embryology

Question 1

Trilaminar embryo

Answer 1

endoderm and ectoderm fold sandwich of 3 tissue types:

ectoderm, mesoderm, endoderm

Question 2

Ectoderm

Answer 2

skin, hair, nails, inner ear – >

neuroectoderm: brain & sensory systems

Question 3

Mesoderm

Answer 3

muscles, connective tissue, cartilage and skeleton

Question 4

Endoderm

Answer 4

epithelial-gut and lungs, middle ear and eustachian tube

Question 5

otic placode

Answer 5

FORMS membranous labyrinth

thickening of surface ectoderm

folds in to form otic pit

separates from surface to become otocyst (internalized and surrounded by mesoderm)

Question 6

Otocyst

Answer 6

begins to elongate and form 2 regions

Utriclular Division: semicircular canals, utricle, endolymphatic duct and sac

Saccular Division: Saccule and cochlear duct

Question 7

Neural tube

Answer 7

at head=brain, spinal cord starts on outside ends up on inside by infolding of this tube/embryonic layer

Question 8

Mandibular Arch

Answer 8

first branchial arch forms middle ear canal

Question 9

Hyoid Arch

Answer 9

2nd branchial arch forms middle ear

Question 10

first branchial groove

Answer 10

between first and second branchial arches, where ear canal forms

Question 11

auricular hillocks

Answer 11

bumps on first and second branchial arches form the pinna

hillocks are ectoderm (skin) formed by cartilage underneath (mesoderm)

Question 12

greater epithelial ridge

Answer 12

inner ridge of organ of corti

develops into spiral limbus inner sulcus, inner hair cells and inner pillar cells

Question 13

lesser epithelial ridge

Answer 13

outer ridge of organ of corti

develops into outer pillar cells, deiter cells, hensen cells and OHC

~22 weeks organ of corti is called kollicker’s organ (primitive version)

Question 14

Cochlear Duct formation

Answer 14

forms by base and elongation to form spiral lamina duct

Question 15

Base Before Apex

Answer 15

Why there is more “stuff” in base than apex ex. efferent OHC

everything matures around same time, still differentiating even when fetus first responds to sound

onset of function of hearing=30 weeks

Question 16

Inner Hair Cell Development

Answer 16

both afferent and efferent contacts established around same time during development (efferent are not present in adults)

efferents withdraw and instead contact type I afferents

pruning so end up with one contact, originally much branching with many contacts

Question 17

OHC Development

Answer 17

afferents contact many OHC first

medial efferents arrive and displace some of afferents –>MORE in base than apex