B7.036 Embryology of Head and Neck Structures

Question 1

components of the branchial apparatus

Answer 1

branchial clefts
branchial pouches
branchial arches

Question 2

branchial clefts

Answer 2

ectodermal ingrowths

Question 3

branchial pouches

Answer 3

endodermal outpocketings

Question 4

branchial arches

Answer 4

mesenchymal core (mesoderm and neural crest) in between the clefts and the pouches

Question 5

how are cranial neural crest cells formed

Answer 5

derived from dorsal neural ectoderm

cells delaminate by epithelial mesenchymal transition and migrate rostrally over neural tube to form branchial arches

Question 6

function of neural crest cells

Answer 6

migrate throughout the embryo and give rise to many different adult cells
give rise to majority of craniofacial structures

Question 7

first arch syndromes (neurocristopathies)

Answer 7

congenital malformations result from mutations in genes that play a role in neural crest function (induction, proliferation, EMT, migration)

Question 8

examples of first arch syndromes

Answer 8

syndromic phenotypes that include craniofacial abnormalities:

• branchiooculofacial syndrome: AP2
• campomelic dysplasia: SOX9
• mowat-wilson syndrome: ZEB2
• DiGeorge syndrome: TBX1
• treacher-collins syndrome: treacle
• saethre-chotzen syndrome: twist

Question 9

DiGeorge mnemonic

Answer 9

CATCH 22
cardiac abnormality
abnormal facies
thymic aplasia
clef palate
hypocalcemia/ hypoparathyroidism
deletion on chromosome 22

Question 10

constituents of the branchial arch

Answer 10

artery (aortic arch)
nerve (CN): V, VII, IX, X
muscle (from mesoderm)
cartilage (from neural crest)

Question 11

pharyngeal cleft

Answer 11

invagination of the ectodermal layer

Question 12

pharyngeal pouch

Answer 12

outpouching of the endodermal layer

Question 13

how are arches, clefts, and pouches arranges

Answer 13

arch is above the same numbered cleft / pouch

clefts and pouches are in line with one another

Question 14

1st and 2nd aortic arches

Answer 14

degenerate

Question 15

3rd aortic arch

Answer 15

passes through 3rd pharyngeal arch and persists as the stem of the internal carotid artery (and part of the common carotid)

Question 16

4th aortic arch

Answer 16

persists on the right as the subclavian artery

on the left becomes a portion of the arch of the aorta

Question 17

6th aortic arch

Answer 17

survives as the pulmonary arteries and ductus arteriosus

Question 18

defects in great arteries

Answer 18

usually due to persistence of arches that should have degenerated

Question 19

innervation of branchial arch 1

Answer 19

trigeminal CN V

Question 20

innervation of branchial arch 2

Answer 20

facial CN VII

Question 21

innervation of branchial arch 3

Answer 21

glossopharyngeal CN IX

Question 22

innervation of branchial arches 4-6

Answer 22

vagus CN X

Question 23

first arch muscles

Answer 23

mastication
-temporalis
-masseter
anterior belly of digastric

Question 24

second arch muscles

Answer 24

facial expression

posterior belly of digastric

Question 25

third arch muscles

Answer 25

stylopharyngeus

Question 26

fourth-sixth arch muscles

Answer 26

pharyngeal and laryngeal muscles

Question 27

first arch cartilage

Answer 27

Meckel's cartilage (lower jaw) malleus incus

Question 28

second arch cartilage

Answer 28

stapes styloid process stylohyoid ligament top half of hyoid bone

Question 29

third arch cartilage

Answer 29

bottom half of hyoid bone | greater horn of hyoid bone

Question 30

fourth arch cartilage

Answer 30

thyroid cartilage | cricoid cartilage

Question 31

structure of pharyngeal pouch derivatives at 5-6 weeks​

Answer 31

2nd arch begins to grow over others 2-4th clefts merge together 3rd and 4th pouches grow 2 processes

