Skull, Face, Palate embryology Flashcards
Embryo of skull
Anterior portion of skull forms from neural crest; posterior portion from paraxial mesoderm.
Fontanelles
“Soft spots”; allow for growth of skull postnatally. 2. Allow the calvaria to undergo changes in shape (molding) during birthing. 3. Anterior; posterior; posterolateral; anterolateral 4. The flat bones grow together postnatally, but the cranial sutures remain flexible throughout childhood.
Craniosynostosis
Results from premature fusion of cranial sutures.
b. Scaphocephaly
- -1. Early fusion of sagittal suture.
- -2. Skull is long (A-P) and narrow (transverse)
c. Brachycephaly
- -1. Early fusion of coronal suture
- -2. Skull is short (A-P) and wide (transverse)
Embryology of the face
Three, paired facial prominences (from 1st arch) form most of the features of face:
- Frontonasal prominence
- Maxillary prominences
- Mandibular prominences
Frontonasal prominence becomes…
a. Forehead
b. Bridge of nose and nasal septum
c. Medial nasal prominences – apex of nose, philtrum of upper lip
d. Lateral nasal prominences – ala of nose 2
Maxillary prominences become…
upper cheek
lateral portions of upper lip
Mandibular prominences become:
chin, lower cheek region
lower lip
part of external ear
Development of nose and lips
- Nasal placodes (thickening of surface ectoderm) form on frontonasal prominence and then invaginate to form nasal pits.
- Mesenchyme surrounding the margins of the nasal pits proliferates to form the medial and lateral nasal prominences.
a. Medial nasal prominences are pushed towards midline and will fuse with one another (forming the intermaxillary segment).
b. The intermaxillary segment will fuse with the adjacent maxillary prominence to form upper lip.
c. The intermaxillary segment will also give rise to the philtrum and primary palate. - Thus, nose develops from frontonasal prominence, lateral nasal prominence, and medial nasal prominence.
- Upper lip develops from medial nasal prominences and maxillary prominences 5. Lower lip develops from mandibular prominences
development of the nasolacrimal duct
- The maxillary prominence fuses with the lateral nasal prominence along the nasolacrimal groove.
- The nasolacrimal duct forms from the ectoderm of nasolacrimal groove.
development of nasal cavities and paranasal sinuses
- Nasal pits deepen and grow dorsally, produce nasal sacs.
- Nasal sacs are separated from oral cavity by oronasal membrane.
- Oronasal membrane ruptures by 6th week; replaced by palate.
- Olfactory epithelium and CN I develop from nasal sac ectoderm.
- Paranasal sinuses develop slowly through puberty.
Face muscles development
Muscles of mastication from first pharyngeal arch (trigeminal n).
- Muscles of facial expression from 2nd pharyngeal arch (facial n)
Development of the primary palate
- During the 6th week the primary palate forms from the intermaxillary segment
- Fuses with nasal septum above and lateral palatine shelves posteriorly.
development of the secondary palate
Lateral palatine shelves form from maxillary prominences.
- Initially, the palatine shelves project inferomedially on each side of the tongue.
- During weeks 7-8, the palatine shelves migrate superiorly and fuse with one another, the primary palate, and in the midline with the nasal septum.
- Ossification occurs in anterior 2/3rds of palate to form hard palate.
- The incisive foramen is the landmark between primary and secondary palates.
Clefts of the lip and palate
are the most common craniofacial anomalies
Anterior cleft of lip/ palate
anterior to incisive foramen
A complete anterior cleft extends through the lip, alveolar part of maxilla to incisive fossa, separating primary from secondary palate. Caused by failure of maxillary prominence to fuse with medial nasal prominence (intermaxillary segment). b. Median cleft of lip: failure of medial nasal prominences to merge (rare)
