near the posterior edge of the tympanic membrane, there is the posterior canaliculus for the chorda tympani through which the nerve enters the middle ear cavity.

18. The Lateral or Membranous Wall 1. The lateral wall separates the middle ear from the external acoustic meatus. It is formed: (a) Mainly by the tympanic membrane along with the tympanic ring and sulcus and (b) partly by the squamous temporal bone, in the region of the epitympanic recess. 2. Near the tympanic notch there are two small apertures, (a) The petrotympanic fissure lies in fronl of the upper end of the bony rim. It lodges the anterior process of the malleus and transmits the tympanic branch of the maxillary artery, (b) The anterior canaliculus for the chorda tympaninerve lies either in the fissure or just in front of it. The nerve leaves the middle ear through this canaliculus tc emerge at the base of the skull.

19. The Medial or Labyrinthine Wall The medial wall separates the middle ear from the internal ear. It presents the following features. The promontory is a rounded bulging produced by the first turn of the cochlea. It Is grooved by the tympanic plexus The fenestra vestibuli is an oval opening posterosuperior to the promontory. It leads into the vestibule of the internal ear and is closed by the footplate of the stapes. The prominence of the facial canal runs backwards just above the fenestra vestibuli, to reach the lower margin of the aditus . The canal then descends behind the posterior wall to end at the stylomastoid foramen. The fenestra cochleae is a round opening at the bottom of a depression posteroinferior to the promontory. It opens into the scala tympani of the cochlea, and is closed by the secondary tympanic membrane. The sinus tympani is a depression behind the promontory, opposite the ampulla of the posterior semicircular canal.

20. Contents of middle ear 1. Ear ossicles 2.Ligaments of ear ossicles 3.Tensor tympani and stapedius muscle 4.Vessels supplying and draining the middle ear 5.Nerves – chorda tympani and tympanic plexus 6. Air

21. THE EAR OSSICLES 3 in number – malleus , incus , stapes Malleus The malleus is so called because it resembles a hammer. It is the largest, and the most laterally placed ossicle. It has the following parts, (a) The rounded head lies in the epitympanic recess. It articulates posteriorly with the body of the incus. It provides attachment to the superior and lateral ligaments, (b) The neck lies against the pars flaccida and is related medially to the chorda tympani nerve. (c) The anterior process is connected to the petrotympanic fissure by the anterior ligament. (d) The lateral process projects from the upper end of the handle and provides attachment to the malleolar folds, (e) The handle extends downwards, backwards and medially, and is attached to the upper half of the tympanic membrane

22. Incus or Anvil It is so called because it resembles an anvil, used by blacksmiths. It resembles a molar tooth and has the following parts, (a) The body is large and bears an articular surface that is directed forwards. It articulates with the head of the malleus, (b) The long process projects downwards just behind and parallel with the handle of the malleus. Its tip bears a lentiform nodule directed medially which articulates with the head of the stapes.

23. Stapes This bone is so called because it is shaped like a stirrup. It is the smallest, and the most medially placed ossicle of the ear. It has the following parts, (a) The small head has a concave facet which articulates with the lentiform nodule of the incus, (b) The narrow neck provides insertion, posteriorly, to the thin tendon of the stapedius. (c) Two limbs or crura; anterior, the shorter and less curved; and posterior, the longer which diverge from the neck and are attached to the footplate, (d) The footplate, a foot piece or base, is oval in shape, and fits into the fenestra vestibuli.

24. Joints of the Ossicles (1)The incudomalleolar joint is a saddle joint. (2)The incudostapedial joint is a ball and socket joint. Both of them are synovia! joints. They are surrounded by capsular ligaments. Accessory ligaments are three for the malleus, and one each for the incus and the stapes which stabilize the ossicles. All ligaments are extremely elastic Muscles of the Middle Ear There are two muscles, the tensor tympani and the stapedius. Both act simultaneously to damp down the intensity of high-pitched sound waves and thus protect the internal ear.

25. Arterial Supply The main arteries of the middle ear are as follows. 1. The anterior tympanic branch of the maxillary artery which enters the middle ear through the petrotympanic fissure. 2. The posterior tympanic branch of the stylo mastoid branch of the posterior auricular artery which enters through the stylomastoid foramen. Venous Drainage Veins from the middle ear drain into the superior petrosal sinus and the pterygoid plexus of the veins. Lymphatic Drainage Lymphatics pass to the preauricular and retro pharyngeal lymph nodes. Nerve Supply The nerve supply is derived from the tympanic plexus which lies over the promontory.

26. TYMPANIC OR MASTOID ANTRUM Mastoid antrum is a small, circular, air filled space situated in the posterior part of the petrous temporal bone. It is of adult size at birth, size of a small pea, or 1 cm in diameter and has a capacity of about one mililitre .

27. Boundaries 1.Superiorly: Tegmen tympani, and beyond it the temporal lobe of the cerebrum. 2.Interiorly: Mastoid process containing the mastoid air cells. 3.Anteriorly: It communicates with the epitympanic recess through the aditus . The aditus is related medially to the ampullae of the superior and lateral semicircular canals, and posterosuperiorly to the facial canal. 4.Posteriorly: It is separated by a thin plate of bone from the sigmoid sinus. Beyond the sinus there is the cerebellum. 5.Medially: Petrous temporal bone

28. Internal Ear The internal ear, or labyrinth, lies in the petrous part of the temporal bone. It consists of the bony labyrinth within which there is a membranous labyrinth. The membranous labyrinth is filled with a fluid called endolymph. It is separated from the bony labyrinth by another fluid called the perilymph.