Question 32

structure of pharyngeal pouch derivatives at 6 weeks

Answer 32

``` 2nd arch covers all pouches 2-4th clefts are now the cervical sinus 1st cleft = external auditory meatus 1st pouch = auditory tube 2nd pouch = palatine tonsil 3rd pouch = inferior parathyroid, thymus 4th pouch = superior parathyroud ```

Question 33

structure of pharyngeal pouch derivatives at 6-8th weeks

Answer 33

thyroid gland descends from foramen cecum superior parathyroid descends onto thyroid from 4th pouch inferior parathyroid descends further than superior to bottom of thyroid from 3rd pouch thymus descends from 3rd pouch

Question 34

BC1 summary

Answer 34

inward growth | external auditory meatus

Question 35

BC 2,3,4 summary

Answer 35

BA2 grows over | cervical sinus

Question 36

BP1 summary

Answer 36

grows toward BC 1 | tympanic cavity + auditory tube

Question 37

BP2 summary

Answer 37

1 outpocket | palatine tonsil

Question 38

BP3 summary

Answer 38

2 outpockets | inferior parathyroid + thymus

Question 39

BP4 summary

Answer 39

2 outpockets | superior parathyroid + ultimobranchial body

Question 40

issues with the cervical sinus

Answer 40

potential for lateral fistulas and cysts | next to SCM muscle

Question 41

formation of thyroid

Answer 41

midline structure | gland descends from foramen cecum to sit in the ventral cervical region below the hyoid bone

Question 42

issues with thyroid formation

Answer 42

potential for midline cysts along path

Question 43

embryonic origin of the tongue

Answer 43

lateral swellings within BA1 and BA3 grow together anterior 2/3 = BA1 posterior 1/3 = BA3 epiglottis = BA4-6 BA2 disappears and is not a part of the tongue

Question 44

general sensory innervation of the tongue

Answer 44

anterior 2/3: mandibular branch of V posterior 1/3 = glossopharyngeal IX extreme posterior / epiglottis = Xth nerve

Question 45

taste innervation of the tongue

Answer 45

anterior 2/3: chorda tympani (branch of VII) posterior 1/3 = glossopharyngeal IX extreme posterior / epiglottis = Xth nerve

Question 46

intrinsic motor innervation of tongue

Answer 46

intrinsic musculature: hypoglossal (XII) | palatoglossus: Xth nerve

Question 47

prevalence of atypical clefts

Answer 47

very rare | 0.25% of all clefts

Question 48

most common type of cleft deformity

Answer 48

isolated cleft lip cleft lip & palate isolated cleft palate

Question 49

epidemiology of cleft lip/palate

Answer 49

30% syndromic 70% non-syndromic (isolated) -CLO and CL/P 1/1000 (males 80%) -CPO 1/2500 (females 67%)

Question 50

inheritance of cleft lip/palate

Answer 50

classic complex trait with genetic and environmental factors | 40-60% concordance in MZ twins

Question 51

common, complex disorders of the newborn

Answer 51

cleft lip and palate (1 in 700) congenital heart disease (1 in 200) neural tube defects (1 in 1000) preterm birth (1 in 8)

Question 52

initial development of the face

Answer 52

BA1 splits into maxillary and mandibular processes by 5th week nasal pits form

Question 53

fusion of the facial prominences

Answer 53

lateral and medial nasal prominences form on the side of the nasal pits maxillary prominence fuses with medial nasal prominence (this goes wrong in a cleft lip)

Question 54

frontonasal prominence structures

Answer 54

forehead bridge of nose medial and lateral nasal prominences

Question 55

maxillary prominence structures

Answer 55

cheeks | lateral portion of upper lip

Question 56

medial nasal prominence structures

Answer 56

philtrum of upper lip crest tip of nose

Question 57

lateral nasal prominence structures

Answer 57

alae of nose

Question 58

mandibular prominence structures

Answer 58

lower lip

Question 59

2 segments of the palate

Answer 59

primary palate- medial nasal process | secondary palate- inward extensions of maxillary process

Question 60

growth of palatine shelves

Answer 60

1. initial vertical growth 2. elevation of shelves above the tongue, tongue depresses 3. inward growth and fusion of palatal shelves (forming secondary palate)

Question 61

pierre robin sequence

Answer 61

mandible most severely affected (micrognathia) shortened jaw causes glossoptosis (posteriorly placed tongue) which causes formation of a cleft palate 1/8500 births