Osteology of the skull Flashcards
the functions of the skull?
• Protection of the brain
• House special sense organs
• Creates optimal environment for thew brain
• Houses upper respiratory and digestive tract
• Has muscle and meninges attachments
What are the divisions of the skull
• Cranium and the mandible make the skull
• Cranium is made from the cranium vault (calvaria) and the facial skeleton (viscerocranium)
• Only mobile joint in the skull the TMJ
• The other joints are fused/can’t move called sutures
What is viscerocranium and neurocranium?
• viscerocranium is the facial skeleton.
○ ‘viscero-‘ means organs = houses the organs of the upper respiratory and digestive tract
• Neurocranium is the cranium vault (calvaria). It houses the brain and its associated anatomical structures
○ The bones of the Neurocranium make the cranium vault
○ Neurocranium is divided into the base (where the brain sits) and the skull cap (covers the brain)
What are the ossifications of the skull?
• Cranium subdivisions= cranial base, cranial vault/calvaria and facial skeleton
• Cranial base/chondrocranium is endochondral
• endochondral=placement of hyaline cartilage first then the hyaline cartilage is replaced by bone
• Cranial vault/calvaria is intermembranous
• Facial skeleton is intermembranous
• intermembranous=formation of bony tissue directly from mesenchymal cells
What is the basic embryology of facial bones?
• Endochondral ossification- chondrocranium is the cranial base
• chondrocranium is endochondral. endochondral=placement of hyaline cartilage first then the hyaline cartilage is replaced by bone
• Intermembranous ossification-calvaria from head. intermembranous=formation of bony tissue directly from mesenchymal cells
○ Viscerocranium from the phalangeal arches which derives from mesenchymal (neural crest) cells –bone develops from sheets of mesenchymal tissue
• Most bones form by Intermembranous ossification except the mandible (both sides) and inferior. Mandible has both intermembranous and endochondral ossification nasal concha
How many bones are in the skull and how many in the neurocranium and the visceraocranium?
• 22 discrete bones (some are the same on both sides)
• Neurocranium/calvaria=8 bones
• viscerocranium /facial skeleton=14 bones
What are the Cranial bones?
• Neurocranium/calvaria=8 bones
• Frontal (1)
• Partial (2)
• Temnportal (2)
• Occipital (1)
• Sphenoid (1)
• Ethmoid (1)
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What are the facial bones?
• viscerocranium /facial skeleton=14 bones
• Maxilla (2)
• Lacrima (2)
• Nasal (2)
• Vomer (1)
• Palatine (2)
• zygomatic (2)
• inferior nasal concha (2)
• Mandible (1)
• Lacrimal bone is where nasal lacrimal duct sits on
• Palatine bone makes up parts of the hard pallet
What types of joints are in the skull?
• The only mobile join is the temporomandibular join (TMJ)
• Cranial bones are head together with a fibrous suture
• Fibrous sutures are joints that can’t not be moved
• All other joints in the skull are immovable and symphysis=a
fibrocartilaginous fusion between two bones
• Main joints are the coronal, sagittal, lambdoid and squamous
• Called the Pterion where frontal, lacteal and lacrimal bone meet
• Directly under need you have the meningeal artery
• Very thin
• Suture bones are Rare and usually don’t indicate disease
unless there are a lot of them
• New born skull is mostly unfused
• New born have fontanelles
• Most bones in babies fuse in the 1st year of life. Allows growth and development of the skull in the first 2 years. Some sutures may only form in the adolescent to allow further growth
○ Allow head to squash during child birth and protects the brain during child birth (smaller head to deliver)
○ Cleidocranial dysostosis=no clavicle, informed clavicle, sutures form late or don’t form at all
○ Anterior fontanelle>bregma (Fontanelle is the hole where the bregma or lambda suture would be)
○ Posterior fontanelle>lambda
○ Merotopic sutures usually disappear
What is the thickness of the cranial bones?
• Mixture of flat and irregular bones
• Flat bones of the calvaria/cranial vault and offer protection
• Has 3 layers: most inner cortical layer is thin, middle diploe is a spongy layer and outer cortical layer is thick.
• The outer most and inner most layer are compact bone and the middle bone is inner bone.
• Compact bone is dense
• Spongy bone is the site if haematosis (red bone marrow creates blood cells). Spongy bone and paranasal sinus (frontal, maxillary, ethmoid and sphenoid) makes the bone lighter
Tell me about where the bones meet
• Called the Pterion where frontal, lacteal and lacrimal bone meet
• Directly under need you have the meningeal artery
• Very thin
• Suture bones are Rare and usually don’t indicate disease unless there are a lot of them
• bregma is where the partial and optical bones meet- is also slightly weaker
tell me about the sphenoid bone
• Creates the lateral walls and base of the middle cranial fossae
• Important as there are many blood vessels and nerves running though it
• The sphenoid is an irregular bone
What are the cranial cavities?
