Ear Anatomy & Tibbo

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Embryology and Anatomy of

the External EarJamie Tibbo


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General Embryology

3 Embryonic Layers: Ectoderm (Grooves) Mesoderm (Arches)

Endoderm (Pouches) 4x Grooves 5x Arches (5 th arch called 6 th arch) 4x Pouches


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General Embryology

ArchNerveArteryCartilage bar

Arch mesoderm

differentiates

MusclesBones

Vessels

Cartilage

Reference: K.J. Lee


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Overview

Development of External & Middle Ear1. External Auditory Canal2. Tympanic Membrane3. Middle Ear Cavity4. Ossicles


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Embryology of External Ear

EAC begins ( 4 th wk) Hillocks become evident

(5 th wk) Hillocks distinct ( 6 th wk)

Auricle identifiablestructures ( 8 th wk)

Auricle has adult form(18 th wk)

Meatal plug begins todisintegrate ( 20 th wk)

EAC fully open ( 28 th wk)


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Ligaments of the External Ear

Extrinsic Ligaments Anterior Ligament : attaches helix and tragus to

zygomatic process Superior Ligament : attaches spine of helix to

superior margin of bony EAC Posterior Ligament : attaches medial surface ofconcha to mastoid process

Intrinsic Ligaments

A fibrous band connects the antihelix and thecauda helicis A strong fibrous band connects the tragus to the

beginning of the helix (completing the meatusanteriorly)


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Extrinsic Muscles of the Ear

Anterior Auricular Muscle Origin : anterior part of fascia of temporal region Insertion : spine of helix Action : displaces auricle anterosuperiorly Innervation : temporal branches of CN VII

Superior Auricular Muscle Origin : fascia of temporal region Course: converges to thin, flattened tendon Insertion : upper part of cranial surface of auricle Action : displaces auricle superiorly Innervation : temporal branch of CN VII

Posterior Auricular Muscle Origin : mastoid as 2 or 3 fasciculi Insertion : cranial surface of convexity of concha Action : displaces auricle backward Innervatio n: post-auricular branch CN VII


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Intrinsic Muscles of the Ear

Rudimentary muscles extending fromone part of the auricle to another

1. Helicus Minor Muscle

2. Antitragus Muscle3. Transverse Muscle of the Auricle4. Oblique Muscle of the Auricle

5. Helicus Major Muscle


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Anatomy of the External Ear

Motor: post auricular branch of facial innervatesanterior, superior, posterior auricular muscles


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Vasculature of the Auricle

Arteries (3 main): Posterior Auricular Artery (Ext. Carotid) Anterior Auricular Artery (STA)

Occipital Artery (Mastoid Branch) Veins:

Superficial Temporal Vein Drains into Retromandibular vein

Drains into Internal Jugular

Posterior Auricular Vein Drains into External Jugular


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Innervation of the Auricle

Motor Innervation: Temporal Branch of CN VII

Anterior auricular muscle

Superior auricular muscle Post-auricular branch of CN VII

Posterior auricular muscle Intrinsic muscles of the cranial aspect of the

pinna


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Lymphatics of the External Ear


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Anatomy of the External EarExternal Auditory Canal

4 cm from tragus to TM 2.5 cm from concha to TM TM positioned obliquely

Anterior Canal & Floor 6 mm longer thanthe roof and Posterior Canal

Has an S-Shape External part directed anterosuperiorly Middle part directed posteriorly


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Anatomy of the External EarExternal Auditory Canal

Has 2 constrictions (isthmuses):1. Cartilagionous Isthmus

Narrowest segment of EAC

Located medial end of cartilagionus segmentof canal

2. Bony Isthmus Lies 2 cm from inferior aspect of concha, just

lateral to the inferior tympanic recess


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Embryology of the Middle Ear


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Embryology of Middle Ear:Tympanomastoid compartment

3rd wk tubotympanicrecess (1 st branchial pouchendoderm) approaches 1 st cleft ectoderm 6 th wk Malleus & incusidentifiable as cartilaginousmodels

5th wk

10 th wk

27 th wk


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Embryology of Middle Ear:Tympanomastoid compartment

20 th wk tympanic cavitybegins to open 22 nd wk extension toform mastoid antrum 30 th wk - malleus & incusossified 34th wk ossicles liewithin open MEC, mastoidair cells begin to develop

5th wk

10 th wk

27 th wk


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Embryology of Middle Ear: Ossicles

1st

Branchial Arch Meckels Cartilage Malleus head & neck Incus Body and Short

process Ant. Malleal ligament Sphenomandibular ligament Mandible

Mesoderm Tensor tympani muscle Masticator muscles Ant. Belly digastric Tensor palati muscle

Nerve Semilunar ganglion (CN V3)

Artery degenerates


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2nd Branchial Arch Reicherts Cartilage

Manubrium of malleus Long process of malleus Lenticular process Stapes (except

vestibular part offootplate)

Styloid process,pyramidal eminence

Stylohyoid ligament Lesser cornu of hyoid Part of body of hyoid Lower half facial canal


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2nd Branchial Arch Mesoderm:

Platysma Stapedius muscle & tendon Facial muscles Auricular muscle Posterior belly of digastric Stylohyoid muscle

Nerve:

Geniculate ganglion (CN VII) Artery:

Degenerates (stapedial artery)


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The End


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3 weeks: Developing auditory placode (ectoderm) and gut endoderm (willcontribute to inner and middle ear) Invagination into otic pit , andmigration of otocyst

7 weeks: Labyrinths are recognizable,cochlea has one turn, first sensorycells in utricle, saccule

11 weeks: CN VIII attaches, cochlea has 2 turns Adult size, active by week 21

Inner Ear Development


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Ear Anatomy & Tibbo