Ear Development

Question 1

Auricle derivation

Answer 1

Derived from 1st/2nd PAs

Auricular hillocks are mesenchymal swellings covered with ectoderm- neural crest component

Question 2

Innervation to auricle

Answer 2

Great auricular nerve
CN V3 auriculotemporal
CN VII
CN X

Question 3

External auditory meatus derived from

Answer 3

First pharyngeal groove

Meatal plug formed originally and then disappears

Question 4

Inner ear derived from

Answer 4

Ectoderm

Otic placode–> otic pit–> otic vesicle

Question 5

Utricle

Answer 5

Dorsal
Endolymphatic duct and sac
Semicircular ducts and ampullae
Macula of utricle

Question 6

Saccule

Answer 6

Ventral
Cochlear duct
Ductus reunions
Macula of saccule, organ of corti

Question 7

Function of ampullae, macula and organ of corti

Answer 7

Ampullae- sense acceleration
Macule- sense gravity
Organ of corti- sound vibration

Question 8

Perilymph

Answer 8

Perilymphatic duct usually patent- free passage from subarachnoid space into inner ear
May also come from filtration of blood in perilymphatic space
Similar ion content to CSF- high Na, low K and protein

Question 9

Endolymph

Answer 9

Stria vascularis appears to produce endolymph
Similar in content to intracellular fluid- High K and protein, low Na
Endolymphatic sac stores endolymph

Question 10

Bony labrynth

Answer 10

Condensation of mesenchyme

Vacuoles with perilymphatic space (semicircular ducts), scala vestibuli, scala tympani