Pharyngeal Arches And Face Development Flashcards
Type of embryonic tissue the skull develops from
. 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
Lateral plate mesoderm forms what portion of neck?
. Laryngeal and tracheal cartilages
Head mesenchyme differentiates into ___
. 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)
Calvarium bones, primordia, and ossification pathway
. All intramembranous
. Frontal and squamous temporal from neural crest
. Squamous occipital and parietal from paraxial mesoderm
Basicranium bones, primordia, and ossification pathway
. 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
Viscerocranium bones, primordia, and ossification pathway
. 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)
Incus primordia and ossification pathway
. Neural crest form arch 1
. Endochondral
Malleus primordia and ossification pathway
. Neural crest from arch 1
. Endochondral
Stapes primordia and ossification pathway
. Neural crest from arch 2
. Endochondral
Styloid process primordia and ossification pathway
. Neural crest from arch 1
. Endochondral
Neck bones/cartilages, primordia, and ossification pathways
. Hyoid: neural crest from arch 2/3, endochondral
. Laryngeal cartilages, lat. plate mesoderm from arch 4/6, no ossification
. Cervical vertebrae: paraxial mesoderm, endochondral
Fontanelles
. 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
Cranial synchondroses
. Narrow zones of cartilage left from endochondral bones
. Slow for continued growth
. Fuse in adulthood and become immovable
Craniosynotosis
. Premature closure of 1+ cranial sutures
. Occurs in 1/2500 births
.may affect brain and facial development
Scaphoceophaly
. Early closure of sagittal suture results in long, narrow skull
Brachycephaly
. Early closure of R/L coronal sutures results in an AP short skull
Plagiocephaly
. 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
Hydrocephalus
. Buildup of CSF in ventricles of brain causes swelling of brain
. Inc. intracranial pressure can cause extreme expansion of cranial vault in newborns
Achondroplasia
. 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
Pharyngeal apparatus
. 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
Pharyngeal apparatus components
. 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
Pharyngeal arch structure
. 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.
Paraxial mesodermal arch mesenchyme gives rise to ___
. Skeletal mm. Of the face, pharynx, and larynx
Neural crest arch mesenchyme gives rise to ___
. Bones of viscerocranium and middle ear cavity
. Hyoid bone
Arch 1
. Maxillary prominence: forms midface (maxillae, lat. walls nasal cavity, zygomatic, squamous temporal bone)
. Mandibular prominence: forms mandible and inf. Portion of the face
Meckel’s cartilage
. 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
Arch 2
. 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
Arch 3
. Cartilage rod gives rise to inf. Part of hyoid bone body and greater horns
.
Arches 4/6
. Cartilages do not ossify
. Gives rise to cartilages of the larynx (thyroid, cricoid, arytenoid, corniculate, and cuneiform)
Muscle derivatives from paraxial mesoderm mesenchyme in arches
. 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
Cranial nn. Assoc. w/ each arch
1: CN V
2: CN VII
3: CN IX
4: sup. And recurrent laryngeal branches of vagus n.
Pharyngeal pouch 1
. Enlarges to form tubotympanic recess which in turn becomes the auditory tube, tympanic cavity, and mastoid antrum
Pharyngeal pouch 2
. Epithelium forms tonsillar fossa
. Palatine forms after mesoderm migrates into the fossa
Pharyngeal pouch 3
. Epithelium splits into dorsal and ventral wings
. Dorsal wing forms inf. Parathyroid glands
. Ventral wing forms the thymus
Pharyngeal pouch 4
. Epithelium forms the sup. Parathyroid gland
. Ultimobranchial body is incorporated into thyroid gland and becomes parafollicular cells that secrete calcitonin
Pharyngeal grooves
. 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
Branchial cyst
. 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
Stomodeum
. Primitive cranial opening of gut tube that appears initially as indentation in ectoderm
. Separated from developing pharynx by oropharyngeal (buccopharyngeal) membrane that then degenerates
5 mesenchymal swelling form ace development
.1 frontonasal prominence that covers developing forebrain
. 2 maxillary and 2 mandibular prominences
Sensory innervation to each prominence in developing face
. V1 to frontonasal prominence
. V2 to maxillary
. V3 to mandibular
Frontonasal prominence
. 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
Intermaxillary segment
. Gives rise to the philtrum (middle divot of upper lip), the primary palate (per axilla or ant. Hard palate), and maxillary incisor teeth
Maxillary prominences
. 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
Mandibular prominences
. Fuse together at midline to form lower jaw, lower face, and mandibular teeth
Treachery Collins Syndrome
. 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
