Anatomy Of The Ear

Anatomy of the ear

•The organ of hearing as well as balance

Three parts • • • • •

External ear Middle ear Internal ear placed in series(?) All are located in the temporal bone

The three parts have different functions

External ear

• Auricle(pinna) and • External acoustic meatus • Auricle is made up of elastic cartilage and • Its skin is firmly attached to the cartilage and supplied by many sensory nerves(V,VII,IX,X and cervical nerves)

External acoustic meatus(25mm) • Outer cartilaginous part • Inner bony part • Extends from concha to the tympanic membrane • Lined by skin containing sebaceous glands (ceruminous glands) • Auricle to be pulled upwards,backwards and laterally to visualize the meatus and beyond

Tympanic membrane • Separates external ear from middle ear • Placed obliquely within a fibrocartilaginous ring • Its center is drawn medially by the handle of the malleus. • This inward convexity is called “umbo’

•The only structure in the body derived from all the three germ layers!!

Parts of tympanic membrane • Pars tensa • Pars flaccida • The handle of malleus is embedded in the mucous layer.

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Otoscopic view

Cone of light

Pars flaccida • Attached to the malleus are two mucosal folds • Anterior and posterior malleolar folds • Between these two folds is the pars flaccida • Chorda tympani is closely related to it

Seen from medial aspect

Applied aspects • Incisions are given in the posteroinferior quadrant • Cone of light is seen anteroinferiorly • Upper quadrants are to be avoided because of chorda tympani. • What happens if this nerve is injured?

Middle ear(tympanic cavity,tympanum) • Parts; middle ear proper(opposite the tympanic membrane) • and epitympanic recess(above the level of the tympanic membrane). • This contains the head of malleus and body of incus

Internal ear projected on the temporal bone Communications of middle ear

Boundaries of middle ear • Roof---tegmen tympani • Floor---jugular fossa • Anterior wall– has canal for tensor tympani,opening of auditory tube and carotid canal containing ICA.

Posterior wall • Presents aditus(communicating with mastoid antrum) • Canal for facial nerve • Pyramid transmitting the tendon of stapedius

Medial wall • Is the lateral aspect of internal ear • Features; • Promontory(1st turn of cochlea) • Oval window(fenestra vestibuli) • Round window(f.cochleae) • Impression made by lateral semicircular canal • Facial canal

contents • • • •

Air Ear ossicles; malleus,incus and stapes Two muscles;tensor tympani,stapedius Nerves;chorda tympani and tympanic plexus (on the promontory) • Tympanic plexus carries secretomotor fibres to the parotid gland

malleus • Has a handle(manubrium), • head and neck • Tensor tympani is inserted into the neck

incus • Has a body,long process and a short process • Long process is parallel to the handle of malleus

stapes • Has a head,two crura(anterior and posterior) • And a foot plate which closes the oval window

Articulation of ossicles

Mastoid antrum

Auditory tube • Also called pharyngo tympanic tube • Connects the nasopharynx to the anterior wall of the middle ear • Equalizes the pressure on both sides of the middle ear • Infections can spread to the middle ear and mastoid antrum from the naso pharynx.

review