Transcript External ear

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
Middle ear
Internal ear
auricle
External acoustic meatus
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
crura of antihelix
•Has a lateral and medial surfaces
•The lateral surfaces presents some elevations and depressions
Triangular fossa
Helix
Antihelix
Crus of helix
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
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
Arterial supply of the auricle:
Auricularis posterior
Auricularis anterior
•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
• 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
External
acoustic meatus
Posterior malleolar fold
anterior view
Pars flaccida
Handle of malleus
Anterior malleolar fold
Layers of the tympanic membrane:
•Outer cuticular layer
•Middle fibrous layer
•Inner mucous layer
Lateral process of malleus
Cone of light
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:
Arterial 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
•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
• tympanic branch of glossopharyngeal
Inner surface of tympanic membrane is supplied by:
-Anterior tympanic (maxillary)
-Posterior tympanic (stylomastoid)
-Carotico-tympanic (internal carotid)