anatomy of external ear and middle ear

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ANATOMY OF THE EXTERNAL EAR:

ANATOMY OF THE EXTERNAL EAR

THE EXTERNAL EAR:

THE EXTERNAL EAR Consists of Auricle/ Pinna External auditory meatus

Auricle / Pinna:

Auricle / Pinna The lateral surface of the auricle has characteristic prominences and depressions which are different in every individual even among identical twins. comparable to fingerprints allow the identification of persons on the physiognomy of their auricles. The medial (cranial) surface of the auricle has elevations corresponding to the depressions on the lateral surface

Pinna: Parts :

Pinna : Parts Helix The curved rim often has a small prominence (Darwin's tubercle) at its posterosuperior aspect Antihelix Another prominence Anterior and parallel to the helix Triangular Fossa Superiorly, antihelix divides into two crura between them is the triangular fossa

Pinna: Parts :

Pinna : Parts Scaphoid fossa lies above the superior crura . Concha In front of the antihelix , and partly encircled by it This is divided into two portions by the descending limb of the anterior superior portion of the helix. The smaller superior portion is the Cymba Conchae and is the direct lateral relation to the Suprameatal triangle of the temporal bone. The larger inferior portion is known as the Cavum Conchae

Pinna: Parts :

Pinna : Parts Tragus Below the crus of the helix and overlapping the external auditory meatus small blunt triangular prominence Antitragus Opposite the tragus Intertragic Notch separates the tragus from the antitragus . Lobule lies below the antitragus soft, being composed of fibrous and adipose tissue.

Pinna:

Pinna The body of the auricle is formed from Elastic Fibrocartilage Continuous plate except for a narrow gap between the tragus and the anterior crus of the helix, where it is replaced by a dense fibrous tissue; Incisura Terminalis This gap is the site for an endaural incision

Pinna: Cartilage :

Pinna : Cartilage The cartilage extends about 8 mm down the EAC to form its lateral third. The cartilage of the auricle is covered with perichondrium from which it derives its supply of nutrients, as cartilage itself is avascular . Stripping the perichondrium from the cartilage, as occurs following injuries that cause haematoma , can lead to cartilage necrosis with crumpled up 'boxer's ears'.

Pinna: Skin:

Pinna : Skin The skin of the pinna is thin and closely attached to the perichondrium on the lateral surface. On the medial (cranial) surface, there is a definite subdermal adipose layer that allows dissection during pinnaplasty surgery. The skin of the auricle is covered with fine hairs and, most noticeably in the concha and the scaphoid fossa , there are sebaceous glands opening into the root canals of these hairs. On the tragus and intertragic notch coarse, thick hair may develop in the middle-aged and older male.

Pinna:

Pinna The cartilage of the auricle is connected to the temporal bone by two extrinsic ligaments. The Anterior Ligament runs from the tragus and from a cartilaginous spine on the anterior rim of the crus of the helix to the root of the zygomatic arch. The Posterior Ligament runs from the medial surface of the concha to the lateral surface of the mastoid prominence. Intrinsic ligaments connect various parts of the cartilaginous auricle

Pinna: Muscles:

Pinna : Muscles Extrinsic and intrinsic muscles are attached to the perichondrium of the cartilage. The intrinsic muscles - six in number – are small, inconsistent and without useful function. There are three extrinsic muscles: auricularis anterior, superior and posterior All three radiate out from the auricle to insert into the epicranial aponeurosis .

Pinna:

Pinna Temporal and posterior auricular branches of the facial nerve supply the extrinsic muscles and, while being functionally unimportant, they do give rise to the Post-auricular Myogenic Response following appropriate auditory stimulation.