• Paranasal sinuses
• Nasal cavity
• Cranial vault/cavity
• Ocular orbit
• Auditory canal
• Oral cavity
Tell me about the cranial vault
• Cranial vault/cavity or intercranial cavity
• Largest cavity
• Where the brain sits
• Subdivided by dural reflections
• Drain is continuous with spinal cord. Spinal cord passes though the foremen magnum
Tell me about the foramina?
• Let structures in and out the cranium e.g. blood vessels and nerves
• Cranial nerves must leave the skull
• Blood vessels enter and leave the skull via the bony conducts
• Foramina may look different from different angles (e.g. top and bottom of the cranium base)
• Tiny foramen in the bones allow blood to pass into the skull but can easily spread infections
What are the cranial fossae?
• Fossae are like depressions or dips in the skull (not holes)
• The cranial base has 3 fossae
• Anterior fossa
• Middle fossa
• Posterior fossa
• When you look at the skull you can’t see the full cranium as the viscerocranium gets in the way
Tell me about the zygomatic bone
• Zygoma
• Bilateral (on both sides)
• Forms the zygomatic arch (with the temporal bone)
• Has temporal process with articulates
• Has zygomatic process of temporal bone
• Inferolateral margin of orbit
• Zygomatic dome forms interior part of the orbit
• Forms the cheek Bone
• Zygomatic arch = temporal process of zygomatic bone
• Lots of nerves originate from this area
Tell me about the maxillae
• Paired maxillae bones, right and left maxilla
• Contains the maxillary sinus
• Forms the majority of the upper face skeleton
• Gives rise to the orbit, nasal cavity, face, cheek bones
• Forms the upper jaw
• Parts=body and 4 bony processes
• Process= frontal, zygomatic, palatine and alveolar
• Maxillae provides lateral wall of orbital cavity and interior wall
• Forms anterior part of the hard pallet
Tell me about the palatine bone
• Paired bone (2 present)
• Forms posterior part of the hard pallet
• Horizontal plate=posterior part of pallet
• Perpendicular plate= vertical, lateral wall of the nasal cavity
• Pyramidal, orbital and sphenoid process
Tell me about the vomer
• Unpaired bone (only 1 present)
• Vomer is the posterior inferior part of the nasal septum
• Articulates with perpendicular part of the ethmoid bone
• Midsagittal line
• Other articulations: sphenoid, maxilla, nasal septal carriage and palatine bones
• Forms the poster inferior part of the nasal septum
Tell me about the inferior nasal concha
• Aka inferior turbinate bone
• Most inferior concha is formed as a separate bone whereas the superior and middle is formed from the ethmoid bone
• Creates a larger surface area to warm and humidify the air
Tell me about the nasal and lacrimal bones
• Both are bilateral and paired
• Nasal bone- makes the bridge of the nose. Inferior portion forms the superior margin of the nasal aperture
• Lacrimal-very thin and fragile. Reticular and forms the medial walls of orbital
Tell me about the mandible
• Forms as 2 bones but fuses at the mandibular symphysis therefore 2 bone
• Unpaired bone
• Forms lower jaw
• Articulates with the temporal bone at the TMJ
• Parts=body, ramus, coronoid process, condylar process and alveolar process (alveolar= teeth)
• Attachments of muscles of mastication/ floor of the mouth
• Has important foramen for neurovascular structures
• Mandible is considered one bone but joins to getter at the mandibular synthesis
• Ramus is the flat bits that form the lateral side (where massager is sitting)
• Mandibular canal/foeman allows one nerves to run and inverse the lower teeth
Tell me about the viscerocranium fractures
• Nose fractures are most common as it is exposed
• Left zygomatic is more likely to be fractured as most people are right handed
• Mandible can also be fractures
• Le fort facture classifications. Fractures on the midface=3. separation if all or some facial bones from skull base=1. 1>3 in severity. Involves pterygomaxillary separation.
• Type 3 can be fatal as skull base separates from skull cap and can cause CFS to leak
• Type 1-horistanal maxillary fractures e.g. separation of teeth from upper face
• Type 2- pyramidal e.g. fracture that passes though alveolar ridge
• Type 3 - transverse e.g. passes though structure. Whole maxilla, zygomatic bones and orbits separating from neurocranium
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