Development of Orofacial Structures Flashcards
Describe the development of the cranium:
- develops from mesenchyme around developing brain
- neurocranium: bony case that encloses the brain
- viscerocranium: bones comprising facial skeleton
- two process (bone dependent): intramembranous ossification (mesenchyme produces osseous tissue w/o cartilage formation, endochondral ossification (bone formation occurs using a cartilaginous intermediate
- mesenchyme produces osseous fissure w/o cartilage formation
- mesenchyme condenses and becomes highly vascular
- differentiate into osteoblasts and depost osteoid > bone
- osteoblasts become trapped > form osteocytes
intramembranous ossification
- bone formation occurs in preexisting cartilaginous models (long bones)
- primary ossification centers appear in the diaphysis
- chondrocytes hypertrophy > matrix becomes calcified > cells die
endochondral ossification
Describe the development of cartilaginous neurocranium:
- several cartilages fuse, forming base of cranium (endochrondral ossification)
- defined order: occipital bone (base) > body of sphenoid > ethmoid bone
- temporal bone (petrous and mastoid parts)

Describe the development of membranous neurocranium:
- head mesenchyme at the sides and top of the brain
- will form calvaria (frontal and parietal bones) via intramembranous ossification
- interconnected via sutures

Describe the development of cartilaginous viscerocranium:
- NCC form bones and CT of craniofacial structures
- PA1: malleus and incus
- PA2: stapes, styloid process of temporal bone; lesser horn of hyoid bone
- PA3: greater horns of hyoid bone
- PA4: cartilages fuse > laryngeal cartilages

Describe the development of membranous viscerocranium:
- intramembranous ossification within maxillary prominence: squamous temporal (become part of neurocranium), maxillary, and zygomatic bones
- cells of mandibular prominence from the mandible

- premature closure of saggital suture
- cranium becomes long, narrow, and wedge shaped (50%)
scaphocephaly

- premature closure of the coronal suture
- creates a high, tower-like cranium (30%)
brachycephaly

- premature closure of the coronal suture on one side
- cranium becomes twisted and asymmetric
plagiocephaly

- premature closure of the frontal (metopic) suture
- malformation of frontal and orbital bones
trigonocephaly

Facial development depends on inductive interactions of ______, _______ _____, and ________ ____
Facial development depends on inductive interactions of forebrain, frontonasal region, and developing eye
- appear early in the 4th week of development as prominences around the stomodeum
- separated from cavity of primordial pharynx by a bilaminar membrane, the oropharyngeal membrane (ruptures at ~26 days)
facial primordia
(5: maxillary prominences (2), mandibular prominences (2), frontonasal prominence (1))

- surrounds ventrolateral part of forebrain
- frontal portion will form the forehead
- nasal portion forms rostral boundary of stomodeum and nose
- NCC from forebrain and midbrain
frontonasal prominence (FNP)

What prominences does the PA1 split to form?
- maxillary prominences (MXP): form lateral boundaries of stomodeum (midbrain and hindbrain NCC)
- mandibular prominences (MDP): form caudal boundary of stomodeum (midbrain and hindbrain NCC)

What are the first parts of the face to form?
lower jaw and lower lip
- oropharyngeal membrane disintegrates (essential for facial structures to form)
- extension and fusion of mandibular prominences toward/at the midline

- bilateral thickenings of the surface ectoderm that primordia of the nasal epithelium
- by the end of the 4th week, these structures form on inferolateral parts of the FNP
- when their edges proliferate > produce medial (MNP) and lateral nasal prominences (LNP)
nasal placodes (NP)

When the medial and lateral nasal prominences leave the nasal placodes, where do they go?
What structures do these give rise to?
- leave nasal placodes to lie in depressions, nasal pits
- pits form nostrils and nasal cavities, lateral nasal prominences form alae (side) of the nose

What does the primitive nasal sac go on to form?
What structures are closely assocated with the nasal sac?
- nasal sac will form the nasal cavity
- closely related structures: medial nasal prominence, lateral nasal prominence, nasal pit, naris (nostril)

What results in the medial nasal prominences movement toward the midline?
when maxillary prominences grow medially toward each other

What cleft separates the lateral nasal prominence from the maxillary prominence?
What process establishes continuity between side of the nose and cheek region?
- LNP separated from MXP by the nasolacrimal groove
- by end of the 6th week, each MXP merges w/ the LNP at the nasolacrimal groove which establishes continuity between the side of the nose (from LNP) and cheek region (from MXP)

When do the medial nasal prominences (MNP) merge w/ the maxillary and lateral prominences?
What does this result in?
- merge between 7-10th weeks
- results in continuity of the upper jaw and lip, and separation of nasal pits from stomodeum

- as the MNPs merge, this forms
- premaxillary part of the maxilla
- primary palate
- ‘core’ of philtrum of upper lip, while surface of lip is from MXP
intermaxillary segment

- most of the upper lip, maxilla, and secondary palate form from _______ _________
- merge laterally w/ mandibular prominences
- mesenchyme/mesoderm in PA2: forms _____ muscles, innervated by __ ___ #smileandsaycheese
- mesenchyme/mesoderm in PA1: forms muscles of ________, innervated by ___ __ #chewonthat
- most of the upper lip, maxilla, and secondary palate form from maxillary prominences
- merge laterally w/ mandibular prominences
- mesenchyme/mesoderm in PA2: forms facial muscles, innervated by CN VII #smileandsaycheese
- mesenchyme/mesoderm in PA1: forms muscles of mastication, innervated by CN V #chewonthat

