Embryology

Question 1

Embryology

Answer 1

Branch of biology that deals with formation, early growth, and development of living organisms

Question 2

Embryo

Answer 2

conception to 8th week

Question 3

Fetus

Answer 3

8 weeks until 37 weeks (or after)

Question 4

Ectoderm

Answer 4

becomes nervous system, skin, and sense organs

(Inner & outer ear)–cochlea and pinna

disorders of cochlea or pinna often linked with cognitive disorders

Question 5

Mesoderm

Answer 5

skeleton, circulatory system, reproductive organs, middle ear—ossicles

Question 6

Endoderm

Answer 6

digestive and respiratory system

Question 7

First Month of Pregnancy

Answer 7

Development of CNS–dictates everything we do—

Neural plate
Neural tube
Neural crest
Notochord

Question 8

Gestational Age 3 Weeks

Answer 8

Notochord forms, neural groove (future spinal cord) forms, brain bulge at embryonic disc (becomes brain), somites (genitalia) form, primitive heart tube forms

Question 9

Gestational Age 4 Weeks

Answer 9

Heart begins to beat, branchial arches (form face and neck), NEURAL TUBE CLOSES, otic pits form (Precurser to ears), arm buds visible, first signs of lung, mouth

Question 10

Spina Bifida

Answer 10

hydrocephalus often occurs with this disorder (4th ventricle creates CSF and it builds up and pushes brain against skull so ducts that could drain CSF are either blocked or nonexistant

can have a hearing loss because brain pushes down on auditory structures or shunt may be located by VIII nerve

Question 11

Gestational Age 5 Weeks

Answer 11

Eyes, brain divides into 5 vsicles (cerebrum and cerebellum), legs and hands begin to form, “rudimentary” blood begins to move through vessels

Question 12

Gestational Age 7 Weeks

Answer 12

all organs start to form

Question 13

Gestational Age 8-10 Weeks

Answer 13

face is well formed, eyelids formed-closed and will re-open around week 28, genitals appear

Question 14

Gestational Age 25 Weeks

Answer 14

brain really starts to develop at 25 weeks, pruning occurs after birth to start to lose neurons—All the neurons that are lost are created now

cochlea is fully formed ~20 weeks=functioning inner ear

respiratory system developed enough to support gas exchange

Question 15

Toxic Susceptibility 0-2 weeks

Answer 15

Pre-organogensis so not sensitive to malformation and not connected to umbilical cord and no organs created=no problems

Question 16

Toxic susceptibility 3-8 Weeks

Answer 16

Embryonic Period

GREATEST sensitivity to environmental exposure, may not know you are pregnant, mass increases 2.5 million fold first trimester

cleft palate, neural tube defect, heart, lung, kidney, FAS

Question 17

Toxic susceptibility 9-38 weeks

Answer 17

Fetal Period

drugs and alcohol most damaging–pain medication is #1 addiction among newborn babies

functional defects, minor malformations

Question 18

Six Hillocks of His

Answer 18

GA=6-9 weeks

First Arch: tragus, crus of helix

Second Arch: ascending helix, upper helix, scaphoid & antihelix, descending helix, middle scaphoid, antihelix, antitragus

EAR LOBE DOESN’T DEVELOP FROM THIS

Question 19

External Ear

Answer 19

Tympanic Membrane:
Inner layer=endoderm
Middle layer=mesoderm
Outer layer=ectoderm

Ear reaches adult size ~9 years old, ear changes shape/size constantly through life

Question 20

Middle Ear

Answer 20

Middle ear space, tympanic cavity, ossicles

Question 21

Pharygneal Arch 1/Meckel’s cartilage

Answer 21

Because of this, common to have conductive hearing impairment –> problem with outer ear don’t be surprised to find conductive issue

Head of malleus, body & short process of incus
Tensory tympani muscle
V nerve: mandibular branch supplies tensor tympani muscle

Question 22

Pharyngeal Arch 2/Reichert’s cartilage

Answer 22

Long process of incus, handle of malleus, stapes superstructure and tympanic surface of footplate
stapedius muscle
VII nerve

Question 23

Ossification of Ossicles

Answer 23

~8.5 weeks GA incus and malleus are cartilaginous and become completed largely between weeks 15-32

stapes doesn’t start to become cartilaginous until week 15 and continues to ossify after birth

Question 24

Ossification of Ossicles and Immitance

Answer 24

middle ear space is mass-dominated because stapes is not solid bone, can prevent sound from getting through very well

cells that arose from mesoderm is gelatinous cellular mix of material unspecialized cells that remain in middle ear space of some premature babies

Question 25

Inner Ear Development

Answer 25

Otic Pit becomes otocyst ~3-4th week –> forms all structure of inner ear (cochlea + vestibular system)

day 23: invagination starts
day 30: pits close off and are closed auditory system, differentiates to endolymphatic duct without fluid there is no functioning inner ear–becomes vestibular portion of inner ear and elongates into cochlea

Question 26

Cochlea

Answer 26

weeks 8-11 cochlea forms 2.5 turns, cochlear malformation occurs early in pregnancy and VIII nerve starts to innervate

inner ear reaches adult configuration by 3rd month of pregnancy–first sense organ to develop in body

active by week 21 (But not finely tuned), becoming more mature and sophisticated through development

cochlea forms out of saccule

Question 27

Functional Hearing

Answer 27

Fetus can hear and respond to sound by 26-29 weeks (don’t hear consonants as clearly)

auditory experience promotes myelination of afferent fibers

after birth absolutely thresholds and frequency discrimination matures from high to low frequencies

frequency discrimination is adult like by 6 months postnatally & thresholds mature throughout childhood