Ear embryology

Question 1

What are placodes in embryology?

Answer 1

Specialised thickenings of the ectoderm.
Develop into complete or parts of sense organs
Are neurogenic and make PNS sensory neurons and sometimes associated receptor cells.

Question 2

What placode develops into the ear?

Answer 2

The otic placode (bilateral structure)

Question 3

What is the role of the epibranchial placodes?

Answer 3

Three placodes - the nodose, the petrosal and the geniculate
Develop into neurons
Delaminates from placodes
Forms the ganglia of cranial nerves 7,9,10.
Combines with contributions from sox-10 positive neural crest cells to develop into neuroblast (progenitor cells) to form the neuron in complete.

Question 4

What neuronal structures does the otic placode give rise to via delamination?

Answer 4

Gives rise to neurons in inner ear
Delaminate from the placode
Form the cochleovestibular ganglion of CN8 that becomes the spiral and vestibular ganglion
Combines with contributions from Sox10 positive neural crest cells to develop into neuroblasts (progenitor cells) complete neuron.

Question 5

How does the otic placode develop into the otocyst?
What structures does this give rise to?

Answer 5

Evaginates into underlying mesenchyme to form otic pit
Edges of pit come together to form a tube like structure called the otic vesicle/otocyst.
Moves deep to surface ectoderm and is surrounded by mesochyme forming otic capsule.
Occurs during week 4-5 in utero.
This forms the membranous labrythn of the inner ear.
Delamination happens from the inferomedial aspect of the tube.

Question 6

How does the otocyst develop into the inner ear?

Answer 6

Undergoes a very complex morphogenesis folding to give an elongated triangle shape then developing tubes.
Eventually folding to create conchae and vestibular system.