Pharyngeal Arches And Face Development

Question 1

Type of embryonic tissue the skull develops from

Answer 1

. Neural crest: viscerocranium plus hyoid, calvarium (ant. Cranial vault) and basicranium (ant. To sella turcica)
. Paraxial mesoderm (somitomeres and occipital somite sclerotomes): calvarium (post. Carnival vault), basicranium (post. To sella turcica), skeletal mm. Of head and neck

Question 2

Lateral plate mesoderm forms what portion of neck?

Answer 2

. Laryngeal and tracheal cartilages

Question 3

Head mesenchyme differentiates into ___

Answer 3

. Fibroblasts, chondroblasts, and osteoblasts
. Bone forms via intramembraneous ossification (cells deep to dermis differentiate directly to osteoblasts) for thin, flat bones of cranial vault and viscerocranium
. Endochondral ossification for cells that first differentiate into chondroblasts (basicranium, auditory ossicles, hyoid, cervical vertebrae)
. Some bones form via both pathways (temporal bone and occipital bone)

Question 4

Calvarium bones, primordia, and ossification pathway

Answer 4

. All intramembranous
. Frontal and squamous temporal from neural crest
. Squamous occipital and parietal from paraxial mesoderm

Question 5

Basicranium bones, primordia, and ossification pathway

Answer 5

. All endochondral
. Ethmoid and ant. 1/2 of sphenoid body and lesser wings from neural crest
. Post. 1/2 of sphenoid body, greater wings, pterygoid plates, basilar occipital, and petrous temporal are from paraxial mesoderm

Question 6

Viscerocranium bones, primordia, and ossification pathway

Answer 6

. All intramembranous
. Vomer, nasal, and inf. Nasal concha from neural crest (frontonasal prominence)
. Maxilla, lacrimal, zygomatic, and palatine from neural crest (arch 1, maxillary prominence)
. Mandible from neural crest (arch 1, mandibular prominence)

Question 7

Incus primordia and ossification pathway

Answer 7

. Neural crest form arch 1

. Endochondral

Question 8

Malleus primordia and ossification pathway

Answer 8

. Neural crest from arch 1

. Endochondral

Question 9

Stapes primordia and ossification pathway

Answer 9

. Neural crest from arch 2

. Endochondral

Question 10

Styloid process primordia and ossification pathway

Answer 10

. Neural crest from arch 1

. Endochondral

Question 11

Neck bones/cartilages, primordia, and ossification pathways

Answer 11

. Hyoid: neural crest from arch 2/3, endochondral
. Laryngeal cartilages, lat. plate mesoderm from arch 4/6, no ossification
. Cervical vertebrae: paraxial mesoderm, endochondral

Question 12

Fontanelles

Answer 12

. Bregma: ant., btw frontal and parietal bones
. Lambda: post., btw occipital and parietal bones
. Pterion: btw greater wings of sphenoid, squamous temporal, frontal and parietal bones
. Asterion: mastoid, btw parietal, occipital, and mastoid portion of temporal bone
. Close by 24 months old

Question 13

Cranial synchondroses

Answer 13

. Narrow zones of cartilage left from endochondral bones
. Slow for continued growth
. Fuse in adulthood and become immovable

Question 14

Craniosynotosis

Answer 14

. Premature closure of 1+ cranial sutures
. Occurs in 1/2500 births
.may affect brain and facial development

Question 15

Scaphoceophaly

Answer 15

. Early closure of sagittal suture results in long, narrow skull

Question 16

Brachycephaly

Answer 16

. Early closure of R/L coronal sutures results in an AP short skull

Question 17

Plagiocephaly

Answer 17

. Early closure of 1 coronal suture results in asymmetric flattening of post. Skull
. Can be positional from extended positioning of infant on flat surface resulting in asymmetric deformation of skull and early suture closure is not involved

Question 18

Hydrocephalus

Answer 18

. Buildup of CSF in ventricles of brain causes swelling of brain
. Inc. intracranial pressure can cause extreme expansion of cranial vault in newborns

Question 19

Achondroplasia

Answer 19

. Mutation in FGFR3 gene causes abnormal cartilage development
. Affects development of cartilaginous bones, esp. one bones and asicranium
. Affected individuals have shortened limbs and skull bases

Question 20

Pharyngeal apparatus

Answer 20

. In week 4
. Forms ventrally and lat. around primitive pharynx of foregut
. Forms most structures of face, nasal, and oral cavities, middle ear, pharynx, larynx, and external neck

Question 21

Pharyngeal apparatus components

Answer 21

. paired pharyngeal arches: 1-4/6
. Pharyngeal grooves: separate pharyngeal arches on outer surface of embryo, each groove lies caudal to respective arch and at same level at its corresponding pharyngeal pouch and are lined w/ ectoderm
. Pharyngeal pouches: outpouchings of inner wall of pharynx that separate adjacent arches
. Pouches are lined w/ endoderm
. Pharyngeal membranes: separate pharyngeal pouches from pharyngeal grooves, consist of external layer ectoderm, internal layer endoderm, and thin middle layer mesenchyme

Question 22

Pharyngeal arch structure

Answer 22

. Core of paraxial mesodermal arch and neural crest arch and lat. plate mesodermal mesenchyme w/ external layer of ectoderm and internal layer of endoderm
. Artery
. Cartilaginous rod
. Cranial n.

