Session 3 Flashcards
What is the neurocranium?
- The portion of the skull that completely covers the brain
- 8 bones
- Consists of calvaria, cranial floor, cranial cavity
What is the viscerocranium?
- Facial skeleton and jaw
- 14 bones
What type of ossification forms the neurocranium?
- Vault bones (skull cap) form by intramembranous ossification
- Cranial floor forms by endochondral ossification
What type of ossification forms the viscerocranium?
- Endochondral ossification
- Structures develop from the pharyngeal arches (1&2)
What are the names given to important osteological features of the bones of the skull?
- Fossae - shallow depressions or hollows
- Canals - bony tunnels
- Foramina - round(ish) holes
- Fissures - narrow slits
Why does the cranial floor contain many foramina, fissures and canals?
- To allow cranial nerves and blood vessels to enter and exit the neurocranium
What is a suture?
- Tough fibrous joint between the bones of the skull
What feature of the calvaria makes it strong?
- 2 layers of compact bone separated by a layer of spongey bone (diploe)
- Trilaminar arrangement
- Strength but lightweight
Which bones make up the calvaria?
- Frontal bone - forms part of roof of orbit
- Parietal bones - a pair
- Sphenoid bone - only greater wing can be seen from outside of skull
- Temporal bone - mastoid process
- Occipital bone - condyles articulate with C1 vertebra
What is a metopic suture?
- When fusion of the frontal bones fails
- Leaves a suture
- Don’t interpret as a fracture
What are the joints of the calvaria?
- Coronal suture between frontal bone and parietal bone
- Sagittal suture between paired parietal bones
- Lambdoid suture between parietal bones and occipital bone
What is the bregma?
- The intersection between the coronal suture and the sagittal suture
What is the lambda?
- The intersection between the sagittal suture and the lambdoid suture
What is the clinical relevance of the bregma and lambda?
- Relate to areas in foetal skull that remain membranous for up to 2 years
- Sutures aren’t fully ossified, allowing bones to grow as brain develops
What are fontanelles?
- Large unossified membranous gaps between flat bones of calvaria
- Allow for alteration of skull size and shape during childbirth
- Allows brain to grow
Why is the anterior fontanelle clinically useful when examining newborns and infants?
- Inspection and gentle palpation of anterior fontanelle
- Used to assess intracranial pressure
- Fontanelle bulges when pressure is high
- Used to assess state of hydration
- Fontanelle is sunken when dehydrated
- Must also assess how well/unwell infant appears and other sings/symptoms
What ‘shrink-wraps’ each individual skull bone?
- Periosteum
- Covers surfaces of outer and inner table of skull bones
- Strongly adhered to bone edges at suture line
- Continuous through suture and onto inner table of same bone
Why is the periosteum clinically important in haemorrhages?
- Specific shape of haemorrhage indicates blood vessel and type of haemorrhage
- Periosteum is really strongly adhered at sutures but blood can strip it away from inner table of bone at all other points
- This means that extra-dural haemorrhages have a lentiform shape
What forms the cranial floor?
- 3 bowl- shaped depressions
- Anterior, middle and posterior cranial fossae
- Seat different parts of brain and associated structures
- Made up of numerous bones
- Numerous foramina, canals and fissures
Which bones form the anterior cranial floor?
- Frontal bone
- Ethmoid bone
- Sphenoid bone
Outline the features of the ethmoid bone
- Superiorly has a sharp pointy bony prominence called crista galli
- Cribriform plate is flat and rectangular
- Contains many cribriform foramina through which olfactory nerves pass
- Perpendicular plate helps form part of nasal septum inferiorly
- Contains air filled cavities called paranasal air sinuses
Outline the features of the sphenoid bone
- Lesser wings form posterior part of anterior cranial fossa
- Greater wings form part of vault and middle cranial fossa
- Sella turcica
- Pituitary fossa, where pituitary gland sits, found in centre of sella turcica
Outline the features of the temporal bone
- Squamous part - extensive round part
- Zygomatic process helps to form shape of cheek
- Mastoid process acts as attachment for sternocleidomastoid
- Very superior edge of petrous bone forms boundary between middle cranial fossa and posterior cranial fossa
What are the holes in the sphenoid bone?
- Superior orbital fissure - transmits lots of different nerves, communicates with orbit
- Optic canal - transmits optic nerve
- Foramen rotundum - transmits maxillary division of trigeminal nerve (Vb)
- Foramen ovale - transmits mandibular division of trigeminal nerve (Vc)
- Foramen lacerum - filled with cartilage
- Foramen spinosum - transmits middle meningeal artery
- Carotid canal - transmits internal carotid artery