Ear development

Question 1

Critical period for ear development

Answer 1

Week 4-8

Question 2

External ear:

Answer 2

Auricle, external acoustic meatus, external tympanic membrane

Question 3

Middle ear:

Answer 3

Three ossicles, internal tympanic and middle ear cavity

Question 4

Internal ear:

Answer 4

Vestibulocochlear organs

Question 5

Auricle development:

Which pharyngeal arch?

Answer 5

PA 1 and 2 
Auricular hillocks  (neural crest) are mesenchymal swelling covered with surface ectoderm > migrate and give the ear its shape

Question 6

nnervation of the external ear:

Answer 6

Great Auricular
V3 - Auriculotemporal (PA 1)
CN VII (PA 2)
CN X (auricular branches)

Question 7

Abnormal auricle shape:

Answer 7

Cartilage present = Hillocks did not migrate properly

Skin only - surface ectoderm did not migrate properly

Question 8

Anotia

Microtia

Answer 8

• No ear. No hillocks. Neural crest did not migrate.

- Small ears. Abnormal hillock and neural crest migration

Question 9

Development of the external auditory meatus:

Which part of the pharyngeal arches?

Answer 9

Derived from first pharyngeal cleft
1st pharyngeal cleft (surface ectoderm) and tubotympanic recess (1st arch pouch) forms the middle ear
Cleft meets the pouch > surface ectoderm proliferates > meatal plus (external auditory meatus) forms and fills up with these cells > the meatal plug will undergo apoptosis and form the shape of the outer ear

Question 10

Inner ear development:
Derived from?
Forms when?

Answer 10

Derived from ectoderm, first one to form at week 4
Surface ectoderm thickens and forms the otic placode > this invaginates and forms the otic pit > rounds up to see the vesicle which will migrate into the head
-These structures give rise to the primordium of membranous labyrinth

Question 11

Draw the developmental process of the inner ear:

Answer 11

Refer to drawings

Question 12

Draw the development of the membranous labyrinth of the inner ear:

Answer 12

Refer to drawings

Question 13

Membranous labyrinth is derived from:

Answer 13

Surface ectoderm

Question 14

Structures developing from the utricle (dorsal):

Answer 14

Endolymphatic sac and duct
Semicircular ducts and ampullae, lateral canal
Macula of utricle

Question 15

Structures developing from the saccule (ventral):

Answer 15

Cochlear duct, ductus reunions, macula of saccule, organ of corti

Question 16

What do these hair cells detect?
Ampullae
Macula
Organ of corti

Answer 16

• rotational acceleration
• gravity and linear acceleration
• sound vibration

All come from surface ectoderm

Question 17

What innervates the inner ear ?

Answer 17

Cranial nerve VIII (surface ectoderm, specifically the otic placode)
Forms the vestibular ganglion which forms the Vestibular N. and the spiral (cochlear ganglion) which forms the Cochlear N.

Question 18

Perilymph:

Answer 18

Drainage: passes through the perilymphatic duct from subarachnoid space into inner ear
Similar in ion content to CSF (high Na, low K and protein
Separates the endolymph from the bony labyrinth
Derived from mesoderm

Question 19

Endolymph:

Answer 19

Produced by stria vascularis
Similar ion content to intracellular fluid (High K and protein, low Na)
Stored by endolymphatic sac
Fills the structures of the membranous labyrinth

Question 20

Perilymph and subarachnoid space

Answer 20

Perilymph drains to the subarachnoid space. Inner ear infections can get into the perilymph and drain to the subarachnoid space (meningitis

Question 21

Development of the bony labyrinth of the inner ear:

Answer 21

Formed by the condensation of mesenchyme (mesoderm) > ossifies and forms the petrous part of the temporal bone

Question 22

Scala vestibuli and scala tympani are filled with …

Scala Media is filled with…

Answer 22

Perilymph

Endolymph

Question 23

Draw the development of the bony labyrinth

Answer 23

Refer to drawings

Question 24

Middle ear development: 
External auditory meatus 
Tubotympanic recess
Tympanic membrane
Malleus and Incus
Stapes
Ossicles

Answer 24

1st pharyngeal cleft (ectoderm)
1st pharyngeal pouch (endoderm)
1st arch Ectoderm (external layer), 1st arch mesoderm and 1st arch endoderm
1st arch neural crest
2nd arch neural crest
Derived from neural crest, but are covered with endodermal epithelium

Question 25

Draw the development of the middle ear

Answer 25

Refer to drawings

Question 26

What cell type are these muscles from?
Tensor Tympani
Stapedius

Answer 26

1st arch mesoderm (innervated by V3)

2nd arch mesoderm (innervated by CN VII)

Question 27

Congenital deafness:

Answer 27

Cause: Genetic. Maldevelopment of sound conduction apparatus of middle and external ear. First arch syndrome, abnormalities of malleus and incus, congenital fixation of the stapes
-Neurosensory deafness (for inner ear derived problems)

Question 28

Rubella infection

Cytomegalovirus

Answer 28

• Infection during 7-8th week can cause defects in the spiral organ and deafness
• leading cause of congenital sensorineural hearing loss

Question 29

Cytomegalovirus infection causes….
Herpes simplex virus causes….
Human parovirus B19 causes …

Answer 29

Sensorineural hearing loss
Hemolytic anemia
Fetal anemia

Question 30

Rubella causes ….
Toxoplasma gondii causes …
Treponema pallidum causes …

Answer 30

Cardiac abnormalities, sensorineural deafness, cataract, micropthalmos, glaucoma, pigmented retinopathy, neonate bleeding

• microphthalmia, hearing loss
• congenital deafness

Question 31

Venezuelan equine encephalitis virus causes…

Varicella virus causes…

Answer 31

• microphthalmia

- cataracts, microphthalmia, optic atrophy