29. Bony Labyrinth The bony labyrinth consists of three parts: (a) The cochlea anteriorly (b) the vestibule, in the middle (c) the semicircular canals posteriorly

30. Cochlea The bony cochlea resembles the shell of a common snail. It forms the anterior part of the labyrinth. It has a conical central axis known as the modiolus around which the cochlear canal makes two and three quarter turns. A spiral ridge of the bone, the spiral lamina, projects from the modiolus and partially divides the cochlear canal into the scala vestibuli above, and the scala tympani below. The scala vestibuli communicates with the scala tympani at the apex of the cochlea by a small opening, called the helicotrema

31. Vestibule This is the central part of the bony labyrinth. It lies medial to the middle ear cavity. Its lateral wall opens into the middle ear at the fenestra vestibuli which is closed by the footplate of the stapes. Three semicircular canals open into its posterior wall. The medial wall is related to the internal acoustic meatus, and presents the spherical recess in front, and the elliptical recess behind. The two recesses are separated by a vestibular crest which splits inferiorly to enclose the cochlear recess . Just below the elliptical recess there is the opening of a diverticulum, the aqueduct of the vestibule which opens at a narrow fissure on the posterior aspect of the petrous temporal bone, posterolateral to the internal acoustic meatus.

32. Semicircular Canals There are three bony semicircular canals: An anterior or superior, posterior and lateral. They lie postero superior to the vestibule, and are set at right angles to each other. Each canal describes two-thirds of a circle, and is dilated at one end to form the ampulla. Three canals open into the vestibule by five openings.

33. The anterior or superior semicircular canal lies in a vertical plane at right angles to the long axis of the petrous temporal bone. It is convex upwards. Its position is indicated by the arcuate eminence seen on the anterior surface of the petrous temporal bone. Its ampulla is situated anterolaterally. Its posterior end unites with the upper end of the posterior canal to form the crus commune which opens into the medial wall of the vestibule. The posterior semicircular canal also lies in a vertical plane parallel to the long axis of the petrous temporal bone. It is convex backwards. Its ampulla lies at its lower end. The upper end joins the anterior canal to form the crus commune. The lateral semicircular canal lies in the horizontal plane with its convexity directed posterolaterally . The ampulla lies anteriorly, close to the ampulla of the anterior canal.

34. Membranous Labyrinth It is in the form of a complicated, but continuous closed cavity filled with endolymph. Parts of the epithelium of the membranous labyrinth are specialized to form receptors for sound organ of Corti, for static balance the maculae, and for kinetic balance the cristae. The membranous labyrinth consists of three main parts: (a) The spiral duct of the cochlea or organ of hearing, anteriorly; (b) the utricle and saccule the organs of static balance, within the vestibule; (c) the semicircular ducts the organs of kinetic balance, posteriorly

35. The Duct of the Cochlea or the Scala Media The spiral duct occupies the middle part of the cochlear canal between the scala vestibuli and the scala tympani. It is triangular in cross-section. The floor is formed by the basilar membrane; the roof by the vestibular or Reissner's membrane; and the outer wall by the bony wall of the cochlea. The basilar membrane supports the spiral organ of Corti which is the end organ for hearing .

36. The organ of Corti is innervated by peripheral processes of bipolar cells located in the spiral ganglion. This ganglion is located in the spiral canal present within the modiolus at the base of the spiral lamina. The central processes of the ganglion cells form the cochlear nerve. Posteriorly the duct of the cochlea is connected to the saccule by a narrow ductus reuniens . The sound waves reaching the endolymph through the vestibular membrane make appropriate parts of the basilar membrane vibrate, so that different parts of the organ of Corti are stimulated by different frequencies of sound. The loudness of the sound depends on the amplitude of vibration.

37. Saccule and Utricle The saccule lies in the anteroinferior part of the vestibule, and is connected to the basal turn of the cochlear duct by the ductus reuniens . The utricle is larger than the saccule and lies in the posterosuperior part of the vestibule. It receives three semicircular ducts through five openings. The duct of the saccule unites with the duct of the utricle to form the ductus endolymphaticus . The ductus endolymphaticus ends in a dilatation, the saccus endolymphaticus . The ductus and saccus occupy the aqueduct of the vestibule. The medial walls of the saccule and utricle are thickened to form a macula in each chamber. The maculae are end organs that give information about the position of the head. They are static balance receptors. They are supplied by peripheral processes of neurons in the vestibular ganglion

38. Semicircular Ducts The three semicircular ducts lie within the corresponding bony canals. Each duct has an ampulla corresponding to Tunnel between rods of Corti that of the bony canal. In each ampulla, there is an end organ called the ampullary crest or crista. Cristae respond to pressure changes in the endolymph caused by movements of the head.

39. Blood Supply of Labyrinth The arterial supply is derived mainly from the labyrinthine branch of the basilar artery which accompanies the vestibulocochlear nerve; and partly from the stylomastoid branch of the posterior auricular artery. The labyrinthine vein drains into the superior petrosal sinus or the transverse sinus. Other inconstant veins emerge at different points and open separately into the superior and inferior petrosal sinuses and the internal jugular vein.