Embryologic Development of the Auditory System Flashcards Preview

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Flashcards in Embryologic Development of the Auditory System Deck (9)
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1
Q

Embryologic Development of the Auditory System: General terminology

A
  • Gestation: 40 wks
  • Premature birth: before 37th week
    1. Pre-embryonic stage: fert. until 3 wks
    2. Embryonic stage: 4-8 weeks ( brachial arches emerge and 3 germ layers differentiate → major features of ear arises)
    3. Fetal stage: 9 wks-term
  • After fertiliz. → Zygotes (Mitosis → cells divide) → Blastocyst: very early mass of cells implanted in the uterus then dev. into embryo
  • Placenta
2
Q

Three germ layers

A
  1. Ectoderm: cochlea
  2. Mesoderm: outer and middle ear
  3. Endoderm: epithelial lining of Eustachian tube, middle ear cavity
3
Q

Pharyngeal arches (AKA branchial arches)?

A
  • 4 pairs of branchial arches made of all 3 germ layers
  • Pharyngeal groove (ecto. - separate arches externally)
  • Pharyngeal pouch (endo - separate arches internally)
  • 1st/2nd arch becomes outer/middle ear
  • 1st branchial groove forms permanent structure (ear canal)
4
Q

Embryologic origins of outer ear?

A
  • Pinna: 1st and 2nd branchial arc; auricular hillocks form and fuse into external ear
  • EAM: 1st branchial groove (ectoderm) deepens into ear canal
  • TM: 1st branchial groove (ectoderm) and pouch (endoderm)
5
Q

Embryologic origins of middle ear?

A

Mandibular arch/1st branchial arch
- malleus and incus

1st pharyngeal pouch (endo)

 - mid ear cavity
 - eustachian tube 

Hyoid arch/2nd branchial arch

 - stapes
 - stapedius stylohyoid
6
Q

Embryologic origins of inner ear?

A

Otic Placodes (sink into mesoderm) → Otic Pits → otocyst (AKA otic vesicle) → inner ear:

 - Cochlea
 - Semicircular canals
 - Saccule and utricle * ***inner ear sensory system  is from ectoderm**** - Rapid dev btwn 4th - 12th wk
7
Q

Embryologic origins of CN VIII?

A

4th wk: CN VIII originates from otic placode and neural crest
5th wk: Nerve fibers contact wall of otocyst from vestibular ganglion
7th wk: vest. ganglion forms nerve trunks (innervate semi canals and utricule/saccule)
11/12th wk: efferent fibers contact IHC

8
Q

Define teratogen

A

Drugs, infections, or toxins that cause birth defects

9
Q

Teratogens: effect on aud dev.

A

During periods of rapid tissue differentiation (3-8 wks), exposure to teratogens = severe congenital anomalies

  • concentration and maternal interaction also affect teratogenicity
  • genetics of embryo influence if teratogen affects its dev.