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Development Of Orofacial Structures Flashcards

1
Q

What does the cranium develop from?

A

Mesenchyme around the developing brain

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2
Q

What is the neurocranium?

A

A bony case that encloses the brain

Two types: Cartilaginous and membranous

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3
Q

What is the viscerocranium?

A

Bones comprising the facial skeleton

Also has a cartilaginous and membranous type

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4
Q

What are the two processes involved with development of the cranium?

A

Intramembranous and endochondral ossification

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5
Q

What is intramembranous ossification?

A

Mesenchyme produces osseous tissue w/o cartilage formation
Mesenchyme condenses and becomes highly vascular
Differentiate into osteoblasts and deposit osteoid -> bone
Osteoblasts become trapped and form osteocytes

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6
Q

What is endochondral ossification?

A

Bone formation occurs using a pre-existing cartilaginous intermediate (long bones)
Primary ossification centers appear in the diaphysis
Chondrocytes hypertrophy -> matrix becomes calcified -> cells die

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7
Q

Describe the cartilaginous neurocranium

A 
Several cartilages fuse, forming base of cranium (endochondral ossification)
Defined order: occipital bone (base) -> body of sphenoid -> ethmoid bone 
Temporal bone (petrous and mastoid parts)
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8
Q

Describe the 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

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9
Q

Describe the cartilaginous viscerocranium

A

NCCs form bones and Ct of craniofacial structures

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10
Q

Describe the membranous viscerocranium

A

Intramembranous ossification within maxillary prominence: squamous temporal (which will become part of the neurocranium), maxillary and zygomatic bones
Cells of mandibular prominence form the mandible

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11
Q

What are examples of craniosynostosis?

A

Scaphocephaly, brachiocephaly, plagiocephaly, trigonocephaly

Premature closure of a suture

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12
Q

What is scaphocephaly?

A

Premature closure of sagittal suture -> cranium becomes long, narrow and wedge shaped (50%)

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13
Q

What is brachycephaly?

A

Premature closure of the coronal suture -> a high, tower like cranium (30%)

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14
Q

What is plagiocephaly?

A

Premature closure of the coronal (anterior plagiocephaly) or lambdoid (posterior) suture on one side -> cranium is twisted and asymmetrical

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15
Q

What is trigonocephaly?

A

Premature closure of the frontal (metopic) suture -> malformation of frontal and orbital bones

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16
Q

What does facial development depend on?

A

Inductive interactions of forebrain, frontonasal region and developing eye

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17
Q

Describe facial primordia

A

Five facial primordia appear early in week 4 as prominences around the stomodeum
Separated from cavity of primordial pharynx by a bilaminar membrane known as the oropharyngeal membrane that ruptures at ~26 days

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18
Q

What are the different facial prominences?

A

Maxillary (2), mandibular (2) and frontonasal (1) prominence

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19
Q

When does facial development occur?

A

During weeks 4-8

Mesenchyme contains active growth centers

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20
Q

Describe the frontonasal prominence (FNP)

A

Surrounds ventrolateral part of the forebrain
Frontal portion forms forehead
Nasal portion forms rostral boundary of stomodeum and nose
NCC from forebrain and midbrain

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21
Q

Where do the maxillary and mandibular prominences split from?

A

PA1

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22
Q

What does the maxillary prominences (MXP) form?

A

Lateral boundaries of stomodeum

Midbrain and hindbrain NCC

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23
Q

What do the mandibular prominences (MDP) form?

A

Caudal boundary of stomodeum

Midbrain and hindbrain NCC

24
Q

Which parts of the face are the first parts to form?

A

Lower jaw and lower lip
Occurs after the oropharyngeal membrane disintegrates
Involves extension and fusion of mandibular prominences toward/at the midline