Question 23

Paraxial mesodermal arch mesenchyme gives rise to ___

Answer 23

. Skeletal mm. Of the face, pharynx, and larynx

Question 24

Neural crest arch mesenchyme gives rise to ___

Answer 24

. Bones of viscerocranium and middle ear cavity

. Hyoid bone

Question 25

Arch 1

Answer 25

. Maxillary prominence: forms midface (maxillae, lat. walls nasal cavity, zygomatic, squamous temporal bone)
. Mandibular prominence: forms mandible and inf. Portion of the face

Question 26

Meckel’s cartilage

Answer 26

. Cartilaginous rod w/in mandibular prominence
. Ventral part guides early ossification of mandible via intramembranous but cartilage itself disappears
. Middle portion of Meckel’s cartilage regresses but it’s perichondrium forms sphenomandibular ligament
. Caudal end of cartilage ossifies to form malleus and incus bones of middle ear

Question 27

Arch 2

Answer 27

. Cartilage rod gives rise to lesser horn and sup. Part of hyoid bone body
. Stylohyoid ligament
. Styloid process of temporal bone and stapes bone of middle ear

Question 28

Arch 3

Answer 28

. Cartilage rod gives rise to inf. Part of hyoid bone body and greater horns
.

Question 29

Arches 4/6

Answer 29

. Cartilages do not ossify

. Gives rise to cartilages of the larynx (thyroid, cricoid, arytenoid, corniculate, and cuneiform)

Question 30

Muscle derivatives from paraxial mesoderm mesenchyme in arches

Answer 30

. Arch 1: mm. Of mastication, ant. Digastric, mylohyoid, tensor tympani and tensor veli palatini
. Arch 2: mm. Of facial expression, post. Digastric, stapedius and stylohyoid, these mm. Migrate into arch 1 and frontonasal prominence territory and pull their motor innervation w/ them
. Arch 3: stylopharyngeus m.
. Arches 4/6: cricotyroid, levator veli palatini, palatoglossus, palatopharyngeus, intrinsic mm. Of larynx, and pharyngeal constrictors

Question 31

Cranial nn. Assoc. w/ each arch

Answer 31

1: CN V
2: CN VII
3: CN IX
4: sup. And recurrent laryngeal branches of vagus n.

Question 32

Pharyngeal pouch 1

Answer 32

. Enlarges to form tubotympanic recess which in turn becomes the auditory tube, tympanic cavity, and mastoid antrum

Question 33

Pharyngeal pouch 2

Answer 33

. Epithelium forms tonsillar fossa

. Palatine forms after mesoderm migrates into the fossa

Question 34

Pharyngeal pouch 3

Answer 34

. Epithelium splits into dorsal and ventral wings
. Dorsal wing forms inf. Parathyroid glands
. Ventral wing forms the thymus

Question 35

Pharyngeal pouch 4

Answer 35

. Epithelium forms the sup. Parathyroid gland

. Ultimobranchial body is incorporated into thyroid gland and becomes parafollicular cells that secrete calcitonin

Question 36

Pharyngeal grooves

Answer 36

. Groove 1: persists as epithelial lining of external acoustic meati and external surface of eardrums
. Grooves 2-4 overgrown by expansion of arch 2 but persist for a period of time in neck called cervical sinus
. Cervical sinus is lined w/ epithelium derived from ectoderm, sinus is normally obliterated as the neck develops

Question 37

Branchial cyst

Answer 37

. Persistent cervical sinus creates a closed sac that can swell up
. May drain onto overlying skin via external branchial fistula it into interior of pharynx
. Remnants of pharyngeal grooves 2-4 can appear in the form of cervical cysts or fistula located along the ant. Border of SCM

Question 38

Stomodeum

Answer 38

. Primitive cranial opening of gut tube that appears initially as indentation in ectoderm
. Separated from developing pharynx by oropharyngeal (buccopharyngeal) membrane that then degenerates

Question 39

5 mesenchymal swelling form ace development

Answer 39

.1 frontonasal prominence that covers developing forebrain

. 2 maxillary and 2 mandibular prominences

Question 40

Sensory innervation to each prominence in developing face

Answer 40

. V1 to frontonasal prominence
. V2 to maxillary
. V3 to mandibular

Question 41

Frontonasal prominence

Answer 41

. Forms forehead, frontal bone, bridge of nose, nasal septum, primary palate, upper incisors
. Nasal placodes (ectodermal thickenings) form on frontonasal prominence and then invaginate to become nasal pits
. Nasal pits invaginate as nasal sacs and continue to expand post. To reach developing oral cavity
. Mesenchyme bordering each nasal pit thickens to form med. and lat. nasal prominences
. Paired med. nasal prominences merge to form intermaxillary segment
. Lat. nasal prominences become alae of nose

Question 42

Intermaxillary segment

Answer 42

. Gives rise to the philtrum (middle divot of upper lip), the primary palate (per axilla or ant. Hard palate), and maxillary incisor teeth

Question 43

Maxillary prominences

Answer 43

. Form midface
. Maxillary and lat. nasal prominences initially separated by nasolacrimal groove that runs up to the area of developing eye
. Furrow invaginates, canalizes, and forms nasolacrimal duct
. Paired prominences develop palatine processes in primitive nasal/oral cavity that fuse together to form secondary hard palate

Question 44

Mandibular prominences

Answer 44

. Fuse together at midline to form lower jaw, lower face, and mandibular teeth

Question 45

Treachery Collins Syndrome

Answer 45

. Underdevelopment of arch 1 due to disruptions of neural crest cells evelopment
. People have underdeveloped zygomatic bones, mandibular hypoplasia, and malformed external ears
. Inherited as autosomal dominant but can be caused by teratogen exposure