Pinna: Blood Supply:

Pinna : Blood Supply Arterial branches of the external carotid supply the auricle. The Posterior Auricular is the dominant artery and supplies The medial surface (except the lobule) The concha The middle and lower portions of the helix The lower part of the antihelix

Pinna: Blood Supply:

Pinna : Blood Supply The Anterior Auricular branches of the superficial temporal supply the upper portions of the helix and antihelix triangular fossa tragus lobule. The Superior Auricular Artery has a constant course and connects the superior temporal artery and the posterior auricular artery network

Pinna: Nerve Supply:

Pinna : Nerve Supply Both cranial branchial nerves and somatic cervical nerves supply the auricle The Greater Auricular Nerve prevails on the lateral and medial

PowerPoint Presentation:

  Nerve   Derived from   Region Supplied   Greater Auricular   Cervical Plexus C2 C3   Medial surface and posterior part of lateral surface of pinna   Lesser occipital   Cervical plexus C2  Superior portion of medial surface   Auricular   Vagus   Concha and Antihelix   Auriculo temporal   Mandibular division of trigeminal nerve   Tragus, Crus of the helix and adjacent helix   Facial     Supplies root of concha

Pinna: Lymphatic Drainage :

Pinna : Lymphatic Drainage from the posterior surface is to the lymph nodes at the mastoid tip from the tragus and from the upper part of the anterior surface to the preauricular nodes from the rest of the auricle to the upper deep cervical nodes.

External Auditory Canal:

External Auditory Canal Extends from the concha of the auricle to the tympanic membrane Approximately 2.4 cm long The supporting framework of the canal wall is cartilage in the lateral one-third and bone in the medial two-thirds.

External Auditory Canal:

External Auditory Canal In adults, the cartilaginous portion runs inwards, slightly downwards and forwards. The canal is straightened, therefore, by gently moving the auricle upwards and backwards to counteract the direction of the cartilaginous portion. In the neonate, there is virtually no bony external meatus as the tympanic bone is not yet developed, and the tympanic membrane is more horizontally placed so that the auricle must be gently drawn downwards and backwards for the best view of TM

External Auditory Canal:

External Auditory Canal In the adult, the lateral cartilaginous portion is about 8 mm long and is continuous with the auricular cartilage. The bony canal wall, about 1.6 mm long, is narrower than the cartilaginous portion and itself becomes smaller closer to the tympanic membrane. The medial end of the bony canal is marked by a groove, the tympanic sulcus , which is absent superiorly.

External Auditory Canal:

External Auditory Canal Although the tympanic bone makes up the greater part of the canal, and also carries the sulcus , the squamous bone forms the roof. Therefore, there are two suture lines in the canal wall with the tympanosquamous anteriorly and the tympanomastoid posteriorly .

External Auditory Canal:

External Auditory Canal there are two constrictions: one at the junction of the cartilaginous and bony portions the other, the isthmus, 5 mm from the tympanic membrane Deep to the isthmus, the anteroinferior portion of the canal dips forward forming a wedge-shaped anterior recess between the tympanic membrane and the canal. This recess can be a difficult spot for access either in the clinic or at surgery

External Auditory Canal:

External Auditory Canal The external canal is lined with skin There is outward, oblique growth of the epidermis of the canal skin and pars flaccida so that the surface layers effectively migrate towards the external opening of the canal 0.1mm/day Skin of the pars tensa has a different derivation Create outward mass migration of the skin

External Auditory Canal:

External Auditory Canal However, if a hole is made in the tympanic membrane and a graft laid underneath the membrane (an underlay graft) then migration of the skin from the outer edge of the perforation is directed centrally to cover the graft. This occurs because the boundary conditions have altered and fortunately provides the basis for the healing of grafts and for the reepithelialization of mastoid cavities.

External Auditory Canal:

External Auditory Canal However, the property of canal skin to migrate can also bring problems with the formation of cholesteatoma if the skin becomes displaced into the middle ear cleft.

External Auditory Canal:

External Auditory Canal At the outer limits of the ear canal are some short hair that project towards the opening of the canal. In this region are clusters of ceruminous and sebaceous glands. Ceruminous glands Modified apocrine sweat glands Open into the root canal of the hair follicles Produce a watery, white secretion that slowly darkens, turning semi-solid and sticky as it dries. Respond to many stimuli such as adrenergic drugs, fever and emotion which, along with direct mechanical stimulation, can all produce an increase or altered secretion.