25
What occurs by the end of week 4?
Nasal placodes form on inferolateral parts of the FNP | Bilateral oval thickenings of the surface ectoderm that are primordia of the nasal epithelium
26
What occurs when the nasal placodal edges proliferate?
They produce medial and lateral nasal prominences Leave the nasal placodes to lie in depressions known as nasal pits Pits will form the nostrils and nasal cavities Lateral nasal prominences form the alae (sides) of the nose
27
The maxillary prominences grow medially toward each other and the median nasal prominences which results in what?
Movement of the medial nasal prominences (MNP) toward the midline
28
What separates the lateral nasal prominence from the maxillary prominence?
A cleft known as the nasolacrimal groove By end of 6th week each MXP merges with the LNP at nasolacrimal groove Establishes continuity between the side of the nose (from LNP) and cheek region (MXP)
29
When do the medial nasal prominences merge with maxillary and lateral prominences?
Between weeks 7-10 | Results in continuity of the upper jaw and lip and separation of nasal pits from stomodeum
30
As the MNPs merge what forms?
The intermaxillary segment Permaxillary part of maxilla Primary palate Core of philtrum of upper lip while surface/skin of lip is from MXP
31
What does most of the upper lip, maxilla and secondary palate form from?
Maxillary prominences | Merge laterally with mandibular prominences
32
What does mesenchyme/mesoderm from PA2 form?
Facial muscles | Innervated by CN VII
33
What does mesenchyme/mesoderm in PA1 form?
Muscles of mastication | Innervated by CN V
34
Describe development of the nasal cavities
As the face develops surface depressions form on the FNP known as nasal placodes Will deepen due to proliferation of facial mesenchyme Placodes -> nasal pits -> primordial nasal sacs Sacs grow dorsally and ventrally to the developing forebrain
35
What separates the oral cavity from the nasal cavity?
The oronasal membrane which ruptures at the end of the 6th week connecting the cavities
36
What is palatogenesis?
Development of the palate from the primary and secondary palates in two stages Begins during the 6th week and completed by 12th week
37
When is the critical period for development of the palate?
End of 6th week to the beginning of the 9th week
38
Describe the role merging of the MNP has during palatogenesis
Merging of MNP forms the median palatine process (primary palate) Wedge shaped mass of mesenchyme Between the maxillary prominences Forms premaxillary part of the maxilla
39
When does formation of the secondary palate occur?
Early in 6th week from lateral palatine processes | Arise from mesenchyme of MxP
40
Describe formation of the secondary palate
Palatine processes extend inferiorly on each side of the tongue Mandible elongates -> pulls tongue forward and down in the mouth Palatine processes flip horizontally above the tongue (7-8th weeks)
41
Describe formation of the final palate
Bone gradually develops in the primary palate forming the premaxillary part of the maxilla which houses the incisors Bone extends from maxillae and palatine bones into lateral palatine processes to form the hard palate Posterior portions do not ossify -> extend posteriorly and fuse -> form soft palate (and uvula) Palatine raphe indicates the line of fusion
42
The nasopalatine canal persists in the median plane and is represented in the adult hard palate as what?
The incisive fossa
43
What is cleft lip?
Cleft extends through the upper lip Often clefting of the nose and/or maxilla Lack of fusion between maxillary prominences and median nasal prominences
44
What is cleft palate?
Clefts of secondary palate to incisive fossa May involve uvula and/or hard and soft palates Lack of fusion between lateral palatine processes with nasal septum or lateral palatine processes with median palatine process
45
Describe 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)
46
What is the medial lingual swelling (median tongue bud)?
Appears at the end of 4th week 1st indication of tongue development Triangular elevation in floor of primordial pharynx
47
What are the two lateral lingual swellings (distal tongue buds)?
Develop on each side of the median lingual swelling | Rapidly proliferate, merge and overgrow medial lingual swellings
48
All tongue buds result from what?
Proliferation of mesenchyme in ventromedial parts of PA1
49
Merged lateral lingual swellings form what?
The oral part of the tongue (anterior 2/3 of tongue)
50
Describe formation of the pharyngeal part of the tongue
Ventromedial parts of PA2 fuse forming the copula Ventromedial parts of PA3 and 4 develop the hypopharyngeal eminence Hypopharyngeal eminence overgrows the copula forming the posterior 1/3 of the tongue
51
Tongue musculature is derived from what?
Myoblasts of the occipital myotomes | Accompanied by CN XII to innervate the tongue
52
What is the terminal sulcus?
Line of fusion of anterior and posterior parts of the tongue
53
What are examples of tongue abnormalities?
Glossoschissis, ankyloglossia, macroglossia, and microglossia
54
What is glossooschissis?
Incomplete fusion of the lateral lingual swellings resulting in a bifid tongue
55
What is ankyloglossia?
Frenulum is short and extends to the tip of the tongue
56
What is macroglossia?
Excessively large tongue caused by generalized hypertrophy | Often seen in infants with Down syndrome
57
What is microglossia?
Abnormally small tongue (rare) and usually associated with micrognathia

NE Exam 1 (20 decks)

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