Embryology: Derivatives of Orofacial Structures Flashcards
1
Q
What does the cranium develop from?
A
Develops from mesenchyme around the developing brain
2
Q
Neurocranium
A
Bony case that encloses the brain; develops from mesenchyme
3
Q
Viscerocranium
A
Bones comprising the facial skeleton; develops from mesenchyme
4
Q
Intramembranous Ossification
A
Mesenchyme produces osseous tissue without cartilage formation
5
Q
Endochondral Ossification
A
Bone formation occurs using a cartilaginous intermediate
6
Q
Cartilaginous Neurocranium
A
- Several cartilages fuse, forming base of cranium (endochondral ossification)
7
Q
Cartilaginous Neurocranium: Order of Bone Formation
A
(1) Occipital Bone (base)
(2) Body of Sphenoid
(3) Ethmoid Bone
(4) Petrous and Mastoid parts of Temporal Bone
8
Q
Membranous Neurocranium
A
- Head mesenchyme at the sides and top of the brain
- Will form Calvaria (frontal & parietal bones) via intramembranous ossification
- Interconnected via sutures
9
Q
What does the Viscerocranium form?
A
Facial Skeleton
10
Q
Cartilaginous Viscerocranium
A
- PA1: malleus, incus
- PA2: stapes, styloid process of temporal bone, lesser horns of the hyoid
- PA3: greater horns of the hyoid
- PA4: cartilages fuse to form laryngeal cartilages (thyroid and epiglottal cartilages)
11
Q
___ form bones and connective tissue of craniofacial structures
A
NCCs
12
Q
Membranous Viscerocranium
A
- Intramembranous ossification within Maxillary prominence forms: Squamous Temporal, Maxillary, and Zygomatic bones
- Cells of mandibular prominence form the mandible
13
Q
Cartilaginous means the structures formed via ___ Ossification
A
Endochondral
14
Q
Membranous means the structures formed via ___ Ossification
A
Intramembranous
15
Q
___ ___ Bones become part of the Neurocranium (initially form as part of Viscerocranium)
A
Squamous Temporal
16
Q
Trigonocephaly
A
- Premature closure of the frontal (metopic) suture
- Results in malformation of anteriormost portion of Frontal and Orbital bones (gives frontal bone a triangular shaped appearance)
17
Q
Scaphocephaly
A
- Premature closure of Sagittal suture; only allows anterior and posterior growth, can’t expand along the midline/sagittal suture
- Results in long, narrow and wedge-shaped cranium
- Occurs in 50% of Craniosynostosis cases
18
Q
Brachycephaly
A
- Premature closure of the Coronal Suture
- Results in a high, tower-like cranium
- Second most common form of Craniosynostosis
19
Q
Plagiocephaly
A
- Premature closure of the right or left coronal or lambdoid suture (UNILATERAL)
- Results in cranium that is twisted and asymmetric in appearance; slanting of head when looking from superior view
20
Q
When do facial primordia appear?
A
Early in the 4th week
21
Q
What triggers the formation/development of Facial Primordia? When does this occur?
A
- Disintegration/rupturing of Oropharyngeal Membrane (membrane that initially covered the stomodeum, separating the primordial pharynx from the facial primordia)
- Ruptures at 26 days
22
Q
What are the 5 Facial Primordia that appear early in the 4th week as prominences around the Stomodeum (primitive mouth)?
A
- Maxillary Prominences (x2)
- Mandibular Prominences (x2)
- Frontonasal Prominence (x1)
23
Q
What weeks does facial development typically occur?
A
During 4th-8th weeks
24
Q
When is palate formation complete?
A
Week 12
25
Facial Primordia: Frontonasal Prominence (FNP)
- Receives contributions from/populated by forebrain and midbrain NCCs
- Surrounds ventrolateral part of the forebrain
- Frontal portion will form the forehead
- Nasal portion forms rostral boundary of stomodeum and nose
26
What PA do the Maxillary and Mandibular Prominences arise from?
PA1 splits to form these two prominences
27
Facial Primordia: Maxillary Prominences (MXP)
- Arises from PA1
- Forms lateral boundaries of stomodeum
- Populated by NCCs from midbrain and hindbrain
28
Facial Primordia: Mandibular Prominences (MDP)
- Arises from PA1
- Forms caudal boundary of stomodeum
- Populated by NCCs from midbrain and hindbrain
29
What are the first parts of the face to form?
Lower Jaw and Lower Lip
30
What occurs in order for the lower jaw and lower lip to form?