External Auditory Canal:

External Auditory Canal Sebaceous glands produce an oily material (sebum) from the breakdown of their fat-containing cells which is usually excreted into the root canals of the hair follicles. The mixture of desquamated cells, cerumen and sebum forms wax. Human earwax is a Mendelian trait consisting of wet and dry forms.

External Auditory Canal:

External Auditory Canal Dry wax, lacking cerumen , is yellowish or grey and brittle Wet wax is brownish and sticky. The wet phenotype is dominant over the dry type. A single nucleotide polymorphism in the ABCC11 gene is responsible for the determination of earwax type AA genotype corresponding to dry wax GA and GG to wet wax.

External Auditory Canal:

External Auditory Canal Arterial Supply of the external meatus is derived from branches of the external carotid. The auricular branches of the superficial temporal artery supply the roof and anterior portion of the canal. The deep auricular branch of the first part of the maxillary artery supplies the anterior meatal wall skin and the epithelium of the outer surface of the tympanic membrane. auricular branches of the posterior auricular artery supply the posterior portions of the canal.

External Auditory Canal:

External Auditory Canal The veins drain into the external jugular vein, the maxillary veins and the pterygoid plexus. The lymphatic drainage follows that of the auricle.

ANATOMY OF THE MIDDLE EAR CLEFT:

ANATOMY OF THE MIDDLE EAR CLEFT

Middle Ear Cleft:

Middle Ear Cleft The middle ear cleft consists of the tympanic membrane, tympanic cavity, the Eustachian tube and the mastoid air cell system. Tympanic cavity is an irregular, air-filled space within the temporal bone between the tympanic membrane laterally and the osseous labyrinth medially.

Tympanic Membrane:

Tympanic Membrane Lies at the medial end of the external auditory meatus Forms the majority of the lateral wall of the tympanic cavity. Slightly oval in shape, being broader above than below, forming an angle of about 55° with the floor of the meatus . Its longest diameter from posterosuperior to anteroinferior is 9-10mm, while perpendicular to this the shortest diameter is 8-9 mm.

Tympanic Membrane:

Tympanic Membrane Most of the circumference is thickened to form a fibrocartilaginous ring, the Tympanic Annulus, which sits in a groove in the tympanic bone, the Tympanic Sulcus . The sulcus does not extend into the Notch Of Rivinus at the roof of the canal, which is formed by part of the squama of the temporal bone. From the superior limits of the sulcus , the annulus becomes a fibrous band which runs centrally as Anterior And Posterior Malleolar Folds to the lateral process of the malleus

Tympanic Membrane:

Tympanic Membrane This leaves a small, triangular region of tympanic membrane above the malleolar folds within the notch of Rivinus , called the Pars Flaccida , which does not have a tympanic annulus at its margins. The Pars Tensa forms the rest of the tympanic membrane and is concave towards the ear canal The handle of malleus is clearly visible within the tympanic membrane. The tip of the malleus handle is attached at the Umbo at centre of the membrane

Tympanic Membrane:

Tympanic Membrane 3 layers outer epithelial layer, the epidermis, which is continuous with the skin of the external meatus ; middle, mainly fibrous layer, the lamina propria inner mucosal layer continuous with the lining of the tympanic cavity. The lamina propria of the pars tensa has radially oriented fibres in the outer layers and circular, parabolic and transverse fibres in the deeper layer. In the pars flaccida , the lamina propria is less marked and the orientation of the collagen fibres seems random.

