2 - Functional Anatomy of Cranial Sutures

Question 1

What type of joint is a cranial suture?

Answer 1

Fibrous synarthrotic joints

Question 2

The skull is formed from two types of bone - what are they both called?

Answer 2

1) Endochondral bones

2) Dermal bones

Question 3

How does endochrondral bone develop?

Answer 3

From cartilaginous precursors.

Question 4

How does dermal bone develop?

Answer 4

Ossifies directly from mesenchyme.

Question 5

What groups of bones form the dermal bone subset?

Answer 5

Bones of the face

Bones of the cranial vault

Question 6

What groups of bones form the endochondral group?

Answer 6

Higher laryngeal skeleton

Cranial base bones

Question 7

What two developmental tissue origins does the skull form bone from?

Answer 7

Neural crest tissue

Mesoderm

Question 8

What parts of the skull are derived from mesoderm?

Answer 8

Brain case

cranial vault + floor

Question 9

What parts of the skull are derived from neural crest tissue?

Answer 9

Facial skeleton

Upper laryngeal skeleton

Question 10

What are the 3 developmental parts of the skull?

Answer 10

1) Chondrocranium
2) Splanchnocranium
3) Dermatocranium

Question 11

The chondrocranium is involved in the development of bone associated with which skull feature?

Answer 11

Bones involved with special senses

Question 12

The dermatocranium is involved functionally with the development of which skull bones?

What is the function?

Answer 12

Cranial vault + facial skeleton

Mastication

Question 13

What are the 3 developmental contributions of the chondrocranium?

Answer 13

1) 3 pairs of cartilaginous precursors
2) Capsules for sensory organs
3) Occipital cartilages

Question 14

What are the 3 pairs of cartilaginous precursors?

Answer 14

1) Prechordal
2) Hypophyseal
3) Parachordal

Question 15

What structure is the splanchocranium associated with?

Answer 15

Pharyngeal arches

Question 16

How many pharyngeal arches did humans used to have?

How many do they now have?

Answer 16

6

Now have 5.

Question 17

What direction do the pharyngeal arches form?

Answer 17

Cranio-caudal succession.

Question 18

What pharyngeal arch is no longer present?

Answer 18

No. 5

Question 19

What are the 4 parts to each pharyngeal arch?

Answer 19

1) Ectoderm (outside)
2) Mesenchymal core
3) Endoderm (inside)
4) Cartilaginous skeletal element

Question 20

Where does the cartilaginous skeletal element form from?

Answer 20

Neural crest tissue

Question 21

What are the 3 possible fates of this skeletal element within the pharyngeal arches?

Answer 21

1) Ossify into bone
2) Stay as cartilage
3) Regress by parturition (act as a scaffold)

Question 22

What day does the first pharyngeal arch form?

Answer 22

Day 22

Question 23

The first pharyngeal arch gives rise to two prominences, what are they called?

Answer 23

Maxillary prominence (Palatopterygoquadrate)

Mandibular prominence (Meckel’s cartilage)

Question 24

What 2 bony structures does the maxillary prominence give rise to?

Answer 24

Maxilla

Palate

Question 25

What bone does the mandibular arch give rise to?

Answer 25

Mandible

Question 26

What muscles does the first pharyngeal arch also give rise to?

Answer 26

Muscles of mastication

Question 27

In the formation of the mandible, what cartilage is used as a template / scaffold but does NOT contribute directly to its formation?

Answer 27

Meckel's cartilage | in mandibular prominence

Question 28

What two bones does Meckel's cartilage give rise to? What two cartilages does Meckel's cartilage give rise to?

Answer 28

Incus Malleus Sphenomandibular ligament. Anterior ligament of malleus.

Question 29

What ossification process is used in the formation of the mandible?

Answer 29

Perichondral ossification (out-to-in)

Question 30

Give 3 examples of composite bones?

Answer 30

1) Sphenoid 2) Temporal 3) Occipital

Question 31

What bones make up the temporal bone?

