Bmb Week 5: Ear Embryology

Front 1

Describe the initial formation of the inner ear.

Back 1

-Composed of ectoderm near the wall of the Rhombencephalon

-Forms placode, then otic pit, then otic vesicle

-Also gives off vestibuloacoustic ganglion (in between otic vesicle and the rhombencephalon)

Front 2

What forms the vestibulo and spiral ganglia?

Back 2

Statoacoustic (vestibuloacoustic) ganglia

Front 3

What gives rise to the membranous components of the inner ear?

Back 3

Otic vesicle

Note: this is filled with endolymph

Front 4

What forms the cartilage of the ear?

Back 4

Mesenchyme

Note: also gives rise to the perilymphatic space as it vacuolizes

Front 5

What gives rise to the middle ear?

Back 5

Pharyngeal pouch, cleft, and membrane from arch 1

Adjacent mesenchyme from arch 2

Front 6

What Innervates the middle ear? Why?

Back 6

CN IX

-Due to the fact that arch 3 (CN IX) overgrows arch 2 and saddles up against arch 1 during oral cavity development

-Arch 1 (which is chiefly responsible for middle ear development) is lined by the mucosa of arch 3

Front 7

What does the first pouch form?

Back 7

-Tubotympanic recess, which develops into the following:

-Eustachian tube

-Middle ear cavity

-Mastoid air cells (occurs after birth)

Note: tympanic cavity covers the ear bones

*Surrounds them with mesoderm

Front 8

What is the eardrum composed of?

Back 8

First pharyngeal membrane:

Ectoderm, mesoderm, and endoderm

Note: endoderm comes from pharynx

Front 9

What forms the ear bones?

Back 9

Maleus and incus- cartilage of arch 1 (Meckel’s cartilage)

Stapes- cartilage of arch 2 (Reichter’s cartilage)

Front 10

What forms the tensor tympani and the stapedius muscles?

Back 10

Tensor tympani- arch 1 (CN V3)

Stapedius- arch 2 (CN VII)

Front 11

What forms the external ear?

Back 11

Hillocks from arches 1 and 2

*Each arch forms three hillocks (six total)

Front 12

What pre-natal illness can lead to congenital deafness?

Back 12

Rubella!

Front 13

What are auricular pits?

Back 13

-Cysts or fistulas that form anterior to the external ear

-Due to duplication of the first arch cleft

Note: these may or may not be attached to the actual ear

Front 14

What are auricular tags?

Back 14

Duplication of auricles

*Caused by duplication of hillocks from arches 1 and 2

Front 15

What is the meatal plug?

Back 15

Pre-natal membrane that covers the external acoustic canal

*Will go away by the time of birth (usually)

Front 16

What is anotia?

Back 16

Congenital absence of an auricle

Note: underlying structures are normal (same with microtia)