Development of the Ear

Question 1

When does the ear begin to develop

Answer 1

starts at the 4th week

Question 2

What consists of the External ear

Answer 2

Consists of auricle (pinna)
ecternal acoustic meatus
external layer of tympanic membrane

Question 3

What consists of the middle ear

Answer 3

Three ossicles: malleus, incus, stapes
internal layer of tympanic membrane
middle ear cavity

Question 4

What consisits of the internal ear

Answer 4

Consists of the vestibulocochlear organ

Question 5

what does the auricle derive from and its innervation

Answer 5

Derived from the 1st and 2nd PA and neuro crest

Auricular hillocks are mesenchymal swellings covered with surface ectoderm with a neural crest component

innervated by Great auricular
Auriculotemporal (V3)
CN VII
CN X auricular branches

Question 6

what happens if a baby is born with lack or missing parts of ears (Anotia), (Microtia)

Answer 6

the Auricular hillocks did not develop
usually from abnormal Neural crest migratory

microtia= small ears
anotia= no ear

Question 7

what does the external auditory meatus arise from and what fills the hole that must dissenegrate

Answer 7

First paharyngeal cleft (groove) (surface ectoderm)

Meatal plug which will apoptosis (Surface ectoderm)

Question 8

what does the inner ear derive from

Answer 8

Derived from surface ectoderm

Question 9

What is the sequential embryologic structures of the inner ear and when does this start

Answer 9

in the 4th week

otic placode
then to otic pit
then to otic vesicle

begin to start the primordium of membranous labyrinth (surface ectoderm)

Question 10

In the Membranous labyrinth, what develops from the utricle portion of the otocyst

Answer 10

dorsal

Endolymphatic duct and sac
semicircular ducts and ampullae and lateral canal

Question 11

In the membranous labyrinth, what develops from the saccule portion of the otocyst

Answer 11

ventricle

Cochlear duct
ductus reunions
macula of saccule
organ of corti

Question 12

What is the innervation of the inner ear

Answer 12

Hair cells found in the ampulla, macula, and the organ of corti

Question 13

What does the ampulla detect

Answer 13

Rotational acceleration

Question 14

What does the macula detect

Answer 14

gravity of linear acceleration

Question 15

What does the organ of corti detect

Answer 15

Sound vibration

Question 16

What does the innervation of the inner ear

Answer 16

Cranial nerve VIII

vestibular ganglion
spiral (cochlear) ganglion

Question 17

What is perilymph and where does it come from

Answer 17

comes from the perilymphatic duct from the subarachnoid space

may also come from filtration of blood in perilymphatic space

similar in ion content to CSF

High Na, low K, and protein

Question 18

What is endolymph and where does it come from

Answer 18

Produced by the stria vascularis

similar in ion content to intracellular fluid

high K and protein, low K

Endolymphatic sac stores endolymph

Question 19

whats the clinical significance of the perilymphatic duct getting into the subarachnoid space

Answer 19

the spread of infection can travel through the perilymph in the perilymphatic duct to the subarachnoid space and this is a common way people get memningitis

Question 20

What fills the canal, and what fills the duct

Answer 20

The canal is filled with perilymph

the duct is filled with endolymph

Question 21

What embrylogical type cell makes up the organ of corti

Answer 21

surface ectoderm

arised from the cochlear duct

Question 22

What lymph is found in the scala vestibuli, sclera media

scala tympani

Answer 22

scala vestibuli = perilymph

sclera media = endolymph

scala tympani = perilymph

Question 23

what makes up the vacuoles

Answer 23

condensation of mesenchyme

semicircular ducts
scala vestibuli
scala tympani

Question 24

Where does the bony labyrinth come from

Answer 24

ossification

petrous part of temporal bone

Question 25

What forms the external auditory meatus

Answer 25

1st Pharyngeal cleft/groove (ectoderm)

Question 26

what forms the tubotympanic recess

Answer 26

1st pharyngeal pouch (endoderm)

later turns into the tympanic cavity, mastoid antrum, and the pharyngotympanic tube

Question 27

What forms the tympanic membrane

Answer 27

ectoderm, mesoderm, and endoderm

1st Pharyngeal membrane

Question 28

What makes the malleus and incus

Answer 28

1st PA which is Neural crest

Question 29

what makes the stapes

Answer 29

2nd PA which is Neural crest

Question 30

What are the ossicles covered with

Answer 30

endodermal epithelium

Question 31

What gives rise to the tensor tympani and whats this muscles action

Answer 31

the 1st pharyngeal arch mesoderm

muscle inserts on the handle of the malleus

action prevents damage from loud sounds

Question 32

What gives rise to the stapedius muscle and what is ists function

Answer 32

2nd Pharyngeal arch mesodern

inserts on neck of stapes

pulls the stapes posteriorly and tilts its base in the oval window

action prevents damage from the loud sounds

Question 33

Congenital Deafness

Answer 33

Inner ear forms independently from middle and external ears

causes: most genetic
maldevelopment of sound-conduction apparatus of middle and external ears

first arch syndrom
abnormalities of mallus or incus
congenital fixation of the stapes

Neurosensory sensory structures of inner ear

infections

• rubella during 7-8 week can cause defects to spiral organ and deafness
• cytomegalovirus-leading cause of congenital sensorineural hearing loss
• toxoplasmosis
• syphilis (toxoplasma pallidum)
• zika