EMB: Ear Development

Question 1

What week does the ear start to develop?

Answer 1

4

Question 2

What germ layer does the middle + external ear come from?

external: auricle (pinna), external acoustic meatus, tympanic membrane (external layer)

Middle: 3 ossicles, tympanic membrane (internal) + middle ear cavity

Answer 2

Pharyngeal arches

Question 3

What germ layer does the inner ear come from?

-vestibulocochlear organ

Answer 3

Surface Ectoderm (develops independently)

Question 4

Question 5

The auricular hillocks of the external ear are __________ cells.

Answer 5

Neural Crest

Question 6

What is the importance of the neural crest cells in the auricular hillock?

Answer 6

The neural crest cells migrate and move to form the weird looking external part of the ear.

Question 7

What is the innervation of the external ear?

Answer 7

Great Auricular N (C2 = C3) and Auriculotemporal N.

(+ a litle vagus and facial)

Question 8

What causes microtia?

Answer 8

NC cells did not migrate appropriately

Question 9

What causes Skin Tags?

Answer 9

Problem with migration of surface ectoderm + NC cells

Question 10

What does the external auditory meatus come from?

Answer 10

First pharyngeal cleft of ectoderm

Question 11

What does the Auricle come from?

Answer 11

1st and 2nd pharyngeal arches (NC)

Question 12

What fails to happen leading to no ear at all and no external auditory meatus?

Answer 12

Auricular hillocks + NC cells did not migrate/form

Question 13

What causes this?

Answer 13

Surface ectoderm cells did not undergo apoptosis, so we still have a metal plug.

Question 14

In the inner ear, how does this development work, in stages?

Answer 14

Otic placode –> Otic pit –> Otic vesicle –> membranous labyrinth

Question 15

What are the 2 parts of the membranous labyrinth?

Answer 15

Utricle (dorsal)

Saccule (ventral)

Question 16

In the membranous labyrinth, what is the utricle dependent on and its subpart the lateral canal of semicircular duct?

Answer 16

Dlx5 + Dlx6

lateral canal –> Otx1

Question 17

What components are in the Utricle part of the membranous labyrinth?

Answer 17

Semicircular ducts + utricle

Question 18

In the membranous labyrinth, the saccule part is dependent on?

Answer 18

Pax6

Question 19

What are the derivatives of the saccule part of the membranous labyrinth?

Answer 19

Cochlear duct (Pax 6) + ductus reunions + saccule + organ of corti (cochlea)

Question 20

The inner ear has hair cells that come from surface ectoderm, what are the 3 parts and function?

Answer 20

Ampullae - acceleration

Macula - gravity

Organ of Corti - sound vibration

Question 21

What nerve innervates the inner ear?

Answer 21

Vestibulocochlear

Question 22

What are the two parts of the vesitubularcochlear N. and their orgin?

Answer 22

Vestibular ganglion = SE + NC

Spiral (cochlear) ganglion = SE

Question 23

Perilymph is from the bone and surrounds the endolymph (endo = in). What does it mimic?

Answer 23

CSF

Question 24

What is endolymph similar to?

Answer 24

Intracellular fluid

Question 25

Where does perilymph come from?

Answer 25

A patent perilymphatic duct --\> allows free passage from subarachnoid space (which is why it is smilar to CSF)

Question 26

Where does endolymph come from?

Answer 26

Stria vascularis

Question 27

What protects the membranous labyrinth?

Answer 27

Bony labyrinth

Question 28

What is the bony labyrinth made of?

Answer 28

Mesenchyme (mesoderm)

Question 29

In the bony labyrith, which spaces hold perilymph?

Answer 29

Scala vestibuli + scala tympani

Question 30

What space houses the endolymph?

Answer 30

Scala media

Question 31

In the middle ear, the 1st pharyngeal cleft (ectoderm) forms \_\_\_\_\_\_\_\_\_.

Answer 31

External auditoy meatus

Question 32

In the middle ear the 1st pharyngeal pounch (endoderm) forms \_\_\_\_\_\_\_\_.

Answer 32

Tubotympanic recess

Question 33

In the middle ear, the **tympanic membrane** is formed by?

Answer 33

Everything! Ectoderm, Mesoderm, Endoderm

Question 34

In the middler ear, the ossicles (malleus + incus) are formed from?

Answer 34

NC!!! = bone Malleus = 1st arch Stapes = 2nd arch

Question 35

What nerve innervates the tensor tympani muscle of the ear?

Answer 35

CN V \*Anything innervated by 5 = 1st arch\*

Question 36

What innervates the stapedius M. of the ear?

Answer 36

CN VII

Question 37

The tensor tympani comes from the \_\_\_\_\_\_\_\_\_.

Answer 37

1st pharngeal arch mesoderm

Question 38

The stapedius M. comes from the \_\_\_\_\_\_\_\_\_.

Answer 38

2nd pharyngeal arch mesoderm

Question 39

What causes congenital deafness?

Answer 39

genetic **Maldevelopment of sound-conduction apparatus of middle + external ears (which come from pharyngeal arches).** Could be due to: first arch syndrome, mallus/incus abnormalities, stapes doesn't move, hair cells didn't form, etc. and *\*rubella infection during 7-8th week can cause defects of spiral organ and deafness\**