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 Has a lateral and medial surfaces The lateral surfaces presents some elevations and depressions 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 Superior & inferior crura of antihelix Triangular fossa Helix Antihelix Crus of helix Tragus Concha Lobule Antitragus

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. 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 Auricularis posterior Auricularis superior Auricularis anterior 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 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 External acoustic meatus

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 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 Lateral process of malleus Handle of malleus Posterior malleolar fold Pars flaccida Anterior malleolar fold Lateral process of malleus Handle of malleus Cone of light External acoustic meatus Lateral view anterior view Layers of the tympanic membrane: Outer cuticular layer Middle fibrous layer Inner mucous layer

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

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) Summary of arterial & nerve supply of external ear