Development of pharyngeal arches

Question 1

what are the three embryonic layers of the pharyngeal arches

Answer 1

mesoderm core, ectoderm and endoderm

Question 2

what does the mesenchymal core of the arches derive from

Answer 2

mesoderm and neural crest cells

Question 3

what are the three developed layers of the pharyngeal arches

Answer 3

Mesenchymal	core	 from mesoderm and neural crest
Internal	endodermal pouch	
External cleft (ectoderm)

Question 4

what is the name for the precursor of the mouth

Answer 4

stomodeum

closed by the oropharyngeal membrane which later ruptures

Question 5

what bony structures does the first arch form

Answer 5

maxilliary prominence

mandibular prominence

Question 6

what are somitomeres

Answer 6

ill defined segments of paraxial mesoderm in the head region rostral to the somites

Question 7

what does paraxial mesoderm form

Answer 7

migrates in to the pharyngeal arches to form muscle in the head and some connective tissue

Question 8

what skeletal structures does paraxial mesoderm form

Answer 8

parietal, occipital, petrous temporal bone

Question 9

what structures does the lateral plate mesoderm form

Answer 9

laryngeal cartilage and connective tissue

Question 10

what skeletal structures does the neural crest form

Answer 10

frontal bone, sphenoid bone, squamous temporal, nasal, lamcrimal, maxilla, mandible

Question 11

what muscles does the first arch form

Answer 11

muscles of mastication, ant belly digastric, mylohyoid, tensor tympani, tensor veli palatini

Question 12

what skeletal elements does the first arch form

Answer 12

maxilla, zygomatic bone, mandible, malleus, incus

Question 13

what muscles are formed from the second arch

Answer 13

muscles of facial expression, stylohyoid, stapedius, posterior belly of digastric

Question 14

what skeletal elements are formed from the second/ hyoid arch

Answer 14

stapes, styloid process, lesser horn of the hyoid and upper body of hyoid

Question 15

what muscle is made from the third arch

Answer 15

stylopharyngeus

Question 16

what skeletal structurs are made from the third arch

Answer 16

greater horn of the hyoid, lower part of body of hyoid

Question 17

what nerve is associated with the third arch

Answer 17

glossopharyngeal

Question 18

what muscles are derived from the 4th and 6th arches

Answer 18

all the muscles of the pharynx except stylopharyngeus

all the muscles of the palate except tensor veli palatini

cricothyroid

all the muscles of the larynx `

Question 19

what skeletal structures are made from the 4th and 6th arches

Answer 19

epiglottis, laryngeal cartilages, thyroid, cuneiform , coniculate, arytenoids

Question 20

what artery does the 4th right arch give

Answer 20

subclavian artery

Question 21

what artery does the 6th arch give

Answer 21

pulmonary arteries

Question 22

Paraxial mesoderm

Answer 22

All voluntary muscles, arteries,

neurocranium, meninges, dorsal skin

Question 23

Lateral plate mesoderm

Answer 23

Laryngeal car1lages; regional connec1ve 1ssue

Question 24

what does Neural crest form

Answer 24

Pharyngeal arch skeleton,
Also viscerocranium,
glandular connective tissue,
parts of the neurocranium, teeth, interact with
ectodermal placodes for ganglia/sensory nerve forma1on

Question 25

what do Ectodermal placodes form

Answer 25

with neural crest to form neurones of sensory ganglia

(V,VII, IX and X) also sensory apparatus (eyes/nose not shown)

Question 26

what is an ectopic thymus

Answer 26

thymus remains in the neck

Question 27

what is treacher collins sydrome

Answer 27

autosomal dominant
first/ second arch

defective treacle protein
failure of apoptosis of neural crest cells and migration

abnormal eye shape
micrognathia
hearing loss
underdeveloped zygoma 
malformed ears

Question 28

what are the features of digeorge syndrome

Answer 28

3rd and 4th pouches fail to develop and thymus and parathyroids are defective

CATCH-22 
cardiac abnormality 
abnormal facies
thymic aplasia
cleft palate
hypocalcaemia 

deletion in chromosome 22- de novo

Question 29

what is the role of sonic hedghog protein in craniofacial patterning

Answer 29

governs the width of facial features

inadequate function- narrowing and fusion, cyclopia

excessive SHH widening and structures duplicated