Week 3: Skull embryology

Question 1

How many bones make up the neurocranium? How many bones make up the viscerocranium?

Answer 1

neurocranium = 8 bones viscerocranium = 14 bones

Question 2

What’re the bones of the neurocranium?

Answer 2

1. frontal 2. occipital 3. parietal (x2) 4. temporal (x2, including petromastoid bit) 5. sphenoid 6. ethmoid total = 8 bones of neurocranium

Question 3

What’re the bones of the viscerocranium?

Answer 3

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).

Question 4

What is the general function of the neurocranium?

Answer 4

To encase the brain and supporting structures for eyes/ ears

Question 5

The neurocranium is formed by 2 methods - what are they?

Answer 5

1. Endochondral ossification (chondrocranium) 2. Intramembranous ossification (calvaria)

Question 6

What is the ‘chondrocranium’?

Answer 6

the primary skull of vertebrates; composed of cartilage and replaced by bone (through process of endochondral ossification).

Question 7

What is the ‘calvaria’?

Answer 7

the top of the skull.

Question 8

What is the ‘basicranium’?

Answer 8

The cranial base or floor of the skull; underlies the brain.

Question 9

By what method is the basicranium formed?

Answer 9

via endochondral ossification

Question 10

By what method is the calvaria formed?

Answer 10

via intramembranous ossification

Question 11

The calvaria (top of the skull) is also known as what?

Answer 11

the membranous neurocranium (as it forms via intramembranous ossification)

Question 12

The formation of the neurocranium relies on signals coming from where?

Answer 12

The underlying developing neural tissue.

Question 13

What individual bones make up the basicranium (4)?

Answer 13

-ethmoid -sphenoid -petrous and mastoid parts of temporal bone -basiocciput of occipital bone

Question 14

The basicranial bones have cartilage models made of them. These are formed from what?

Answer 14

neural crest cells + mesoderm

Question 15

The basicranial bones develop from 3 pairs of midline cartilages - what are these called? List them from anterior to posterior.

Answer 15

1. prechordal (first midline pair) 2. hypophyseal (second midline pair) 3. parachordal (third midline pair)

Question 16

The basicranial bones form 3 lateral sensory capsules, what are these called?

Answer 16

1. olfactory sensory capsule 2. optic sensory capsule 3. otic sensory capsule

Question 17

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?

Answer 17

a.) prechordal b.) fuses with olfactory capsule c.) forms ethmoid + internal nose structures

Question 18

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?

Answer 18

a.) hypophyseal b.) fuses with optic capsule c.) forms wings + body of sphenoid (encases eye)

Question 19

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?

Answer 19

a.) parachordal b.) fuses with otic capsule c.) forms basiocciput and petrous + mastoid parts of temporal bone (around inner ear)

Question 20

What bones make up the calvaria?

Answer 20

-frontal -parietal -squamous part of occipital

Question 21

What is the calvaria formed from?

Answer 21

the calvaria is formed directly from neural crest cells.

Question 22

What forms between the bones of the calvaria during development?

Answer 22

Large, fibrous soft tissue sutures called fontanelles

Question 23

Intramembranous ossification of the neurocranium means making bone from what?

Answer 23

making bone directly from mesenchymal stem cells (neural crest cells).

Question 24

Endochondral ossification of the neurocranium means making bone from what?

Answer 24

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).

Question 25

The otic capsule is for developing the ability to do what?

Answer 25

hear sound

Question 26

The bones of the viscerocranium form within what?

Answer 26

Pharyngeal arches.

Question 27

How many pharyngeal arches are there?

Answer 27

5 total, 1-4 + 6 (as 5 is transitory; disappears)

Question 28

What do pharyngeal arches 1+2 form? (general answer)

Answer 28

structures of the face

Question 29

What does pharyngeal arch 3 form? (general answer)

Answer 29

face/ neck

Question 30

What do pharyngeal arch 4 and 6 form? (general answer)

Answer 30

neck structures

Question 31

Neural crest cells form all the cartilage and bone within which arches?

Answer 31

1-3

Question 32

By which ossification method does the viscerocranium develop?

Answer 32

BOTH endochondral and intramembranous ossification.

Question 33

What bones of the viscerocranium develop by endochondral ossification?

Answer 33

-small important bones -malleous, incus and stapes (from cartilage of arches 1+2) -styloid process of temporal bone (from cartilage in arch 1)

Question 34

What bones of the viscerocranium develop by intramembranous ossification?

Answer 34

-all viscerocranial bones except ossicles and styloid process of temporal bone -all formed from arch 1 neural crest cells

Question 35

What bones make up the ossicles?

Answer 35

malleous, incus and stapes

Question 36

The styloid process of temporal bone is part of (neuro/ viscerocranium).

Answer 36

viscerocranium

Question 37

The squamous part of temporal bone is part of (neuro/ viscerocranium).

Answer 37

viscerocranium

Question 38

The petrous + mastoid part of temporal bone is part of (neuro/ viscerocranium).

Answer 38

neurocranium

Question 39

The mandible develops (caudal/ rostral) to the neural tube. What does caudal mean in this context?

Answer 39

caudal to the tube. caudal means lower then.

Question 40

The first pharyngeal arch of the viscerocranium develops 2 prominences - what are these? What do they become?

Answer 40

1. mandibular prominence - lower jaw (mandible) 2. maxillary prominence (more rostral) - upper jaw (maxilla), nasal, zygomatic, palatine, squamous part of temporal bone

Question 41

Explain the meaning of the following term(s): a.) Dorsal b.) Ventral c.) Caudal d.) Rostral

Answer 41

a.) Dorsal - toward the back b.) Ventral - toward the belly c.) Caudal - toward the tail d.) Rostral - toward the nose

Question 42

The formation of the mouth and nose begins in which week of development?

