2 - Functional Anatomy of Cranial Sutures Flashcards
What type of joint is a cranial suture?
Fibrous synarthrotic joints
The skull is formed from two types of bone - what are they both called?
1) Endochondral bones
2) Dermal bones
How does endochrondral bone develop?
From cartilaginous precursors.
How does dermal bone develop?
Ossifies directly from mesenchyme.
What groups of bones form the dermal bone subset?
Bones of the face
Bones of the cranial vault
What groups of bones form the endochondral group?
Higher laryngeal skeleton
Cranial base bones
What two developmental tissue origins does the skull form bone from?
Neural crest tissue
Mesoderm
What parts of the skull are derived from mesoderm?
Brain case
cranial vault + floor
What parts of the skull are derived from neural crest tissue?
Facial skeleton
Upper laryngeal skeleton
What are the 3 developmental parts of the skull?
1) Chondrocranium
2) Splanchnocranium
3) Dermatocranium
The chondrocranium is involved in the development of bone associated with which skull feature?
Bones involved with special senses
The dermatocranium is involved functionally with the development of which skull bones?
What is the function?
Cranial vault + facial skeleton
Mastication
What are the 3 developmental contributions of the chondrocranium?
1) 3 pairs of cartilaginous precursors
2) Capsules for sensory organs
3) Occipital cartilages
What are the 3 pairs of cartilaginous precursors?
1) Prechordal
2) Hypophyseal
3) Parachordal
What structure is the splanchocranium associated with?
Pharyngeal arches
How many pharyngeal arches did humans used to have?
How many do they now have?
6
Now have 5.
What direction do the pharyngeal arches form?
Cranio-caudal succession.
What pharyngeal arch is no longer present?
No. 5
What are the 4 parts to each pharyngeal arch?
1) Ectoderm (outside)
2) Mesenchymal core
3) Endoderm (inside)
4) Cartilaginous skeletal element
Where does the cartilaginous skeletal element form from?
Neural crest tissue
What are the 3 possible fates of this skeletal element within the pharyngeal arches?
1) Ossify into bone
2) Stay as cartilage
3) Regress by parturition (act as a scaffold)
What day does the first pharyngeal arch form?
Day 22
The first pharyngeal arch gives rise to two prominences, what are they called?
Maxillary prominence (Palatopterygoquadrate)
Mandibular prominence (Meckel’s cartilage)
What 2 bony structures does the maxillary prominence give rise to?
Maxilla
Palate
What bone does the mandibular arch give rise to?
Mandible
What muscles does the first pharyngeal arch also give rise to?
Muscles of mastication
In the formation of the mandible, what cartilage is used as a template / scaffold but does NOT contribute directly to its formation?
Meckel’s cartilage
in mandibular prominence
What two bones does Meckel’s cartilage give rise to?
What two cartilages does Meckel’s cartilage give rise to?
Incus
Malleus
Sphenomandibular ligament.
Anterior ligament of malleus.
What ossification process is used in the formation of the mandible?
Perichondral ossification (out-to-in)
Give 3 examples of composite bones?
1) Sphenoid
2) Temporal
3) Occipital
What bones make up the temporal bone?
(Dermatocranium)
- Tympanic
- Squamosal
(Chondrocranium)
- Petromastoid
(Splanchnocranium)
- Styloid
What evolutionary features of the skull can be found before birth?
1) Orbits fully sized
2) Otic capsule fully developed
3) Negative allometry
What changes occur to the skull following birth?
1) Braincase volume increases
2) Facial height increases
3) Positive allometry
What are 2 functions of fontanelles?
1) Ease of parturition
2) Permits brain growth
What type of joints are fontanelles?
Fibrous, collagenous joints
What pathology occurs when premature suture formation arises?
Craniosytosis
The metopic suture closes by what age?
7 years old
The formation of sutures occurs between what two structures?
2 osteogenic fronts
The most common osteogenic fronts are derived from which developmental components?
Neural crest + mesoderm
different osteogenic fronts
Which two signalling centres are important for suture formation?
Periosteum
Dura mater
Which of the two signalling centres is more important?
Dura mater
What are the 3 reasons that has led us to believe the dura mater is more important?
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.
Which paper found these 3 findings?
Miura et al., 2009
What age-related pattern occurs with sutures?
Begin thin and straight-edged.
Become more complex and interdigitated.
What are the findings from Jaslow et al., 1990 in regards to suture mechanics?
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.
Therefore, what are two main roles of sutures?
1) Increase impact energy capacity (harder to fracture)
2) Enable high biting forces (bending / compressive)
Which two studies were shown to relate level of interdigitation to biting forces?
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.
What two findings were made from Byron et al. 2004?
Suture deformation was significantly increased.
Breaking strength was no different.
How do parietal foramina at the obelion alter suture mechanics?
Who did this mathematical model?
Parietal foramina form strain sinks to unload tension away from the line of sutures.
Zollikofer and Weissman, 2011
Describe Khonsari et al, 2013’s hypothesis of suture mechanics from their model.
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)
Khonsari et al., 2013 also concluded about bone ‘growth’ as a result from bone deposition lines / growth lines - what did he find?
Deposition lines were closer together at concavities and further apart at convexities of suture formation.
High complex interdigitations can result in the formation of what structure?
Most commonly found where?
Wormian bones
Lambdoid suture.
What homeobox gene has been shown to be important for branchial (pharygneal) arch development?
DIx5
K/o of DIx5 results in what phenotypes?
Defects in craniofacial structures (e.g. ears, nose, mandible, calvaria).
ALSO die shortly after birth.
Which study shows DIx5 regulation on branchial arches?
Depew et al., 1999