Tympanic Membrane:

Tympanic Membrane The Arterial Supply arises from branches supplying both the external auditory meatus and the middle ear. Interconnect through extensive anastomoses within the connective tissue layer of the lamina propria . Epidermal vessels originate from the Deep Auricular branch of the Maxillary Artery coming from the external auditory meatus Mucosal vessels arise from the Anterior Tympanic branches of the Maxillary Artery, the Stylomastoid branch of the Posterior Auricular Artery and probably from the Middle Meningeal Artery

Tympanic Membrane:

Tympanic Membrane Nerve supply Branches of the Auriculotemporal nerve ( Vc ) Auricular branch of the Vagus Tympanic branch of the Glossopharyngeal nerve These also run in the lamina propria Both the vascular supply and innervation are relatively sparse in the middle part of the posterior half of the tympanic membrane.

Tympanic Cavity:

Tympanic Cavity Divided into three compartments: Epitympanum (Upper) Mesotympanum (middle) Hypotympanum (lower) Epitympanum or attic, lies above the level of the malleolar folds Hypotympanum lies below the level of the inferior part of the tympanic sulcus and is continuous with the mesotympanum above.

THE LATERAL WALL:

THE LATERAL WALL Formed by the bony lateral wall of the epitympanum superiorly, the tympanic membrane centrally and the bony lateral wall of the hypotympanum inferiorly The lateral epitympanic wall is wedge-shaped in section and its sharp inferior portion is also called the outer attic wall or scutum ( Latin:'shield ')

THE LATERAL WALL:

THE LATERAL WALL Three holes are present in the bone of the medial surface of the lateral wall of the tympanic cavity. The Petrotympanic Fissure Slit about 2 mm long It receives the anterior malleolar ligament Transmits the anterior tympanic branch of the maxillary artery to the tympanic cavity. The Chorda Tympani enters the medial surface of the fissure through a separate Anterior Canaliculus (Canal Of Huguier )

THE LATERAL WALL:

THE LATERAL WALL It then runs posteriorly between the fibrous and mucosal layers of the tympanic membrane The nerve reaches the posterior bony canal wall just medial to the tympanic sulcus , enters the Posterior Canaliculus and then runs through the posterior wall of the tympanic cavity until it reaches the facial nerve

THE ROOF:

THE ROOF The roof of the epitympanum is the Tegmen Tympani, a thin bony plate that separates the middle ear space from the middle cranial fossa . Both the petrous and squamous portions of the temporal bone form it Petrosquamous suture line, which does not close until adult life, can provide a route of access for infection into the extradural space in children.

THE FLOOR:

THE FLOOR Consist of compact or pneumatized bone and separates the hypotympanum from the dome of the jugular bulb. Occasionally, the floor is deficient and the jugular bulb is then covered only by fibrous tissue and a mucous membrane. At the junction of the floor and the medial wall of the cavity there is a small opening that allows the entry of the Tympanic Branch of the Glossopharyngeal Nerve

THE ANTERIOR WALL:

THE ANTERIOR WALL The Lower-Third of the anterior wall consists of a thin plate of bone covering the carotid artery. This plate is perforated by the superior and inferior caroticotympanic nerves carrying sympathetic fibres to the tympanic plexus, and by tympanic branches of the internal carotid artery. The Middle-third comprises the tympanic orifice of the Eustachian tube, which is oval and 5 x 2 mm in size. Just above this is a canal containing the tensor tympani muscle enclosed in a thin bony sheath. The Upper-third is usually pneumatized and may house the anterior epitympanic sinus, which can hide residual cholesteatoma in canal wall up surgery

THE MEDIAL WALL:

THE MEDIAL WALL The promontory is a rounded elevation occupying much of the central portion of the medial wall. It covers part of the basal coil of the cochlea has small grooves on its surface containing the nerves which form the tympanic plexus.

THE MEDIAL WALL:

THE MEDIAL WALL Behind and above the promontory is the Oval Window A nearly kidney-shaped opening Connects the tympanic cavity with the vestibule In life it is closed by the footplate of the stapes and its surrounding annular ligament. Its size varies with the size of the footplate But on average it is 3.25 mm long and 1.75 mm wide.