(1) Oropharyngeal membrane disintegrates
(2) Extension and fusion of the two mandibular prominences toward/at the midline -- sometimes can leave dimple in middle of chin (if this doesn't happen then would have cleft in face)
31
By the end of the 4th week, ___ ___ form on inferolateral parts of the FNP
Nasal Placodes (NP)
32
Nasal Placodes
Bilateral oval thickenings of the surface ectoderm that are primordia of the nasal epithelium; distinctly geared towards sensation; arise from FNP
33
Sensory structures (nose, eyes, ears) arise from ___
Placodes
(specialized areas of surface ectoderm)
34
Formation of Nasal Pit from Nasal Placodes
(1) Placodal edges proliferate
(2) Produce MNP and LMP
(3) Nasal placodes now lie deep in depressions and are called Nasal Pits
------------------
(1) NPs "dig themselves" deeper, dorsally, into the underlying mesenchyme
(2) The "digging" forms ridges/prominences on each side (medial and lateral side) of the placodes
(3) Divison of FNP into the Medial Nasal Prominence (MNP) and the Lateral Nasal Prominence (LNP)
(4) Space/indention between the Medial and Lateral Nasal Prominences continues to grow deeper and forms the Nasal Pits
35
What do the Nasal Pits give rise to?
- Nostrils
- Nasal Cavities
36
What does the Lateral Nasal Prominence eventually give rise to?
Tissue comprising the sides of the nose -- Ala of the nose
37
What happens if a Lateral and/or Medial Nasal Prominence is truncated/reduced in size?
Results in a nasal malformation
38
What causes movement of the MNPs toward the midline?
Maxillary Prominences growing medially towards each other and the Medial Nasal Prominences
39
Lateral Nasal Prominence is separated from the Maxillary Prominence by a cleft, the ___ ___
Nasolacrimal Groove
40
By the end of the ___ week, each MXP merges with the LNP at the nasolacrimal groove
6th
41
What does the merging of the MXP and LNP at the nasolacrimal groove establish?
Continuity between the side of the nose and cheek region
42
What happens between weeks 7-10 in regards to the MNP and the Maxillary + LNPs?
MNP merges/fuses with its correlating Maxillary + LNP
43
What does the Maxillary Prominence give rise to?
- Most of the upper lip
- Maxilla
- Secondary Palate
44
MXP merging with MNP results in:
Continuity of the upper jaw and lip, and separation of nasal pits from stomodeum
45
As MNPs merge with the MXP + LNPS, the ___ ___ forms
Intermaxillary Segment
46
Intermaxillary Segment
- Premaxillary part of maxilla
- Primary plate
- "Core" of philtrum of upper lip, while surface of lip is from MXP
47
Nasal Placodes deepen into Nasal Pits due to the proliferation of facial ___
Mesenchyme
48
Nasal Placodes -> Nasal Pits -> ___ ___ ___
Primordial Nasal Sacs
49
Primordial Nasal Sacs
- Sacs that grow dorsally and ventral to the developing forebrain
- Separated from the oral cavity by the Oronasal Membrane
50
When does the Oronasal Membrane rupture? What does this result in?
- End of 6th week
- Connecting of the nasal cavity to the oral cavity
51
When does Palatogenesis (formation of palate) begin? When does it end? When is the critical period?
- Begins 6th week, completed by 12th week
- Critical period from end of 6th week to beginning of 9th week
52
Merging of the MNP forms the:
Median Palatine Process (Primary Plate)
53
Median Palatine Process (Primary Plate)
- Wedge-shaped mass of mesenchyme
- Located between the maxillary prominences
- Forms the premaxillary part of the maxilla
54
When does Secondary Palate formation begin?
Early in the 6th week
55
What does the Secondary Palate develop from?
Lateral Palatine Processes (arise from mesenchyme of MXP)
56
Formation of Secondary Palate
(1) Palatine processes extend inferiorly on each side of the tongue
(2) Mandible elongates which pulls the tongue forward and down in the mouth
(3) Palatine processes "flip" horizontally above the tongue (occurs around 7-8wks); this allows the palate to grow towards midline and fuse (Palatal shelf fuses in Anterior to Posterior direction)
57
Formation of the Final Palate
- Completion of the fusion of the primary and secondary palates
- Bone gradually develops in the primary palate, forming the premaxillary part of the maxilla which houses the incisors
- Formation of hard and soft palate
- Nasopalatine canal persists in medial plane
58
How is the hard plate formed?
Bone extends from maxillae and palatine bones into lateral palatine processes to form the hard palate
59
How is the soft palate formed?
