External ear

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ANATOMY OF THE EAR

•The organ of hearing and equilibrium

•Divided into three parts:

External ear

• Middle ear

Internal ear

External ear

Includes:

The Auricle and;

• The External acoustic meatus auricle

External acoustic meatus

Middle ear

Internal ear

External ear

External Ear

Auricle

Collects sound waves and directs them into the external acoustic meatus

•Formed of a thin plate of cartilage covered by skin

Superior & inferior

•Has a lateral and medial surfaces

•The lateral surfaces presents some elevations and depressions crura of antihelix

Helix

Antihelix

Parts of the auricle

:

Helix : the curved margin of the auricle

•Begins anteriorly at a ridge called the crus of helix

•Ends postero-inferiorly at the lobule of the ear

Antihelix : a cruved ridge in front of the post. part of helix

•Superiorly it divides into sup. & inf. crura

•The crura are separated by a the triangular fossa

Scaphoid fossa : depression between helix and antihelix

Tragus : a projection below the crus of helix

Antitragus : a small tubercle on the lower part of antihelix

Concha : the central depression of the auricle

Concha

Antitragus

Lobule

Triangular fossa

Crus of helix

Tragus

Muscles of the auricle:

Extrinsic muscles:

•Auricularis anterior

Supplied by temporal branches of facial n .

•Auricularis superior

•Auricularis posterior , supplied by post auricular n. (from facial)

Intrinsic muscles : slips of striated muscles fibers, supplied by temporal and posterior auricular branches of facial n .

Auricularis superior

Auricularis posterior

Auricularis anterior

Arterial supply of the auricle:

•Auricular branches of superficial temporal a .

•Auricular branch of posterior auricular a .

•Auricular branch of occipital a .

Sensory nerve supply of the auricle:

Great auricular : supplies lower 1/3 of lateral surface & lower 2/3 of medial surface

Auriculotemporal : supplies upper 2/3 of lateral surface

Lesser occipital : supplies upper 1/3 of medial surface

Auricular branch of vagus : supplies skin of concha

Facial nerve : supplies skin of concha via a communication with the auricular branch of vagus

External acoustic meatus

External acoustic meatus

•The passage between the concha and the outer surface of tympanic membrane

Conducts sound waves from the auricle to the tympanic membrane

Measures 4 cm from the tragus (2.5 cm from bottom of concha)

•The lateral 1/3 forms the cartilagenous part of the meatus

•The medial 2/3 form the bony part of the meatus

•The anterior wall and floor of the meatus are longer than the roof and post wall

(because of the obliquity of the tympanic membrane)

•The meatus is

S-shaped and has 2 constrictions :

•At the junction between the cartilagenous and bony parts

•In the bony part (5mm from the tympanic membrane) called the isthmus

External acoustic meatus

•The skin of the meatus is thin and firmly attached to its walls

•The outer 1/3 contains hairs and seruminous glands (secrete wax )

Tympanic membrane

Tympanic Membrane

•An oval semitransparent membrane

•Obliquely situated at the bottom of the external acoustic meatus

•The circumference of the membrane is thick and fitted into the tympanic sulcus of temporal bone

•The upper part of the sulcus is deficient forming a notch

•Two fibrous bands connect the sides of the notch to the lateral process of malleus( anterior & posterior malleolar folds )

•Three parts of the membrane can be recognized:

Pars flaccida : the triangular area between the malleolar folds

Pars tensa : the greater part of the membrane

Cone of light : at the antero-inferior part of the membrane

Lateral process of malleus

Handle of malleus

External acoustic meatus

• The handle of malleus is attched to the center of the inner surface of the membrane leading to projection of the membrane towards the middle ear

• The membrane is concave laterally and convex medially

Posterior malleolar fold

Pars flaccida

Handle of malleus

anterior view

Anterior malleolar fold

Layers of the tympanic membrane:

Outer cuticular layer

Middle fibrous layer

Inner mucous layer

Cone of light

Lateral process of malleus

Lateral view

Arterial supply of the external acoustic meatus

:

•Auricular branches of superficial temporal

•Auricular branch of posterior auricular

Deep auricular (branch of maxillary)

Arterial supply of the tympanic membrane :

Outer surface :

Deep auricular (branch of maxillary)

Inner surface :

Anterior tympanic (maxillary)

Posterior tympanic (stylomastoid artery)

Carotico-tympanic (internal carotid artery)

Nerve supply of the external acoustic meatus:

•Auriculotemporal n: supplies anterior wall and roof

•Auricular branch of vagus: supplies floor and posterior wall

Nerve supply of the tympanic membrane:

Outer surface : same nerves which supply the external meatus

Inner surface : tympanic branch of glossopharyngeal

Summary of arterial & nerve supply of external ear

Nerve supply of the external ear:

Auriculotemporal n:

-upper 2/3 of lateral wall of auricle

-anterior wall and roof of meatus

-outer surface of tympanic membrane

Auricular branch of vagus:

-concha of auricle

-floor and posterior wall of meatus

-outer surface of tympanic membrane

Great auricular n:

-lower 1/3 of lateral surface of auricle

-lower 2/3 of medial surface of auricle

Lesser occipital n:

-upper 1/3 of medial surface of auricle

Inner surface of tympanic membrane is supplied by

• tympanic branch of glossopharyngeal

Arterial supply of the external ear:

•Auricular branches of superficial temporal a .

-lateral surface of auricle

-external acoustic meatus

•Auricular branch of posterior auricular a .

-medial surface of auricle

-external acoustic meatus

Deep auricular (of maxillary)

-outer surface of tympanic membrane

Inner surface of tympanic membrane is supplied by:

Anterior tympanic (maxillary)

Posterior tympanic (stylomastoid)

Carotico -tympanic (internal carotid)

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