THE MEDIAL WALL:

THE MEDIAL WALL The Round Window Niche lies below and a little behind the oval window niche from which it is separated by a posterior extension of the promontory called the Subiculum . Occasionally, another ridge of bone – the Ponticulus - leaves the promontory above the subiculum and runs to the pyramid on the posterior wall of the cavity. The round window niche is most commonly triangular in shape

THE MEDIAL WALL:

THE MEDIAL WALL The membrane is roughly oval in shape About 2.3 x 1.9 mm in dimension and lies in a plane at right angles to the plane of the stapes footplate. It tends to curve towards the scala tympani of the basal coil of the cochlea

THE MEDIAL WALL:

THE MEDIAL WALL The Facial Nerve Canal (or Fallopian canal) runs above the promontory and oval window in an anteroposterior direction. It has a smooth rounded lateral surface that often has microdehiscences There are two or three straight blood vessels clearly visible along this line of nerve. These are the only straight blood vessels in the middle ear and indicate quite clearly that the facial nerve is very close by. The facial nerve canal is marked anteriorly by the Processus Cochleariformis , bone which houses the tendon of tensor tympani muscle.

THE MEDIAL WALL:

THE MEDIAL WALL The dome of the lateral semicircular canal is the major feature of the posterior portion of the epitympanum , lying posterior and extending a little lateral to the facial canal. During a cortical mastoidectomy , the triangular relationship of the lateral semicircular canal, the short process of the incus and the seventh nerve is often quite helpful.

THE POSTERIOR WALL:

THE POSTERIOR WALL Wider above than below In its upper part, it has a large irregular opening - the Aditus Ad Antrum ; that leads back from the posterior epitympanum into the mastoid antrum Below the aditus is a small depression, the Fossa Incudis , which houses the short process of the incus and its suspensory ligament. Below the fossa incudis and medial to the opening of the chorda tympani nerve is the pyramid, a small hollow conical projection with its apex pointing anteriorly . This houses the stapedius muscle and tendon.

THE MEDIAL WALL:

THE MEDIAL WALL The Facial Recess is a groove bounded medially by the facial nerve and laterally by the tympanic annulus, with the chorda tympani nerve running obliquely through the wall between the two

THE MEDIAL WALL:

THE MEDIAL WALL The Sinus Tympani posterior extension of the meso tympanum lies deep to both the promontory and the facial nerve. is probably the most inaccessible site in the middle ear and mastoid. can extend as far as 9 mm into the mastoid bone when measured from the tip of the pyramid. The medial wall of the sinus tympani becomes continuous with the Posterior portion of the medial wall of the tympanic cavity where it is related to the oval and round window niches and the subiculum of the promontory. Its importance is that cholesteatoma in this space is extremely difficult to eradicate

Contents of the tympanic cavity:

Contents of the tympanic cavity

Contents of the tympanic cavity:

Contents of the tympanic cavity Ossicles Malleus Incus Stapes Muscles Stapedius Tensor tympani The chorda tympani nerve The tympanic plexus

THE MALLEUS:

THE MALLEUS Largest ossicle , 9mm in length Parts Head Neck Handle Anterior process Lateral process

THE MALLEUS:

THE MALLEUS Head Lies in the epitympanum Suspended by the superior ligament Has a saddle-shaped facet on its posteromedial surface to articulate with the body of the incus by way of a synovial joint. Neck Connects the handle with the head Amputation of the head by cutting through the neck leaves both chorda tympani and tensor tympani intact

THE MALLEUS:

THE MALLEUS Handle/ manubrium The handle runs downwards, medially and slightly backwards between the mucosal and fibrous layers of the tympanic membrane. While it is very closely attached to the membrane at its lower end, there is a fine web of mucosa separating the membrane from the handle in the upper portion before it becomes adherent again at the lateral process. This can be opened surgically to create a slit without perforating the membrane to allow a prosthesis to be crimped around the malleus handle in certain types of ossicular reconstruction.

THE MALLEUS:

THE MALLEUS Lateral process Prominent landmark on the tympanic membrane Receives the anterior and posterior malleolar folds from the tympanic annulus.

