development of face and skull Flashcards
What can be seen by the end of the 5th week?
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
what is the stomodeum?
the forming and developing oral cavity
how is the frontal nasal process formed?
Formed by mesenchymal proliferation ventral to forebrain -
- initially the cranial boundary of stomodeum
how are nasal pits formed?
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
what occurs in weeks 6-7 of formation of the face?
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
what does the intermaxillary segment give rise to?
Philtrum on upper lip
Premaxilla (site of upper incisor development)
Primary palate
what is this?
intermaxillary segment
what does the frontonasal process form?
forehead, dorsum and apex of nose
what does the maxillary process form?
upper cheeks, most of maxilla, secondary/definite palate and upper lip
what does the mandibular process form?
lower cheeks, mandible and lower lip
what occurs during the initial formation of the nasal passages?
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
how is the nasal duct formed?
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
where neurocranium
where viscerocranium
Neurocranium
- Protective case for the brain
- Black and white
Viscerocranium
- Jaw skeleton
- Blue
what is chondrocranium?
what types?
Cartilagenous neurocranium
- Parachordal cartilage
- Hypophyseal cartilages
- Prechordal cartilages
how does the base of the skull form?
fusion of 3 cartilages
- Prechordal
- Hypophyseal
- Parachordal
what does parachordal cartilage do?
formation of skull base
Forms at cranial end of notochord
Forms boundaries of foramen magnum and base of occipital bone
what does hypohyseal cartilage do?
formation of base of skull
- 2 cartilages form around developing pituitary gland
- Fuse to form sella turcica and body of sphenoid bone
what do prechordal cartilages do?
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
where are sensory capsules derived from?
from paraxial mesoderm and neural crest
where does nasal capsule form
what does it form?
Develops around nasal sacs
Forms nostril cartilages, conchae and parts of ethmoid
where does otic capsules form?
what do they do
what do they form?
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
what is A
Fontanelle -
- areas where sutures are well separated
- unfused soft fibrous sutures
- separate bones of the skull cap
how is the mesnechymal layer (dermis) covering the brain mineralised?
They mineralise due to the formation of the bone spicules
