MIDDLE EAR

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By: venkateswara rao0625 (26 month(s) ago)

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Middle Ear :

Middle Ear Dr. Pankaj Maheria

PowerPoint Presentation:

The middle ear or tympanic cavity is contained within the petrous part of temporal bone. It is filled with air and lined by mucous membrane. It assumes full adult size at birth. Communication : Lateral wall of naso- pharynxv - auditory tube Mastoid antrum – aditus to the antrum

PowerPoint Presentation:

Sandwiched between external and internal ears Coronal section : biconcave disc like red blood cell Section through the long axis of petro-mastoid bone, the outline of the auditory tube together with tympanic cavity and mastoid antrum resembles pistol - the nozzle being represented by auditory tube, the body by the tympanic cavity and the handle by the mastoid antrum.

PowerPoint Presentation:

Contains: A chain of three ossicles Malleus Incus stapes Two muscles Tensor tympani Stapedius Blood vessels and nerves Six sets of arteries ; Four sets of nerves.

Protection of the tympanic cavity:

Protection of the tympanic cavity Auditory tube which maintains an equilibrium of air pressure on each side of the tympanic membrane Shape of the articular surfaces between the ossicles Reflex contraction of tensor tympani and stapedius which prevents damage during sudden explosive sounds.

Measurements:

Measurements Vertical and antero-posterior diameters: 15 mm each - Transverse diameters 6 mm (at the roof) 2 mm (opposite the centre of tympanic membrane) 4 mm (at the floor)

Subdivisions:

Subdivisions Epitympanum (attic) – Above the tympanic membrane It contains head of malleus, and the body and short process of incus Mesotympanum Opposite the tympanic membrane The narrowest part Contains the handle of malleus, long process of incus and the stapes

Subdivisions:

Subdivisions Hypotympanum – below the membrane,

Boundaries of tympanic cavity :

Boundaries of tympanic cavity Roughly cuboidal Six walls Roof Floor Anterior Posterior Medial Lateral

Boundaries of tympanic cavity :

Boundaries of tympanic cavity The roof is wider than the floor The anterior wall is narrower than its posterior wall The medial and lateral walls project with their convexities towards the tympanic cavity making the interior an hour­glass constriction.

ROOF (tegmental wall):

ROOF (tegmental wall) Formed by the tegmen tympani which is a thin plate of bone of petrous temporal and intervenes between the tympanic cavity and the middle cranial fossa. The bony plate is pierced by the lesser and greater petrosal nerves.

Applied anatomy:

Applied anatomy The tegmen tympani may remain unossified in the young through which infection from the tympanic cavity may extend to the cerebral meninges. In the adult, the veins from the tympanic cavity sometimes drain into the superior petrosal sinus through the persistent petrosquamous suture in the roof, and thus spread the infection in the intracranial sinuses.

FLOOR (jugular wall):

FLOOR (jugular wall) formed by the jugular fossa on the undersurface of petrous part of temporal bone Related with the superior bulb of the internal jugular vein.

FLOOR (jugular wall):

FLOOR (jugular wall) In some places the bony fossa may be deficient, where the tympanic cavity is separated from the vein only by the mucous membrane and fibrous tissue. Sometimes the floor is thickened and invaded by the accessory mastoid air cells.

FLOOR (jugular wall):

FLOOR (jugular wall) Tympanic canaliculus: Tympanic branch of glossopharyngeal nerve pierces the floor, and enters the tympanic cavity through an Tympanic canaliculus between the jugular fossa and lower opening of the carotid canal.

ANTERIOR WALL (Carotid wall):

ANTERIOR WALL (Carotid wall) Lower part: Posterior wall of the bony carotid canal, Perforated by the superior and inferior carotico-tympanic vessels and nerves.

ANTERIOR WALL (Carotid wall):

ANTERIOR WALL (Carotid wall) Upper part Two parallel bony canals, one above the other Upper canal for the tensor tympani muscle Lower canal for the bony part of the auditory tube.

POSTERIOR WALL (Mastoid wall):

POSTERIOR WALL (Mastoid wall) It is wider above than below, and presents the following features : Aditus to the mastoid antrum Fossa incudis

POSTERIOR WALL (Mastoid wall):

POSTERIOR WALL (Mastoid wall) Vertical bony canal through which facial nerve descends upto the stylo-mastoid foramen.

POSTERIOR WALL (Mastoid wall):

POSTERIOR WALL (Mastoid wall) Pyramidal eminence contains stapedius muscle and its nerve supply. At apex a pin-point opening through which the tendon of the stapedius passes forward to the neck of the stapes.

MEDIAL WALL (Labyrinthine wall):

MEDIAL WALL (Labyrinthine wall) Faces towards the bony labyrinth of the internar ear and presents the following features: Promontory Rounded elevation produced by the basal turn of the cochlea of the internal ear. Tympanic branch of the glossopharyngeal nerve ramifies on the promontory and forms the tympanic plexus.