THE INCUS:

THE INCUS Body Lies in the epitympanum A cartilage-covered facet corresponding to that on the malleus . Suspended by the superior incudal ligament that is attached to the tegmen tympani. Short process Projects backwards from the body to lie in the fossa incudis to which it is attached by a short suspensory ligament Long process

THE INCUS:

THE INCUS Descends into the meso tympanum behind and medial to the handle of the malleus At its tip is a small medially directed Lenticular Process. This has sometimes been called the Fourth Ossicle because of its incomplete fusion with the tip The lenticular process articulates with the head of the stapes.

THE STAPES:

THE STAPES Shaped like a stirrup Consists of a head, neck, the anterior and posterior crura and a footplate.

THE STAPES:

THE STAPES The head points laterally and has a small cartilage-covered depression for a synovial articulation with the lenticular process of the incus . The stapedius tendon inserts into the posterior part of the neck and upper portion of the posterior crus .

THE STAPES:

THE STAPES The two crura join the footplate, which usually has a convex superior margin, an almost straight inferior margin and curved anterior and posterior ends. The average dimensions of the footplate are 3 mm long and 1.4 mm wide Lies in the oval window where it is attached to the bony margins by the annular ligament.

STAPEDIUS MUSCLE:

STAPEDIUS MUSCLE Arises from the walls of the conical cavity within the pyramid. Emerges from the apex of the pyramid and inserts into the stapes. Supplied by a small branch of the facial nerve.

TENSOR TYMPANI MUSCLE:

TENSOR TYMPANI MUSCLE Long slender muscle Arising from the walls of the bony canal lying above the eustachian tube. Parts of the muscle also arise from the cartilaginous portion of the eustachian tube and the greater wing of the sphenoid. Insert into the medial aspect of the upper end of the malleus handle. Supplied from the mandibular nerve by way of a branch from the medial pterygoid nerve

CHORDA TYMPANI NERVE:

CHORDA TYMPANI NERVE This branch of the facial nerve enters the tympanic cavity from the posterior canaliculus at the junction of the lateral and posterior walls. It runs across the medial surface of the tympanic membrane between the mucosal and fibrous layers and passes medial to the upper portion of the handle of the malleus Leave by way of the anterior canaliculus , which subsequently joins the petrotympanic fissure.

TYMPANIC PLEXUS:

TYMPANIC PLEXUS Formed on the promontory by The tympanic branch of the glossopharyngeal nerve ( jacobson's nerve) Caroticotympanic nerves, arising from the sympathetic plexus around the internal carotid artery. Provide the branches to the mucous membrane lining the tympanic cavity, eustachian tube and mastoid antrum and air cells. The plexus also provides branches to join the greater superficial petrosal nerve and the lesser superficial petrosal nerve that contains all the parasympathetic fibres of the glossopharyngeal nerve.

MUCOSA OF THE TYMPANIC CAVITY:

MUCOSA OF THE TYMPANIC CAVITY Essentially mucus-secreting respiratory mucosa bearing cilia on its surface Three distinct mucociliary pathways can be identified Epitympanic Promontorial Hypotympanic - largest. Each of these pathways coalesces at the tympanic orifice of the Eustachian tube

PowerPoint Presentation:

The only route for ventilation of the epitympanic space from the mesotympanum is via two small openings between the various mucosal folds The anterior and posterior isthmus tympani. Prussak's space is found between the pars flaccida and the neck of the malleus , bounded by the lateral malleolar fold. Play an important role in the retention of keratin and subsequent development of cholesteatoma .

BLOOD SUPPLY OF THE TYMPANIC CAVITY:

BLOOD SUPPLY OF THE TYMPANIC CAVITY Arise from both the internal and external carotid system Extensive overlap Anterior tympanic A., branch of Maxillary artery and the Stylomastoid A., branch of Posterior auricular artery are the main.