Describe the development of nasal cavities:
- as the face develops, surface depressions form on the FNP, nasal placodes
- will deepen due to proliferation of facial mesenchyme
- placodes > nasal pits > primordial nasal sacs
- sacs grow dorsally and ventral to the developing forebrain
- separated from the oral cavity by oronasal membrane
- ruptures end of 6th week, connecting the cavities

Describe the formation of the primary plate:
- develops from primary and secondary palates in two stages
- begins 6th week > completed by 12th week
- critical period: end of 6th week > beginning of 9th week
- merging of the MNP forms the median palatine process, aka primary plate (wedge-shaped mass of mesenchyme, between maxillary prominences, forms premaxillary part of the maxilla

Describe the formation of the secondary palate:
- develops early in 6th week from lateral palatine processes, arises from mesenchyme of MXP
1. palatine processes extend inferiorly on each side of the tongue
2. mandible elongates > pulls tongue forward and down in the mouth
3. palatine processes ‘flip’ horizontally above the tongue (7-8 weeks)

Describe the formation of the final plate:
- completion of the fusion of primary and secondary palates
- bone gradually develops in the primary palates, forming the premaxillary part of maxilla, which houses incisors
- bone extends from maxillae and palatine bones into lateral palatine processes to form hard palate (posterior portions do not ossify > extend posteriorly and fuse > form soft palate (and uvula); palatine raphe indicates the line of fusion)
- nasopalatine canal persists in the median plane, represented in the adult hard palate by the incisive fossa
- cleft extends through upper lip
- often into the nose and/or maxilla
- lack of fusion between maxillary prominences and median nasal prominences
cleft lip

- clefts of secondary palate to incisive fossa
- may involve uvula and/or hard and soft palates
- lack of fusion between: lateral palatine processes w/ nasal septum, lateral palatine processes w/ median palatine process
cleft palate

Describe the development of the nasal septum:
- down growth from internal parts of merged medial nasal prominences
- fusion of nasal septum and palatine processes begins anteriorly (9th week) and is completed posteriorly (12th week)

Describe the process of tongue development:

- median lingual swelling (median tongue bud) appears at the end of 4th week: 1st indication of tongue development, triangular elevation in floor of primordial pharynx
- two lateral lingual swellings (distal tongue buds) develop on each side of the median lingual swelling: rapidly proliferate, merge, and overgrow median lingual swelling
- all tongue buds result from proliferation of mesenchyme in ventromedial parts of PA1
- merged lateral lingual swellings from the oral part, anterior 2/3 of the tongue
- formation of the pharyngeal part of the tongue: ventromedial parts of PA2 fuse, forming the copula; ventromedial parts of PA3 and PA4 develop the hypopharyngeal eminence
- hypopharyngeal eminence overgrows the copula, forming the posterior 1/3 of the tongue
- line of fusion of anterior and posterior parts = terminal sulcus
- tongue musculature is derived from myoblasts of occipital myotomes, accompanied by CN XII to innervate the tongue

- tongue abnormality
- incomplete fusion of lateral lingual swellings results in a bifid tongue
glossoschissis

- tongue abnormality
- frenulum is short and extends to the tip of the tongue
ankyloglossia

- tongue abnormality
- excessively large tongue caused by generalized hypertrophy, often seen in infants with Down syndrome
macroglossia

- tongue abnormality
- abnormally small tongue (rare) and usually a/w micrognathia
microglossia
PA1
- intermediate structure:
- adult structure:
- innervation:
PA1
- intermediate structure:
- median tongue bud
- lateral lingual swellings
- adult structure:
- overgrown by lateral lingual swellings
- mucosa of anterior 2/3 of tongue
- innervation:
- lingual branch (sensory) of mandibular division of trigeminal nerve (V)
- chorda tympani from facial nerve (VII; innervating arch 2) (innervates all taste buds except vallate papillae)
PA2
- intermediate structure:
- adult structure:
- innervation:
PA2
- intermediate structure: copula
- adult structure: overgrown by other structures
- innervation: N/A
PA3
- intermediate structure:
- adult structure:
- innervation:
PA3
- intermediate structure: large, ventral part of hypopharyngeal eminence
- adult structure: mucosa of most of posterior 1/3 of tongue
- innervation: sensory branch of glossopharyngeal N. (IX) (also supplies vallate papillae)
PA4
- intermediate structure:
- adult structure:
- innervation:
PA4
- intermediate structure: small, dorsal part of hypopharyngeal eminence
- adult structure: mucosa of small region on dorsal side of posterior 1/3 of tongue
- innervation: sensory fibers of superior laryngeal branch of vagus N. (X)
occipital somites
- intermediate structure:
- adult structure:
- innervation:
occipital somites
- intermediate structure: myoblasts
- adult structure: intrinsic muscles of tongue
- innervation: hypoglossal N. (XII)
head mesoderm
- intermediate structure:
- adult structure:
- innervation:
head mesoderm
- intermediate structure: myoblasts
- adult structure: palatoglossus muscle
- innervation: pharyngeal plexus of vagus N. (X)