MEDIAL WALL (Labyrinthine wall):

MEDIAL WALL (Labyrinthine wall) Fenestra Vestibuli (fenestra ovalis) Reniform aperture which is situated behind and above the promontory. The opening is closed in the recent state by the base of the stapes and annular ligament.

MEDIAL WALL (Labyrinthine wall):

MEDIAL WALL (Labyrinthine wall) Fenestra Cochleae (fenestra rotunda) Small window below and behind the promontory is closed in the recent state by a trilaminar secondary tympanic membrane which separates the tympanic cavity from the scala tympani of the internal

MEDIAL WALL (Labyrinthine wall):

MEDIAL WALL (Labyrinthine wall) Sinus tympani A depression behind the promontory Indicates the position of the ampulla of the posterior semicircular canal. The area of the medial wall in front of the promontory is closely related to the apex of the cochlea.

MEDIAL WALL (Labyrinthine wall):

MEDIAL WALL (Labyrinthine wall) Oblique part of facial nerve canal Extends backward and downward above the fenestra vestibuli Until it joins the vertical part of bony canal along posterior wall of the tympanum.

MEDIAL WALL (Labyrinthine wall):

MEDIAL WALL (Labyrinthine wall) Processus trochleariformis A hook like process Derived from backward extension of the bony partition intervening between the canals for the tensor tymani and the auditory tube. The tendon of tensor tympani turns laterally around this process before its insertion into the handle of malleus.

Lateral wall (Membranous wall):

Lateral wall (Membranous wall) Formation : Mucous covered medial surface of the tympanic membrane Presents a convexity towards the tympanic cavity Umbo : Maximum point of convexity .

Lateral wall (Membranous wall):

Lateral wall (Membranous wall) Tympanic membrane’s attachment: Handle of the malleus

Lateral wall (Membranous wall):

Lateral wall (Membranous wall) Chorda tympani nerve crosses the medial side of the handle of the malleus at the junction of pars flaccida and pars tensa of the tympanic membrane.

Lateral wall (Membranous wall):

Lateral wall (Membranous wall) Close to the anterior margin of the tympanic membrane, the lateral wall presents a slit-like opening, the petrotympanic fissure, Anterior canaliculus Posterior canaliculus

PowerPoint Presentation:

The Epitympanic part of the lateral wall Squamous part of the temporal bone. Contains: Head and anterior process of the malleus Body and short process of the incus.

Tympanic membrane Ear-drum:

Tympanic membrane Ear-drum An oval, semi-transparent, pearly grey trilaminar membrane and separates the tympanic cavity from the external acoustic meatus. Diameter measures Maximum about 9-10 mm, and minimum 8-9 mm

POSITION:

POSITION Placed obliquely An acute angle of about 55°with the floor of the external acoustic meatus. In the newborn, the membrane is almost horizontal; hence a child can withstand noisy sound better than adult.

POSITION:

POSITION Fibro-cartilaginous ring Sulcus of the tympanic plate Deficient above

SUBDIVISIONS of the membrane :

SUBDIVISIONS of the membrane The malleolar folds divide the tympanic membrane into two parts :- Pars flacdda: A small, triangular lax area above the malleolar folds Sometimes it presents a small perforation.

SUBDIVISIONS of the membrane :

SUBDIVISIONS of the membrane Pars tensa Occupies rest of membrane Rendered taut by the attachment of the handle of the malleus and by the disposition of radiating fibres of the intermediate layer from the handle

SURFACES OF THE MEMBRANE:

SURFACES OF THE MEMBRANE Medial surface: Convex and bulges toward the tympanic cavity Maximum point of convexity is known as the umbo,. Attachment : Handle of malleus

SURFACES OF THE MEMBRANE:

SURFACES OF THE MEMBRANE Lateral surface: Concave and directed downward, forward and laterally As a result, the anterior wall and the floor of the external meatus are longer than the posterior wall and the roof.

Structure of membrane:

Structure of membrane Outer cuticular layer Intermediate fibrous layer Inner mucous layer

PowerPoint Presentation:

THREE RECESSES :- Anterior recess : Between handle of malleus and an anterior fold Contain: chorda tympani nerve

PowerPoint Presentation:

THREE RECESSES :- Posterior recess Between handle of malleus and a posterior fold Contain: chorda tympani nerve

PowerPoint Presentation:

THREE RECESSES :- Prussak' s pouch Mucous recess above the lateral process of malleus and intervening between the neck off malleus and pars flaccida of tympanic membrane.

Arterial supply:

Arterial supply Deep auricular branch of maxillary artery Stylomastoid branch of the posterior auricular and anterior tympanic branch maxillary arteries

Venous drainage:

Venous drainage Outer layer: External jugular vein Inner layer Transverse sinus and pterygoid venous plexus.