EUSTACHIAN TUBE:

EUSTACHIAN TUBE Also called as Auditory tube/ Pharyngotympanic tube Connects tympanic cavity with nasopharynx 36mm long Runs downwards, forwards and medially from the middle ear at an angle of 45 degree with the horizontal

EUSTACHIAN TUBE:

EUSTACHIAN TUBE 2 parts- Posterolateral 1/3 rd is bony and Anteromedial 2/3 rd is fibrocartilaginous Junction of the two is called the Isthmus and is the narrowest part of this tube Tympanic end is in the anterior wall of the middle ear cavity Pharyngeal end opens 1.25cm behind and below the posterior part of the inferior turbinate, like a vertical slit, above which is an elevation called Torus Tubaris .

EUSTACHIAN TUBE:

EUSTACHIAN TUBE The tube is lined with respiratory mucosa containing goblet cells and mucous glands, having a carpet of ciliated epithelium on its floor. At its nasopharyngeal end, the mucosa is truly respiratory In passing along the tube towards the middle ear, the number of goblet cells and glands decreases, and the ciliary carpet becomes less profuse.

EUSTACHIAN TUBE:

EUSTACHIAN TUBE The bony portion is about 12 mm long and is widest at its oval-shaped orifice in the anterior wall of the tympanic cavity. It runs through the squamous and petrous portions of the temporal bone, gradually tapering to the isthmus, where the diameter is only 0.5 mm or less. A thin plate of bone forms the roof, separating the tube from the tensor tympani muscle above. The carotid canal lies medially and can impinge on the bony Eustachian tube. In cross section, the tube is triangular or rectangular with the horizontal diameter being the greater

EUSTACHIAN TUBE:

EUSTACHIAN TUBE The cartilaginous part of the tube is about 24 mm long Consists of a fibrocartilaginous skeleton to which is attached the peritubal muscles. At its upper border, the cartilage is bent over to resemble an inverted J, thereby forming a longer medial cartilaginous lamina and shorter lateral cartilaginous lamina. The cartilage is fixed to the base of the skull in a groove between the petrous part of the temporal bone and the greater wing of the sphenoid

EUSTACHIAN TUBE:

EUSTACHIAN TUBE Thus, the back ( posteromedial ) wall is composed of cartilage and the front ( anterolateral ) wall comprises cartilage and fibrous tissue. The apex of the cartilage is attached to the isthmus of the bony portion, while the wider medial end protrudes into the nasopharynx , lying directly under the mucosa to form the torus tubarius . In the nasopharynx , the tube opens 1-1.25 cm behind and below the posterior end of the interior turbinate. The opening is almost triangular in shape and is surrounded above and behind by the torus.

EUSTACHIAN TUBE:

EUSTACHIAN TUBE Behind the torus is the pharyngeal recess or fossa of Rosenmuller , common site of origin for nasopharyngeal carcinoma and occult primary tumors Lymphoid tissue is present around the tubal orifice and in the fossa of Rosenmuller , and may be prominent in childhood.

EUSTACHIAN TUBE:

EUSTACHIAN TUBE The bony portion is always open; the fibrocartilaginous portion is closed at rest and opens only on Swallowing Yawning forceful inflation. Ostmann fat pad Located in the inferolateral aspect of the eustachian tube Important contributing factor in closing the tube Contribute in the protection of the eustachian tube and the middle ear from retrograde flow of nasopharyngeal secretions

EUSTACHIAN TUBE:

EUSTACHIAN TUBE Muscles Help open and close the tube, thus allowing it to perform its function. These muscles are Tensor veli palatini Levator veli palatini Salpingopharyngeus

EUSTACHIAN TUBE:

EUSTACHIAN TUBE Blood vessels The arterial supply of the eustachian tube is derived from the ascending pharyngeal and middle meningeal arteries. The venous drainage is carried to the pharyngeal and pterygoid plexus of veins. The lymphatics drain into the retropharyngeal lymph nodes.

