Development of Orofacial Structures Flashcards
1
Q
Describe the development of the cranium:
A
- 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
2
Q
- 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
A
intramembranous ossification
3
Q
- bone formation occurs in preexisting cartilaginous models (long bones)
- primary ossification centers appear in the diaphysis
- chondrocytes hypertrophy > matrix becomes calcified > cells die
A
endochondral ossification
4
Q
Describe the development of cartilaginous neurocranium:
A
- 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)
5
Q
Describe the development of membranous neurocranium:
A
- head mesenchyme at the sides and top of the brain
- will form calvaria (frontal and parietal bones) via intramembranous ossification
- interconnected via sutures
6
Q
Describe the development of cartilaginous viscerocranium:
A
- 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
7
Q
Describe the development of membranous viscerocranium:
A
- intramembranous ossification within maxillary prominence: squamous temporal (become part of neurocranium), maxillary, and zygomatic bones
- cells of mandibular prominence from the mandible
8
Q
- premature closure of saggital suture
- cranium becomes long, narrow, and wedge shaped (50%)
A
scaphocephaly
9
Q
- premature closure of the coronal suture
- creates a high, tower-like cranium (30%)
A
brachycephaly
10
Q
- premature closure of the coronal suture on one side
- cranium becomes twisted and asymmetric
A
plagiocephaly
11
Q
- premature closure of the frontal (metopic) suture
- malformation of frontal and orbital bones
A
trigonocephaly
12
Q
Facial development depends on inductive interactions of ______, _______ _____, and ________ ____
A
Facial development depends on inductive interactions of forebrain, frontonasal region, and developing eye
13
Q
- 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)
A
facial primordia
(5: maxillary prominences (2), mandibular prominences (2), frontonasal prominence (1))
14
Q
- 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
A
frontonasal prominence (FNP)
15
Q
What prominences does the PA1 split to form?
A
- maxillary prominences (MXP): form lateral boundaries of stomodeum (midbrain and hindbrain NCC)
- mandibular prominences (MDP): form caudal boundary of stomodeum (midbrain and hindbrain NCC)
16
Q
What are the first parts of the face to form?
A
lower jaw and lower lip
- oropharyngeal membrane disintegrates (essential for facial structures to form)
- extension and fusion of mandibular prominences toward/at the midline
17
Q
- 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)
A
nasal placodes (NP)
18
Q
When the medial and lateral nasal prominences leave the nasal placodes, where do they go?
What structures do these give rise to?
A
- leave nasal placodes to lie in depressions, nasal pits
- pits form nostrils and nasal cavities, lateral nasal prominences form alae (side) of the nose
19
Q
What does the primitive nasal sac go on to form?
What structures are closely assocated with the nasal sac?
A
- nasal sac will form the nasal cavity
- closely related structures: medial nasal prominence, lateral nasal prominence, nasal pit, naris (nostril)
20
Q
What results in the medial nasal prominences movement toward the midline?
A
when maxillary prominences grow medially toward each other
21
Q
What cleft separates the lateral nasal prominence from the maxillary prominence?
What process establishes continuity between side of the nose and cheek region?
A
- 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)
22
Q
When do the medial nasal prominences (MNP) merge w/ the maxillary and lateral prominences?
What does this result in?
A
- merge between 7-10th weeks
- results in continuity of the upper jaw and lip, and separation of nasal pits from stomodeum
23
Q
- 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
A
intermaxillary segment
24
Q
- 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
A
- 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
25
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
26
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**
27
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)
28
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**
29
- cleft extends through upper lip
- often into the nose and/or maxilla
- lack of fusion between maxillary prominences and median nasal prominences
cleft lip
30
- 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
31
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)
32
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
33
- tongue abnormality
- incomplete fusion of lateral lingual swellings results in a bifid tongue
glossoschissis
34
- tongue abnormality
- frenulum is short and extends to the tip of the tongue
ankyloglossia
35
- tongue abnormality
- excessively large tongue caused by generalized hypertrophy, often seen in infants with Down syndrome
macroglossia
36
- tongue abnormality
- abnormally small tongue (rare) and usually a/w micrognathia
microglossia
37
PA1
- intermediate structure:
- adult structure:
- innervation:
PA1
- intermediate structure:
1. median tongue bud
2. lateral lingual swellings
- adult structure:
1. overgrown by lateral lingual swellings
2. mucosa of anterior 2/3 of tongue
- innervation:
1. lingual branch (sensory) of mandibular division of trigeminal nerve (V)
2. chorda tympani from facial nerve (VII; innervating arch 2) (innervates all taste buds except vallate papillae)
38
PA2
- intermediate structure:
- adult structure:
- innervation:
PA2
- intermediate structure: copula
- adult structure: overgrown by other structures
- innervation: N/A
39
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)
40
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)
41
occipital somites
- intermediate structure:
- adult structure:
- innervation:
occipital somites
- intermediate structure: myoblasts
- adult structure: intrinsic muscles of tongue
- innervation: hypoglossal N. (XII)
42
head mesoderm
- intermediate structure:
- adult structure:
- innervation:
head mesoderm
- intermediate structure: myoblasts
- adult structure: palatoglossus muscle
- innervation: pharyngeal plexus of vagus N. (X)