Posterior portions of the Lateral Palatine Processes do not ossify, but instead continue to extend posteriorly and fuse, thus forming the soft palate and uvula
60
Nasopalatine persists in the medial plane and is represented in the adult hard palate by the:
Incisive Fossa
61
Cleft Lip
- Cleft extends through upper lip
- Often clefting of the nose and/or maxilla
- Lack of fusion between maxillary prominences and medial nasal prominences
62
Cleft Palate
- Clefts of secondary palate to incisive fossa
- May involve uvula and/or hard and soft palates
63
Cleft Palate forms due to lack of fusion between:
(1)
(2)
(1) Lateral Palatine Processes with nasal spetum
(2) Lateral Palatine Processes with Median Palatine Process
64
Nasal Septum
Down growth from internal parts of merged medial nasal prominences
65
When does fusion of the nasal septum and palatine process begin anteriorly? When is it completed posteriorly?
- 9th week
- 12th week
66
When does the Median Tongue Bud appear?
End of 4th week
67
Median Tongue Bud
- Triangular mesenchymal swelling in floor of primordial pharynx
- 1st indication of tongue development
68
What happens after the Medial Tongue Bud appears?
Two distal tongue buds (lateral lingual swellings) develop on each side of the median tongue bud -- mesenchymal swelling that eventually overgrows median tongue bud
69
Merged distal tongue buds form the:
Oral Part, anterior 2/3 of the tongue (line down the middle of the tongue, medial sulcus, marks the fusion point)
70
Formation of the Pharyngeal Part (Posterior 1/3) of the Tongue:
- PA2 develops a midline swelling, the Copula
- Copula is overgrown by the Hypopharyngeal Eminence, swelling of PA3 (major) and PA4 (minor)
71
Terminal Sulcus
Line of fusion of the anterior and posterior parts of the tongue
72
Tongue musculature is derived from myoblasts of the ____ myotomes
Occipital (CN XII motor innervation)
73
Glossoschissis
- Incomplete fusion of the lateral lingual swellings
- Results in a bifid tongue
74
Ankyloglossia
- Frenulum is short and extends to the tip of the tongue
- "Tongue tied"
75
Macroglossia
- Excessively large tongue caused by generalized hypertrophy
- Often seen in infants with down syndrome
76
Microglossia
- Abnormally small tongue (rare)
- Usually associated with Micrognathia
77
Intermediate Structure: Median Tongue Bud
(1) Embryonic Precursor:
(2) Adult Structure:
(3) Innervation:
(1) Embryonic Precursor: PA1
(2) Adult Structure: Overgrown by lateral lingual swellings
(3) Innervation: Lingual branch (sensory) of mandibular division of Trigeminal N (CN V)
78
Intermediate Structure: Lateral Lingual Swellings
(1) Embryonic Precursor:
(2) Adult Structure:
(3) Innervation:
(1) Embryonic Precursor: PA1
(2) Adult Structure: Muscosa of anterior 2/3 of tongue
(3) Innervation: Chord Tympani from Facial N (CN VII; innervates all taste buds EXCEPT Vallate Papillae)
79
Intermediate Structure: Copula
(1) Embryonic Precursor:
(2) Adult Structure:
(3) Innervation:
(1) Embryonic Precursor: PA2
(2) Adult Structure: Overgrown by other strucutres
(3) Innervation: ----
80
Intermediate Structure: Large, Ventral Part of Hypopharyngeal Eminence
(1) Embryonic Precursor:
(2) Adult Structure:
(3) Innervation:
(1) Embryonic Precursor: PA3
(2) Adult Structure: Posterior 1/3 of tongue
(3) Innervation: Sensory branch of Glossopharyngeal N (CN IX; also supplies vallate papillae)
81
Intermediate Structure: Small, Dorsal Part of Hypopharyngeal Eminence
(1) Embryonic Precursor:
(2) Adult Structure:
(3) Innervation:
(1) Embryonic Precursor: PA4
(2) Adult Structure: Small region on dorsal side of posterior 1/3 of tongue
(3) Innervation: Sensory fibers of Superior Laryngeal branch of Vagus N (CN X)
82
Embryonic Precursor: Occipital Somites
(1) Intermediate Structure:
(2) Adult Structure:
(3) Innervation:
(1) Intermediate Structure: Myoblasts
(2) Adult Structure: Intrinsic and most extrinsic muscles of tongue
(3) Innervation: Hypoglossal N (CN XII)
83
Embryonic Precursor: Head Mesoderm
(1) Intermediate Structure:
(2) Adult Structure:
(3) Innervation:
(1) Intermediate Structure: Myoblasts
(2) Adult Structure: Palatoglossus muscle
(3) Innervation: Pharyngeal Plexus of Vagus N (CN X)
