Anatomy of Ear

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1. BY Dr. vibhash kumar vaidya ANATOMY OF EAR

2. EAR The ear is the organ of hearing. It plays an important role in maintaining the balance (equilibrium) of the body. The ear is divided into three parts: 1 . External ear. 2 . Middle ear. 3 . Internal ear.

3. EXTERNAL EAR The external ear consists of: ( a) pinna or auricle and, ( b) external auditory meatus. [which are concerned with collection and transmission of sound waves to the tympanic membrane.]

4. AURICLE/PINNA The auricle is trumpet-like wave like pattern of projection on the side of the head. The entire pinna except its lobule is made up of a single piece of yellow elastic cartilage covered with skin. The lobule of pinna is made of fibrofatty tissue covered with skin. The auricular cartilage is continuous with the cartilage of the external auditory meatus .

5. FEATURES The auricle presents two surfaces: lateral and medial . The lateral surface of auricle displays following elevations and depressions : Concha – A large depression that leads into the external auditory meatus. Helix - forms a prominent peripheral rim of the pinna. It consists of two limbs—anterior and posterior. An anterior limb ends as crus of helix. The posterior limb ends below as flabby ear lobe and its upper end sometimes presents a small elevation called Darwin’s tubercle.

6. Antihelix - is another prominent ridge present in front and parallel to the posterior part of helix, partly encircling the concha. Its upper end divides into two crura enclosing a triangular depression called triangular fossa. The narrow gutter between the helix and antihelix is called scaphoid fossa. Tragus - is a small triangular flap in front of concha. Antitragus - is a small elevation opposite to tragus from which it is separated by an intertragic notch. Cymba conchae - is a small area of concha above the crus of helix. Lobule - of the ear hangs below the antitragus as a large skin covered flap of fibrofatty tissue.

7. The medial/cranial surface of (pinna) presents the following features: 1 . Eminentia concha - which corresponds to the depression of the concha. 2 . Eminentia triangularis - which corresponds to the triangular fossa between the crura of the antihelix.

8. EXTERNAL AUDITORY MEATUS The external auditory meatus (syn. external acoustic meatus) extends from the bottom of the concha to the tympanic membrane. Measures- about 24 mm along its posterior wall. It is not a straight tube but it has a typical S-shaped course. Its outer part is directed upwards, backwards, and medially (UBM), whereas its inner part is directed downwards, forwards, and medially (DFM ). Therefore , to examine the tympanic membrane the pinna has to be pulled upwards, backwards, and laterally, to bring the two parts in alignment. Parts outer 1/3 (8 mm) inner two-third (16 mm)

9. TYMPANIC MEMBRANE The tympanic membrane (or ear drum) is a thin (0.1 mm thick) semitransparent membrane. It is forms the partition between external acoustic meatus and middle ear. It is oval in shape. Measurements: 9–10 mm in length, and 8–9 mm in width. It is placed obliquely making an angle of about 55° with the floor of the external acoustic meatus. The tympanic membrane faces downwards, forwards, and laterally as though to catch the sounds reflected from the ground.

10. Structure : The tympanic membrane is made of three layers. Outer cuticular layer Middle fibrous layer Innermucosal layer

11. CLINICAL CORRELATION The infection and boils of the external auditory meatus cause very little swelling but are very painful because the skin lining is firmly adhered to the underlying cartilage and bone . Ear wax : - It prevents the injury of the lining epithelium of the external auditory meatus from water and the damage of tympanic membrane by trapping the insects. The excess of ear wax interfering with hearing. Perforation of the tympanic membrane : - It may result from an external injury or middle ear infection (otitis media).

12. MIDDLE EAR The middle ear (syn. tympanum, tympanic cavity) is a narrow slit-like air-filled cavity within the petrous part of the temporal bone. The middle ear is sandwiched between the external and internal ear. It contains three auditory ossicles, which transmit sound vibrations from tympanic membrane in its lateral wall to the internal ear.

