Embro: Face, Skull, Palate

Question 1

what gives rise to the skull?

Answer 1

neural crest cells form anterior portion (frontal, sq. temporal, sphenoid)
paraxial mesoderm forms posterior portion (parietal, occipital, pet. temporal)

Question 2

fontanelles

Answer 2

“soft spots” allow for growth of skull postnatally

• allow the calvaria to undergo changes in shape and molding during birthing
• anterior (largest, preda)
• Posterior (future site of lambda)
• posterolateral and anterolateral
• the flat bones grow together postnatally, but the cranial sutures will remain flexible thoughout childhood. the posterior/lateral close at 6 months. anterior fontanelle persists to 18 mos. of age

Question 3

craniosynostosis

Answer 3

“abnormal fibrous suture”
Cause: premature fusion of flat bones of skull
- doesn’t allow for brain and face to grow. in some cases it can imipede a vaginal delivery

Type 1:
Scaph

Question 4

scaphocephaly

Answer 4

• most common type of caniosyntosis
• where early fusion of coronal suture
• skull is long (A-P) and narrow (transversely)

Question 5

Brachycephaly

Answer 5

• coronal suture fuses

- skull is short (A-P) and wide laterally

Question 6

when does face form by?

Answer 6

week 8, face formation takes place in week 4-8. forms in a short period of time. this is the sensitive period in development where mother may not even know that she is pregnant. face is sensitive to teratogens –> craniofacial defects, clefts, infectious agents.

Question 7

How does face form?

Answer 7

1st pharyngeal arch - trigeminal n. : splits into three divisions

1. frontonasal prominence: forehead, bridge of nose and nasal septum, medial nasal prominences and lateral nasal prominences
2. maxillary prominences: upper cheek, lateral portions of upper lip
3. mandibular prominences: chin, lower cheek region, lower lip, part of external ear

• this is how we form our dermatomes

Question 8

How does nose form?

Answer 8

• nasal placodes (thickening of surface ectoderm) forms on frontonasal prominence and invaginate to form nasal pits
• mesenchyme surrounding the margins of the nasal pits proliferates to form the medial and lateral nasal prominences.
• medial nasal prominences are pushed forwards midline and will fuse to form intermaxillary segment
• the lateral nasal prominence stays open
• nose forms from medial and lateral nasal structures
• thus fusion occurs from frontonasal prominence, lateral nasal prominence and medial nasal prominence.

Question 9

how does upper lips form?

Answer 9

fusion from medial nasal prominences and maxillary prominences

Question 10

midline cleft of lip?

Answer 10

if two medial nasal promiences do not fuse

Question 11

anterior cleft?

Answer 11

• slightly off midline, occurs when maxillary prominence doesn’t fuse to medial nasal prominence or intermaxillary segment

Question 12

lower lips formation?

Answer 12

forms from two mandibular prominences. clefts here do not often occur

Question 13

how does nasolacrimal duct develop?

Answer 13

• the maxillary prominence fuses with the lateral nasal prominence along the nasolacrimal groove
• nasolacrimal duct forms from the ectoderm of nasolacrimal groove

Question 14

oblique facial cleft

Answer 14

if maxillary prominence doesn’t fuse to lateral nasal prominence
- runs from mouth towrads eye, it is a very large and severe cleft

Question 15

how does nasal cavity form?

Answer 15

nasal pits deepen to form nasal cavity. as nasal pit erodes mesochyme it gets close to neural tube. neural tube sends signals to upper mesoderm and triggers olfactory epithelium and CN I development from nasal sac ectoderm

Question 16

how does CN I develop?

Answer 16

from nasal sac ectoderm

Question 17

muscles of face?

Answer 17

muscles of mastication from first pharyngeal arch - CN V

muscles of facial expression from 2nd pharyngeal arch - CN VII

Question 18

primary palate formation

Answer 18

• formed from intermaxillary segment

- fuses with nasal septum above and lateral palatine shelves posteriorly

Question 19

secondary palate formation

Answer 19

• lateral palatine shelves form from maxillary prominences - these 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

Question 20

where is incisive foramen?

Answer 20

landmark between primary and secondary palates

Question 21

cleft of palate?

Answer 21

if two clefts don’t fuse midline

Question 22

anterior vs. posterior

Answer 22

anterior clefts are anterior to incisive foramen

posterior clefts are posterior to posterior foramen

Question 23

posterior cleft

Answer 23

posterior to incisive foramen
- lack of fusion of lateral palatine plates
“cleft palate”

Question 24

skull defects

Answer 24

due to neural crest defects

causes craniofacial defects - can be caused by “fetal alcohol syndrome”