Answer 31

(Dermatocranium) - Tympanic - Squamosal (Chondrocranium) - Petromastoid (Splanchnocranium) - Styloid

Question 32

What evolutionary features of the skull can be found before birth?

Answer 32

1) Orbits fully sized 2) Otic capsule fully developed 3) Negative allometry

Question 33

What changes occur to the skull following birth?

Answer 33

1) Braincase volume increases 2) Facial height increases 3) Positive allometry

Question 34

What are 2 functions of fontanelles?

Answer 34

1) Ease of parturition | 2) Permits brain growth

Question 35

What type of joints are fontanelles?

Answer 35

Fibrous, collagenous joints

Question 36

What pathology occurs when premature suture formation arises?

Answer 36

Craniosytosis

Question 37

The metopic suture closes by what age?

Answer 37

7 years old

Question 38

The formation of sutures occurs between what two structures?

Answer 38

2 osteogenic fronts

Question 39

The most common osteogenic fronts are derived from which developmental components?

Answer 39

Neural crest + mesoderm | different osteogenic fronts

Question 40

Which two signalling centres are important for suture formation?

Answer 40

Periosteum | Dura mater

Question 41

Which of the two signalling centres is more important?

Answer 41

Dura mater

Question 42

What are the 3 reasons that has led us to believe the dura mater is more important?

Answer 42

1) Mammalian skulls show more closed suture pattern internally (dural side). 2) Dural transplants affect development, whereas periosteal transplants don't. 3) More substrate molecules in dura mater.

Question 43

Which paper found these 3 findings?

Answer 43

Miura et al., 2009

Question 44

What age-related pattern occurs with sutures?

Answer 44

Begin thin and straight-edged. Become more complex and interdigitated.

Question 45

What are the findings from Jaslow et al., 1990 in regards to suture mechanics?

Answer 45

Sutures are able to absorb more IMPACT energy than bone. Sutures do, however, have lower bending strength than bone. Both of these do INCREASE with increased interdigitation.

Question 46

Therefore, what are two main roles of sutures?

Answer 46

1) Increase impact energy capacity (harder to fracture) | 2) Enable high biting forces (bending / compressive)

Question 47

Which two studies were shown to relate level of interdigitation to biting forces?

Answer 47

1) Moss, 1961 - removal of rat temporalis = less interdigitation. 2) Byron et al., 2004 - compared WT to GDF8 (hypermuscular) mice which had greater masseter + temporalis muscle, thus GREATER BITE FORCE.

Question 48

What two findings were made from Byron et al. 2004?

Answer 48

Suture deformation was significantly increased. Breaking strength was no different.

Question 49

How do parietal foramina at the obelion alter suture mechanics? Who did this mathematical model?

Answer 49

Parietal foramina form strain sinks to unload tension away from the line of sutures. Zollikofer and Weissman, 2011

Question 50

Describe Khonsari et al, 2013's hypothesis of suture mechanics from their model.

Answer 50

1) Begin with parallel borders. 2) External force pulls collagen fibres of which have various sites of origin. 3) Osteoblasts thought to migrate along length of collagen fibres 4) Creates preferential bone deposition sites. 5) Areas without osteoblast migration also shown to have greater osteoclast action (greater bone resorption)

Question 51

Khonsari et al., 2013 also concluded about bone 'growth' as a result from bone deposition lines / growth lines - what did he find?

Answer 51

Deposition lines were closer together at concavities and further apart at convexities of suture formation.

Question 52

High complex interdigitations can result in the formation of what structure? Most commonly found where?

Answer 52

Wormian bones Lambdoid suture.

Question 53

What homeobox gene has been shown to be important for branchial (pharygneal) arch development?

Answer 53

DIx5

Question 54

K/o of DIx5 results in what phenotypes?

Answer 54

Defects in craniofacial structures (e.g. ears, nose, mandible, calvaria). ALSO die shortly after birth.

Question 55

Which study shows DIx5 regulation on branchial arches?

Answer 55

Depew et al., 1999