13. From front to back, the diverticulum consists of pharyngotympanic tube, tympanic cavity, and mastoid antrum. In a section through long axis of petromastoid bone, the outline of tympanic cavity together with mastoid antrum and pharyngotympanic tube resembles a pistol .

14. Size and Shape - The middle ear is shaped like a cube, compressed from side to side. In coronal section, it resembles a biconcave disc, like a red blood cell. Measurements - Vertical diameter: 15 mm. Anteroposterior diameter: 15 mm. Transverse diameters: ( a) At roof: 6 mm . ( b) In the center: 2 mm . ( c) At the floor: 4 mm .

15. Communication The middle ear: Anteriorly with nasopharynx through pharyngotympanic tube. Posteriorly with mastoid antrum and mastoid air cells through aditus to antrum called aditus ad antrum. Contents of the Middle Ear: Inside the mucous lining: 1 . Air. Outside the mucous lining: 1 . Three small bones called ear ossicles: malleus, incus, and stapes. 2 . Two muscles: tensor tympani and stapedius. 3 . Two nerves: chorda tympani and tympanic plexus. 4 . Vessels supplying and draining the middle ear. 5 . Ligaments of the ear ossicles.

16. SUBDIVISIONS OF THE MIDDLE EAR 1 . Epitympanum - a part above the tympanic membrane containing head of malleus, body, and short process of incus. 2 . Mesotympanum - a part opposite to tympanic membrane containing handle of malleus, long process of incus, and stapes. It is the narrowest part of the middle ear. 3 . Hypotympanum - a part below the tympanic membrane.

17. BOUNDARIES The middle ear is likened to a six-sided box and thus presents six walls: 1 . Roof. 2 . Floor. 3 . Anterior wall. 4 . Posterior wall. 5 . Medial wall. 6 . Lateral wall . O- oval window, P- pyramid, PC- processus cochleariformis , PM-promontory, R- round window, S- sinus tympani, TP- tympanic plexus

18. CLINICAL CORRELATION Infection of the middle ear (otitis media ): - It is common especially in infants and children. Infective agents reach the middle ear from the upper respiratory tract through pharyngotympanic tube. The long-standing infection leads to chronic suppurative otitis media (CSOM ). Which clinically presents as ear discharge and perforation of tympanic membrane. The spread of infection from the middle ear may give rise to the following clinical conditions : – Acute mastoiditis and mastoid abscess, when infection spreads into mastoid antrum and mastoid air cells through aditus ad antrum in the posterior wall . – Meningitis and temporal lobe abscess may occur, if infection spreads upwards through the thin roof ( tegmen tympani ). – Lower motor neuron type of facial palsy, when infection erodes the papery thin bony wall of facial canal . – Transverse and sigmoid sinus thrombosis, when infection spreads through the floor.

19. INTERNAL EAR The internal ear consists of a closed system of fluid filled intercommunicating membranous sacs and ducts called membranous labyrinth. The fluid filled in the membranous labyrinth is called endolymph . The membranous labyrinth lies within the complex intercommunicating bony cavities and canals (bony labyrinth) in the petrous part of the temporal bone. The space between the membranous and bony labyrinth is filled with fluid called perilymph. The sensory receptors within the membranous labyrinth are responsible for hearing and balancing (equilibrium).

20. Components of the Internal Ear The internal ear consists of two components: 1 . Membranous labyrinth. 2 . Bony labyrinth .

21. MEMBRANOUS LABYRINTH The membranous labyrinth consists of the following four parts: 1 . Cochlear duct. 2 . Saccule . 3 . Utricle. 4 . Semicircular ducts (three ). Complete membranous labyrinth. Parts of membranous labyrinth.

22. BONY LABYRINTH The bony labyrinth consists of a series of intercommunicating bony cavities and canals within the petrous part of the temporal bone . Parts - The bony labyrinth presents three parts from before backwards these are: 1. Cochlea. 2 . Vestibule. 3 . Semicircular canals (three).

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