EUSTACHIAN TUBE:

EUSTACHIAN TUBE Nerve Supply Pharyngeal branch of the sphenopalatine ganglion ( vb ) for the ostium , The nervus spinosus ( vc ) for the cartilaginous portion From the tympanic plexus (IX) for the bony part.

MASTOID AIR CELL SYSTEM:

MASTOID AIR CELL SYSTEM The mastoid antrum is an air-filled sinus within the petrous part of the temporal bone. Lining of the mastoid is a flattened, non ciliated epithelium without goblet cells or mucus glands. It communicates with the middle ear by way of the aditus and has mastoid air cells arising from its walls.

MASTOID AIR CELL SYSTEM:

MASTOID AIR CELL SYSTEM The antrum , but not the air cells, is well developed at birth and by adult life has a volume of about 2 mL. The roof of the mastoid antrum and mastoid air cell space form the floor of the middle cranial fossa , while the medial wall relates to the posterior semicircular canal. More deeply and inferiorly is the dura of the posterior cranial fossa and the endolymphatic sac.

MASTOID AIR CELL SYSTEM:

MASTOID AIR CELL SYSTEM Posterior to the endolymphatic system is the sigmoid sinus The posterior belly of the digastric muscle forms a groove in the base of the mastoid bone The corresponding ridge inside the mastoid lies lateral not only to the sigmoid sinus but also to the facial nerve and is a useful landmark for finding the nerve itself

MASTOID AIR CELL SYSTEM:

MASTOID AIR CELL SYSTEM The outer wall of the mastoid lies just below the skin and is easily palpable behind the pinna . MacEwen's triangle is a direct lateral relation to the mastoid antrum and is formed by a posterior prolongation of the line of the zygomatic arch and a tangent to this that passes through the posterior border of the external auditory meatus .

DEVELOPMENT OF EAR:

DEVELOPMENT OF EAR

PowerPoint Presentation:

The first pharyngeal pouch on the inside expands due to the rapid growth of the surrounding mesenchyme and, results in the formation of the Eustachian tube, middle ear and mastoid antrum . The endoderm of the slit-like sac that is the precursor of the middle ear lies against the ectoderm of the first pharyngeal groove by the fourth week.

PowerPoint Presentation:

Mesenchyme grows in between two layers to form the middle layer of the future tympanic membrane. The underlying sac expands and as it reaches the developing ossicles and labyrinth, the epithelium is draped over these structures and their associated muscles, tendons and ligaments The future Eustachian tube lumen and middle ear spaces are formed by eight months gestation Epitympanum and mastoid antrum are developed by birth.

PowerPoint Presentation:

However, development of the mastoid air cell system does not occur until after birth, with about 90 percent of air cell formation being completed by the age of six The ossicles develop from the outer ends of the first arch ( Meckel's ) and second arch (Reichert's) cartilages that lie above and below the first pharyngeal pouch. The process begins at four weeks and adult shape, size and ossification is present by 25 weeks.

PowerPoint Presentation:

The muscles attached to the ossicles arise from the arches that give rise to that part of the ossicle to which the muscle attaches. Thus the tensor tympani is attached to the upper part of the handle of the malleus , which is derived from the first arch and is, therefore, supplied by a branch of the Vth ( mandibular ) nerve. Stapedius muscle is supplied by the VIIth (facial nerve). The chorda tympani, which is the pretrematic nerve of the second arch, supplies endodermal structures of the first arch

PowerPoint Presentation:

The external ear canal develops from The first pharyngeal groove in a complex fashion. The meatus deepens by proliferation of its ectoderm and that an anteriorly placed bud of epithelial cells expands vertically to form the skin, which will cover the future tympanic membrane. This clump of cells then opens up as a slit to form the canal lumen and produce the pars tensa and deep external canal epithelium.

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The external auricle or pinna develops from a series of small cartilaginous tubercles that surround the first pharyngeal groove. The majority of the auricle is derived from the second arch cartilages and that the tragus is the only contribution from the first arch. The rudimentary pinna has formed by 60 days although it apparently continues to grow throughout life.

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