Week 3: Skull embryology Flashcards
How many bones make up the neurocranium? How many bones make up the viscerocranium?
neurocranium = 8 bones viscerocranium = 14 bones
What’re the bones of the neurocranium?
- frontal 2. occipital 3. parietal (x2) 4. temporal (x2, including petromastoid bit) 5. sphenoid 6. ethmoid total = 8 bones of neurocranium
What’re the bones of the viscerocranium?
2x nasal 2x lacrimal 2x inferior nasal concha 2x maxilla 2x zygomatic 2x palatine 1x vomer 1x mandible total = 14 bones of viscerocranium (note: squamous part of temporal bone is part of viscerocranium, but not one of the 14 as temporal bone is neurocranial).
What is the general function of the neurocranium?
To encase the brain and supporting structures for eyes/ ears
The neurocranium is formed by 2 methods - what are they?
- Endochondral ossification (chondrocranium) 2. Intramembranous ossification (calvaria)
What is the ‘chondrocranium’?
the primary skull of vertebrates; composed of cartilage and replaced by bone (through process of endochondral ossification).
What is the ‘calvaria’?
the top of the skull.
What is the ‘basicranium’?
The cranial base or floor of the skull; underlies the brain.
By what method is the basicranium formed?
via endochondral ossification
By what method is the calvaria formed?
via intramembranous ossification
The calvaria (top of the skull) is also known as what?
the membranous neurocranium (as it forms via intramembranous ossification)
The formation of the neurocranium relies on signals coming from where?
The underlying developing neural tissue.
What individual bones make up the basicranium (4)?
-ethmoid -sphenoid -petrous and mastoid parts of temporal bone -basiocciput of occipital bone
The basicranial bones have cartilage models made of them. These are formed from what?
neural crest cells + mesoderm
The basicranial bones develop from 3 pairs of midline cartilages - what are these called? List them from anterior to posterior.
- prechordal (first midline pair) 2. hypophyseal (second midline pair) 3. parachordal (third midline pair)
The basicranial bones form 3 lateral sensory capsules, what are these called?
- olfactory sensory capsule 2. optic sensory capsule 3. otic sensory capsule
Basicranial bones develop from 3 pairs of midline cartilages. Consider the first midline pair. What does/ is it… a.) AKA? b.) fuse with? c.) form?
a.) prechordal b.) fuses with olfactory capsule c.) forms ethmoid + internal nose structures
Basicranial bones develop from 3 pairs of midline cartilages. Consider the second midline pair. What does/ is it… a.) AKA? b.) fuse with? c.) form?
a.) hypophyseal b.) fuses with optic capsule c.) forms wings + body of sphenoid (encases eye)
Basicranial bones develop from 3 pairs of midline cartilages. Consider the third midline pair. What does/ is it… a.) AKA? b.) fuse with? c.) form?
a.) parachordal b.) fuses with otic capsule c.) forms basiocciput and petrous + mastoid parts of temporal bone (around inner ear)
What bones make up the calvaria?
-frontal -parietal -squamous part of occipital
What is the calvaria formed from?
the calvaria is formed directly from neural crest cells.
What forms between the bones of the calvaria during development?
Large, fibrous soft tissue sutures called fontanelles
Intramembranous ossification of the neurocranium means making bone from what?
making bone directly from mesenchymal stem cells (neural crest cells).
Endochondral ossification of the neurocranium means making bone from what?
A cartilage model which is replaced over time by bone. The cartilage model itself is made from neural crest cells + mesoderm. The emphasis with these questions is that for intramembranous ossification, bone is made directly from neural crest cells. Whereas with endochondral ossification, neural crest cells + mesodermal tissue must be used to first create a cartilage model (which will later be ossified).
The otic capsule is for developing the ability to do what?
hear sound
The bones of the viscerocranium form within what?
Pharyngeal arches.
How many pharyngeal arches are there?
5 total, 1-4 + 6 (as 5 is transitory; disappears)
What do pharyngeal arches 1+2 form? (general answer)
structures of the face
What does pharyngeal arch 3 form? (general answer)
face/ neck
What do pharyngeal arch 4 and 6 form? (general answer)
neck structures
Neural crest cells form all the cartilage and bone within which arches?
1-3
By which ossification method does the viscerocranium develop?
BOTH endochondral and intramembranous ossification.
What bones of the viscerocranium develop by endochondral ossification?
-small important bones -malleous, incus and stapes (from cartilage of arches 1+2) -styloid process of temporal bone (from cartilage in arch 1)
What bones of the viscerocranium develop by intramembranous ossification?
-all viscerocranial bones except ossicles and styloid process of temporal bone -all formed from arch 1 neural crest cells
What bones make up the ossicles?
malleous, incus and stapes
The styloid process of temporal bone is part of (neuro/ viscerocranium).
viscerocranium
The squamous part of temporal bone is part of (neuro/ viscerocranium).
viscerocranium
The petrous + mastoid part of temporal bone is part of (neuro/ viscerocranium).
neurocranium
The mandible develops (caudal/ rostral) to the neural tube. What does caudal mean in this context?
caudal to the tube. caudal means lower then.
The first pharyngeal arch of the viscerocranium develops 2 prominences - what are these? What do they become?
- mandibular prominence - lower jaw (mandible) 2. maxillary prominence (more rostral) - upper jaw (maxilla), nasal, zygomatic, palatine, squamous part of temporal bone
Explain the meaning of the following term(s): a.) Dorsal b.) Ventral c.) Caudal d.) Rostral
a.) Dorsal - toward the back b.) Ventral - toward the belly c.) Caudal - toward the tail d.) Rostral - toward the nose
The formation of the mouth and nose begins in which week of development?