Answer 42

4

Question 43

Explain the meaning of the following term(s): a.) Stomodeum b.) Primordia

Answer 43

a.) Stomodeum - primitive mouth b.) Primordia - structures that are newly developed and not fully formed

Question 44

How many facial primordia form around the stomodeum? What are these prominence's?

Answer 44

5. 2x maxillary prominences 2x mandibular prominences 1x frontonasal prominence

Question 45

Which facial primordia (prominence) is known to expand?

Answer 45

frononasal prominence

Question 46

The frontonasal prominence expands, developing what?

Answer 46

-nasal placodes (bilaterally) -lens placodes (laterally)

Question 47

The nasal placodes develop from the expanding frontonasal prominence. These nasal placodes develop ____ and _____ prominences.

Answer 47

medial and lateral prominences.

Question 48

The cleft between the first and second pharyngeal arch forms what?

Answer 48

the external ear.

Question 49

The medial nasal prominences fuse medially to form what?

Answer 49

intermaxillary segment (IMS)

Question 50

The intermaxillary segment (IMS) grows down and laterally, fusing with which prominence? When does this occur?

Answer 50

The IMS fuses with the maxillary prominence, in week 6-10.

Question 51

The IMS and maxillary prominence fuse to form what 2 structures?

Answer 51

1. dorsum of nose 2. philtrum

Question 52

Explain the meaning of the following term(s): Philtrum.

Answer 52

Rectangular area from under the nose to the midline of the upper lip.

Question 53

Congenital defects of the face are the result of what developmental failure?

Answer 53

failure of face prominences to correctly fuse with eachother.

Question 54

What does the primary palate form from?

Answer 54

the IMS.

Question 55

What does the secondary palate form from? Describe how this secondary palate forms.

Answer 55

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.

Question 56

Explain the meaning of the following term(s): Cleft palate.

Answer 56

-when palatine shelves fail to fuse -ie. primary palate unilateral or bilateral failure to fuse -ie. secondary palate fails to fuse in midline

Question 57

At birth, the skull comprises of how many seperate bones?

Answer 57

44.

Question 58

Fontanelle closure begins within how long since birth?

Answer 58

3 months

Question 59

Within what time frame does the anterior fontanelle close within?

Answer 59

Within the first 2 years of life.

Question 60

Why is it that neurocranial and viscerocranial bones grow at different rates?

Answer 60

cranial growth closely follows brain growth, whereas facial growth follows general body growth (takes longer, brain grows in size quicker)

Question 61

Where does bone growth (of skull) occur? (hint: this is a general question)

Answer 61

at sutures!

Question 62

Explain the meaning of the following term(s): Cranial vault.

Answer 62

The superior, lateral, and posterior walls of skull.

Question 63

The cranial vault achieves most of its growth within the early years of life. What percentage growth is complete by 5, and 15 years?

Answer 63

90% by 5 years 98% by 15 years

Question 64

How does maxillary and mandibular growth compare to growth of the cranial vault?

Answer 64

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.

Question 65

How do bones of the skull change as an individual grows older?

Answer 65

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.

Question 66

What occurs to the following bones/ bony features as an individual grows older... a.) Maxillae and mandible b.) Alveolar processes c.) Sutures

Answer 66

a.) Maxillae and mandible - become smaller, loss of teeth. b.) Alveolar processes - become absorbed. c.) Sutures - usually obliterated.

Question 67

Name the midline cartilage in red

Answer 67

Prechordal midline cartilage

Question 68

Name the midline cartilage in purple

Answer 68

Hypophyseal midline cartilage

Question 69

Name the midline cartilage in blue

Answer 69

Parachordal midline cartilage

Question 70

1

Answer 70

Prechordal Cartilage

Question 71

2

Answer 71

Hypophyseal cartilage

Question 72

3

Answer 72

Parachordal cartilage

Question 73

4

Answer 73

Olfactory capsule

Question 74

5

Answer 74

Olfactory epithelium

Question 75

6

Answer 75

Optic capsule

Question 76

7

Answer 76

Lense

Question 77

8

Answer 77

Optic cup

Question 78

9

Answer 78

Otic Vessicle

Question 79

10

Answer 79

Otic Capsule

Question 80

11

Answer 80

Notochord

Question 81

The red is signifying early stages of the ______ bone forming from neural crest cells

Answer 81

Frontal

Question 82

The Green is signifying early stages of the ______ bone forming from neural crest cells

Answer 82

Parietal

Question 83

The Blue is signifying early stages of the ______ bone forming from neural crest cells

Answer 83

The squamous of occipital

Question 84

1

Answer 84

Anterior Fontanelle

Question 85

2

Answer 85

Posterior Fontanelle

Question 86

3

Answer 86

Posterolateral Fontanelle

Question 87

4

Answer 87

Anterolateral Fontanelle

Question 88

What are the red and blue highlighted parts of the 1st pharyngeal arch?

Answer 88

Red: Maxillary prominences Blue: Mandibular prominences

Question 89

1, 2 and 3? what do they develop around? what are they collectively known as?

Answer 89

1. Frontonasal Prominence 2. Maxillary prominences (x2) 3. Mandibular prominences (x2) They develop around the stomodeum collectively known as the 5 face primordia

Question 90

4

Answer 90

Nasal placode

Question 91

5 and 6

Answer 91

5. Medial Nasal Prominence 6. Lateral Nasal Prominence

Question 92

7

Answer 92

Lens Placode

Question 93

Explain what is happening in this image in relation to the parts highlighted purple

Answer 93

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.

Question 94

Explain what is happening in this image in relation to the parts highlighted in red and blue.

Answer 94

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.

Question 95

Describe the pathology of these two images? Explain briefly what has happened in each.

Answer 95

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.