Nerve supply:

Nerve supply Cuticular layer Auriculo-temporal nerve: Upper and anterior part of the membrane; Auricular branch of vagus nerve Lower and posterior part of the membrane; Mucous layer Glossopharyngeal nerve through the tympanic plexus.

EXTERNAL EXAMINATION:

EXTERNAL EXAMINATION Cone of light Antero-inferior quadrant of the membrane. Beneath the membrane: Handle of malleus White prominence : lateral process of malleus Long process of incus is often seen as a white streak behind and parallel to the upper part of the handle of malleus.

DEEP RELATIONS:

DEEP RELATIONS Antero-inferior quadrant Carotid canal Antero-superior quadrant Tympanic opening of the auditory tube

DEEP RELATIONS:

DEEP RELATIONS Postero-superior quadrant – Long process of incus, stapes and fenestra vestibuli Postero-inferior quadrant – promontory and fenestra cochleae.

APPLIED ANATOMY:

APPLIED ANATOMY Myringotomy A surgical incision of the membrane Made in the postero-inferior part in order to avoid injury of the chorda tympani nerve and the ossicles of the ear.

The malleus (L. a hammer):

The malleus (L. a hammer) Head Neck Process Handle or manubrium Lateral Anterior Malleus functions as a lever, with the longer of its two processes and its handle attached to the tympanic membrane

Incus :

Incus L. an anvil Located between the malleus and the stapes and articulates with them Part Body Two limbs Long limb : parallel to the handle of the malleus Short limb : connected by a ligament to the posterior wall of the tympanic cavity.

Stapes:

Stapes L. a stirrup The smallest ossicle. Part : Head two limbs (crura) Base

Ossification:

Ossification One centre in the fourth month of intrauterine life. All auditory ossicles assume adult size at birth.

Joints of the ossicles:

Joints of the ossicles Incudomalleolar joint Saddle joint Incudostepedial joint Ball socket

Tensor tympani:

Tensor tympani Origin: Cartilaginous part of the auditory tube Sulcus tubac Insertion : Root of the handle of malleus.

PowerPoint Presentation:

Nerve supply Trunk of the mandibular nerve Action : It draws the handle of malleus medially and tightens the tympanic membrane.

Stapedius:

Stapedius An asymmetrical bipennate muscle Origin : Pyramidal eminence on the posterior wall of tympanic cavity. Insertion : Posterior surface of neck of stapes

Stapedius:

Stapedius Nerve supply : Facial nerve Action: Draws the stapes laterally.

Applied anatomy:

Applied anatomy Hyperacusis Otosclerosis

ARTERIES OF THE MIDDLE EAR:

ARTERIES OF THE MIDDLE EAR Six sets of arteries supply the tympanic cavity Stylomastoid branch of posterior auricular (or occipital) artery Anterior tympanic branch of maxillary artery Petrosal branch of middle meningeal artery

ARTERIES OF THE MIDDLE EAR:

ARTERIES OF THE MIDDLE EAR Six sets of arteries supply the tympanic cavity Superior tympanic branch of middle meningeal artery Branches from ascending pharyngeal artery and artery of the pterygoid canal Tympanic branches of internal carotid artery

NERVES OF THE MIDDLE EAR:

NERVES OF THE MIDDLE EAR Four sets of nerves are encountered in the tympanic cavity:- Superior and inferior carotico-tympanic nerves Tympanic branch of glossopharyngeal nerve

NERVES OF THE MIDDLE EAR:

NERVES OF THE MIDDLE EAR Four sets of nerves are encountered in the tympanic cavity:- Chorda tympani nerve Facial nerve

Applied anatomy:

Applied anatomy Otitis Media

Mastoid antrum:

Mastoid antrum Air sinus in the petrous part of temporal bone. Assume adult size at birth Each walls mesures about 10 mm Capcity 1 ml Non ciliated falttened cells

Boundaries::

Boundaries: Roof: Tegmen tympani Floor Opening of mastoid air cells Anterior wall Upper part: Aditus of the antrum Lower part: canal for facial nerve

Boundaries::

Boundaries: Posterior wall Sigmoid sinus Medial wall Semicircular canal

Boundaries::

Boundaries: Lateral wall Squamuous part of temporal bone. Thickness of lateral wall: 2 mm in new born Increase by 1 mm each year until it become 12 to 15 mm by puberty

Mastoid air cell:

Mastoid air cell Types of mastoid process Pneumatic type: Sclerotic type Mixed type

PowerPoint Presentation:

Artery Posterior tympanic artery a branch of stylomastoid branch of posterior auricular artery Vein: Mastoid emissary vein Posterior auricular vein Sigmoid sinus

PowerPoint Presentation:

Lymphatic: Posterior auricular to upper deep cervical lymph nodes Nerve supply: Tympanic plexus Meningeal branch of mandibular nerve.

PowerPoint Presentation:

Thank you