Skull Overview and Applied Anatomy of Face and Jaws Flashcards
What plane is used to compare skulls?
Frankfurt horizontal (FH) plane
What 3 points define the Frankfurt horizontal plane?
- Right and left porion points (located at top of each external acoustic meatus)
- Left orbitale (located at bottom of left orbit)
Using FH, skulls are viewed from 5 standard perspectives. What are these perspectives?
- Norma verticalis (from above)
- Norma lateralis (from side)
- Norma occipitalis (from behind)
- Norma frontalis (from front)
- Norma basilaris (from below)
What gives the skull its strength despite being lightweight?
It’s large number of bones.
how many bones does the skull have at least?
23 (including the hyoid)
What does the large number of bones in the skull also contribute to?
It’s versatility.
What are the 3 benefits of having more joints between bones in the skull?
- More joints between bones enables babies with bigger heads to be born.
- More joints facilitate complex growth patterns.
- More joints increase the resilience of the structure and so reduces the danger of fractures assuming catastrophic proportions.
What is the role of the skull?
To support and protect the brain and organs of special sense as well as housing the first part of the respiratory and alimentary tracts.
The skull can be divided into 2 parts, what are these 2 parts?
- The neurocranium (braincase)
2. The viscerocranium
What does the neurocranium consist of?
- A base
- A vault whose side walls and roof (calvaria) complete the bony covering
What is the role of the neurocranium
To support & protect the brain
What does the viscerocranium consist of?
- Consists of most of face, hyoid and larynx
- The upper part forms the orbits and nose
- The lower part, together with the mandible, constitutes the jaws
What is the role of the viscerocranium?
Aids breathing and eating
What are the 2 types of Neurocranium?
- Membranous neurocranium
2. Cartilaginous neurocranium
What is the membranous neurocranium also known as?
Dermatocranium
What is the cartilaginous neurocranium also known as?
Chondrocranium
What makes up the membranous neurocranium?
The flat bones of skull cap
eg frontal, parietal
What makes up the cartilaginous neurocranium?
The bones of base of skull
eg ethmoid, sphenoid
What is the membranous neurocranium formed by?
Formed by intramembranous ossification
What is the cartilaginous neurocranium formed by?
Formed by endochondral ossification
Is the membrane bone more protective or more supportive?
Membrane bone is more protective
Is the endochondral bone more protective or more supportive?
Endochondral bone is more supportive
Name 5 design features of the adult skull that combine to increase chances of survival to reproductive age.
- Lightness
- Strength
- Keeping airway open
- Warming & humidifying air breathed in through nose
- Supporting muscles involved in chewing & swallowing
Name a design feature of the neonatal skull that increases chance of survival?
How is there conflict for the mother in this design feature?
Bigger head: this means bigger brain and therefore better survival chances for baby (better developed protective reflexes).
Foetal size too big for mothers pelvis- pelvic disproportion- mother and child can die
Name 2 design features of the neonatal skull that facilitate birth?
- the babies head is DEFORMABLE (“moulding” within the birth canal)
- Minimal development of inessential parts (eg. small jaws - liquid diet - no chewing, small nose - no sense of smell)
What anatomical features give the neonatal skull its deformability?
- wide sutures
- fontanelles
- thin, deformable bones of the neurocranium
What happens to the sutures in the skull as you become older?
They become interdigitated.
What is the Fontanelle?
An area of membrane that has not yet turned bone- known as a soft spot- facilitates moulding to reduce size of head during child birth.
What are the flat bones of the dermatocranium made from?
The flat bones of the dermatocranium are made from an outer and an inner plate of thin compact bone
How many layers of compact bone are there?
Name these layers.
3 layers
- Outer cortex or outer compact bone
- Diploe
- Inner cortex or inner compact bone
What is found interspersed between these layers of compact bone ?
Diploe
What process do all three layers form by?
Intramembranous ossification
What are 3 characteristics of diploe?
- Light
- Strong
- Flexible
How does the Dermatocranium restrict crack propagation?
By consisting of multiple smaller bones as to one big bone. This stops the crack from spreading further from the point of injury.
What do the joints in the skull act as?
“crack stoppers” preventing fracture propagation- wont travel through diploe or inner cortex- will just remain on outer cortex.
When looking at traumatic forces to the facial skeleton,
what happens as a result of a blow to the mid-face (maxillary region)?
- The bones crumple rather than remaining intact to be driven towards and through the base of the skull.
- Le Fort pattern fractures separate face from the base of skull rather than damaging base of skull.
When looking at traumatic forces to the facial skeleton,
what happens as a result of a blow to the lower face (mandible)?
- Dense bone so can absorb forces to a certain extent.
- Will fracture itself rather than be driven via its condyle through the base of the skull.
The face doesn’t crumple everytime we chew. What stops this from happening?
Due to buttresses (thicken area of bone in the facial skeleton)
The maxilla is made of thin bone and is hollow; due to this what must it do when masticatory forces are applied to prevent it from fracturing?
it has to dissipate biting (occlusal) forces away from itself and onto the neurocranium via three pathways (the “buttress system”) or it might fracture
The maxilla is a light bone with THREE strengthened areas through which the forces are channelled to the whole skull. The strengthened parts are called CRANIO-FACIAL BUTTRESSES. Name these cranio-facial buttresses.
- Frontonasal
- Zygomatic
- Pterygoid
How many Le Fort Fractures of the Facial Skeleton are there?
What is each fracture?
Rank them in order of severity.
Le Fort I - when the alveolar maxilla separates from rest of face. This is the least serious fracture.
Le Fort II - entirety of midface separates.
Le Fort III - complete separation of viscerocranium to neurocranium. This is the most serious fracture.
What are the two points that define the Le Fort III fracture and what does this fracture divided?
- Above the orbits
- Below the ears
This fracture divides the bones of the cranial vault
from the bones of the face.
What is the most common mandibular fracture?
The most common mandibular fracture is separation of the condyle.
What is the second most common fracture?
Separation from the body.
What is the least common fracture?
Fracture of the ramus
