development of face and skull

Question 1

What can be seen by the end of the 5th week?

Answer 1

5 facial processes appear by the end of week 5 around stomodeum (B)

A = unpaired frontonasal process

C = 2 maxillary processes

D = 2 mandibular processes

Question 2

what is the stomodeum?

Answer 2

the forming and developing oral cavity

Question 3

how is the frontal nasal process formed?

Answer 3

Formed by mesenchymal proliferation ventral to forebrain -

• initially the cranial boundary of stomodeum

Question 4

how are nasal pits formed?

Answer 4

Ectoderm at centre of nasal placodes enlarge and

Invaginate/grow together to form nasal pits

Raised horseshoe rim of placodes divide into

• Lateral nasal process
• Medial nasal process

Question 5

what occurs in weeks 6-7 of formation of the face?

Answer 5

Medial nasal processes -red

• Migrate toward each other
• Fuse to form primordia of nasal bridge and septum

Maxillary processes merge with lateral nasal processes -yellow

• Sides of nose start to form
• Start to form around week 6 and 7

Inferior tips of medial nasal processes expand laterally and inferiorly, fusing to form intermaxillary segment

Tips of maxillary processes grow to meet intermaxillary segment and fuse together

Question 6

what does the intermaxillary segment give rise to?

Answer 6

Philtrum on upper lip

Premaxilla (site of upper incisor development)

Primary palate

Question 7

what is this?

Answer 7

intermaxillary segment

Question 8

what does the frontonasal process form?

Answer 8

forehead, dorsum and apex of nose

Question 9

what does the maxillary process form?

Answer 9

upper cheeks, most of maxilla, secondary/definite palate and upper lip

Question 10

what does the mandibular process form?

Answer 10

lower cheeks, mandible and lower lip

Question 11

what occurs during the initial formation of the nasal passages?

Answer 11

Nasal pits deepen due to growth of the facial processes

Behind openings, pits fuse to form single enlarged ‘sac’ posterior to intermaxillary process

Floor of nasal ‘sac’ proliferates to form thickened plate separating nasal ‘sac’ from oral cavity - nasal fin

Nasal fin thins during growth due to developing vacuoles forming oronasal (bucconasal) membrane

Question 12

how is the nasal duct formed?

Answer 12

ctoderm of floor of nasolacrimal groove thickens to form solid epithelial cord

• Nasolacrimal groove = Cleft between lateral nasal process and adjacent maxillary processes

Cord sinks into mesenchyme and canalises to form tube - nasolacrimal duct

Cranial end expands to form lacrimal sac

Duct drains into nasal cavity and invests with bone

Question 13

where neurocranium

where viscerocranium

Answer 13

Neurocranium

• Protective case for the brain
• Black and white

Viscerocranium

• Jaw skeleton
• Blue

Question 14

what is chondrocranium?

what types?

Answer 14

Cartilagenous neurocranium

• Parachordal cartilage
• Hypophyseal cartilages
• Prechordal cartilages

Question 15

how does the base of the skull form?

Answer 15

fusion of 3 cartilages

• Prechordal
• Hypophyseal
• Parachordal

Question 16

what does parachordal cartilage do?

Answer 16

formation of skull base

Forms at cranial end of notochord

Forms boundaries of foramen magnum and base of occipital bone

Question 17

what does hypohyseal cartilage do?

Answer 17

formation of base of skull

• 2 cartilages form around developing pituitary gland
• Fuse to form sella turcica and body of sphenoid bone

Question 18

what do prechordal cartilages do?

Answer 18

formation of the base of the skull

• 2 cartilages form at cranial end of brain base
• Fuse to form body of ethmoid bone and contributes to nasal septum

Question 19

where are sensory capsules derived from?

Answer 19

from paraxial mesoderm and neural crest

Question 20

where does nasal capsule form

what does it form?

Answer 20

Develops around nasal sacs

Forms nostril cartilages, conchae and parts of ethmoid

Question 21

where does otic capsules form?

what do they do

what do they form?

Answer 21

Form around developing otic vesicle

Fuse with parts of parachordal cartilages to form periotic capsules - later ossify as petrous and mastoid part of temporal bones

Question 22

what is A

Answer 22

Fontanelle -

• areas where sutures are well separated
• unfused soft fibrous sutures
  
  • separate bones of the skull cap

Question 23

how is the mesnechymal layer (dermis) covering the brain mineralised?

Answer 23

They mineralise due to the formation of the bone spicules