4
Explain the meaning of the following term(s): a.) Stomodeum b.) Primordia
a.) Stomodeum - primitive mouth b.) Primordia - structures that are newly developed and not fully formed
How many facial primordia form around the stomodeum? What are these prominence’s?
- 2x maxillary prominences 2x mandibular prominences 1x frontonasal prominence
Which facial primordia (prominence) is known to expand?
frononasal prominence
The frontonasal prominence expands, developing what?
-nasal placodes (bilaterally) -lens placodes (laterally)
The nasal placodes develop from the expanding frontonasal prominence. These nasal placodes develop ____ and _____ prominences.
medial and lateral prominences.
The cleft between the first and second pharyngeal arch forms what?
the external ear.
The medial nasal prominences fuse medially to form what?
intermaxillary segment (IMS)
The intermaxillary segment (IMS) grows down and laterally, fusing with which prominence? When does this occur?
The IMS fuses with the maxillary prominence, in week 6-10.
The IMS and maxillary prominence fuse to form what 2 structures?
- dorsum of nose 2. philtrum
Explain the meaning of the following term(s): Philtrum.
Rectangular area from under the nose to the midline of the upper lip.
Congenital defects of the face are the result of what developmental failure?
failure of face prominences to correctly fuse with eachother.
What does the primary palate form from?
the IMS.
What does the secondary palate form from? Describe how this secondary palate forms.
The secondary palate forms from the maxillary prominence. The maxillary prominence forms two internal and lateral palatine shelves. These two shelves grow toward each other and fuse in the midline, forming the secondary palate.
Explain the meaning of the following term(s): Cleft palate.
-when palatine shelves fail to fuse -ie. primary palate unilateral or bilateral failure to fuse -ie. secondary palate fails to fuse in midline
At birth, the skull comprises of how many seperate bones?
44.
Fontanelle closure begins within how long since birth?
3 months
Within what time frame does the anterior fontanelle close within?
Within the first 2 years of life.
Why is it that neurocranial and viscerocranial bones grow at different rates?
cranial growth closely follows brain growth, whereas facial growth follows general body growth (takes longer, brain grows in size quicker)
Where does bone growth (of skull) occur? (hint: this is a general question)
at sutures!
Explain the meaning of the following term(s): Cranial vault.
The superior, lateral, and posterior walls of skull.
The cranial vault achieves most of its growth within the early years of life. What percentage growth is complete by 5, and 15 years?
90% by 5 years 98% by 15 years
How does maxillary and mandibular growth compare to growth of the cranial vault?
Maxillary and mandibular growth is roughly even throughout the first 20 years of life. This contrasts to that of the cranial vault, which completes most of its growth within the first 5 years of life.
How do bones of the skull change as an individual grows older?
Bones generally become thinner and lighter as an individual grows older. However - some parts do get thicker due to increased growth of the ‘inner table’ (endosteum) of bone.
What occurs to the following bones/ bony features as an individual grows older… a.) Maxillae and mandible b.) Alveolar processes c.) Sutures
a.) Maxillae and mandible - become smaller, loss of teeth. b.) Alveolar processes - become absorbed. c.) Sutures - usually obliterated.
Name the midline cartilage in red
Prechordal midline cartilage
Name the midline cartilage in purple
Hypophyseal midline cartilage
Name the midline cartilage in blue
Parachordal midline cartilage
1
Prechordal Cartilage
2
Hypophyseal cartilage
3
Parachordal cartilage
4
Olfactory capsule
5
Olfactory epithelium
6
Optic capsule
7
Lense
8
Optic cup
9
Otic Vessicle
10
Otic Capsule
11
Notochord
The red is signifying early stages of the ______ bone forming from neural crest cells
Frontal
The Green is signifying early stages of the ______ bone forming from neural crest cells
Parietal
The Blue is signifying early stages of the ______ bone forming from neural crest cells
The squamous of occipital
1
Anterior Fontanelle
2
Posterior Fontanelle
3
Posterolateral Fontanelle
4
Anterolateral Fontanelle
What are the red and blue highlighted parts of the 1st pharyngeal arch?
Red: Maxillary prominences
Blue: Mandibular prominences
1, 2 and 3? what do they develop around? what are they collectively known as?
- Frontonasal Prominence
- Maxillary prominences (x2)
- Mandibular prominences (x2)
They develop around the stomodeum
collectively known as the 5 face primordia
4
Nasal placode
5 and 6
- Medial Nasal Prominence
- Lateral Nasal Prominence
7
Lens Placode
Explain what is happening in this image in relation to the parts highlighted purple
Purple: Medial Nasal Prominences
In this image the medial nasal promiences are fusing medially to form the intermaxillary segement, this segment grows down and laterally and fuses with maxillary prominence to form the dorsum of the nose and the philtrum.
Explain what is happening in this image in relation to the parts highlighted in red and blue.
Red: Primary palate (from intermaxillary segment)
Blue: Secondary palate (from maxillary prominence)
The Secondary palate forms two internal, lateral palatine shelves that will grow towards each other and fuse in the midline with the primary palate.
Describe the pathology of these two images? Explain briefly what has happened in each.
In the top image: The primary and secondary palates have failed to fuse resulting in what is known as cleft lip.
In the bottom image: The palatine shelves have failed to fuse resulting in cleft palate.
