How many bones are there in the skull?
22 (excl. ossicles of the ear)
What are the components of the skull?
- Mandible
- (Neuro)Cranium: made up of vault and base
- Viscerocranium
What are the bones of the cranium?
- frontal
- parietal (2x)
- temporal(2x)
- occipital (2x)
- ethmoid
- sphenoid
What are the facial bones of the skull?
- maxilla (2x)
- zygoma (2x)
- nasal (2x)
- lacrimal (2x)
- vomer
- inferior conchae (2x)
- palatine (2x)
- mandible
What are sutures in the skull?
fibrous joints permitting little or no movement.
What are the 2 openings in the skulls of newborns called? When do they close?
- anterior fontanelle (closes between 18-24 months of age)
- posterior fontanelle (closes during the first 2-3 months)
What are the skull sutures called?
- coronal suture
- sagittal suture
- lambdoid suture
Are the fontanelles easy to damage?
- no, contrary to popular belief
- there is tough fibrous tissue
What is one of the “functions” of the fontanelles?
- the skull bones have to move as the baby passes through the birth canal
- this is aided by the fact that the bones are not fused.
What are the intersections of the coronal sutures called?
- bregma (coronal and sagittal)
- lambda (sagittal and lambdoid)
Which bone is the external acoustic meatus located in?
Temporal bone
What is the inion?
- It is a protrusion on the posterior part of the skull.
- It is bigger in males than it is in females
What are the occipital condyles?
- They sit on the C1 vertebra
- allow nodding of head
What are the parts of the base of the skull?
- anterior cranial fossa
- middel cranial fossa
- posterior cranial fossa
what sits in the posterior cranial fossa?
Cerebellum
What is ‘ventral’ in neuroanatomy?
inferior
What are the main parts of the anterior cranial fossa?
- orbital part of the frontal bone
- spehnoid
- cribriform plate containing foramina
note: there are 2 depressions in the frontal lobe because it sits in the orbital part of the frontal bone where the eyes are, bone is curved because eyes are underneath.
What bones make up the middle cranial fossa?
- sphenoid bone
- temporal bone
- parietal bone
- foramina
Where is the foramen magnum located?
in the posterior cranial fossa
What bones make up the posterior cranial fossa?
- occipital bone
- temporal bone
- pariteal bone
- foramen magnum
- other foramina
Approximately, in what order are the cranial nerves positioned?
From 1 to 12 from rostral to caudal
What passes through the cribriform plate?
- olfactory nerve fibres
- ‘‘cribriform’’ = lat. ‘‘perforated’’ (cribrum = sieve)
What passes through the optic canal?
- Optic nerve (including central artery of retina)
- ophthalmic artery
What passes through the superior orbital fissure?
- Oculomotor (III)
- trochlear (IV)
- ophthalmic div. of V (V1)
- abducent (VI)
- sup ophthalmic vein
What passes through the foramen rotundum?
- maxillary division of V (V2)
What passes through the foramen ovale?
- mandibular division of V (V3)
What passes through the foramen lacerum; spehnopetrosal fissure?
- internal carotid artery
What passes through the foramen spinosum?
- Middle meningeal artery & vein
What passes through the carotid canal, internal aperture?
- internal carotid artery
What passes through the internal acoustic meatus?
- facial (VII)
- vestibulocochlear (VIII)
- labyrinthine artery
What passes through the jugular foramen?
- Glossopharyngeal (IX)
- Vagus (X)
- Accessory n (XI)
- sigmoid sinus → int jugular v
What passes through the hypoglossal canal?
- Hypoglossal nerve (XII)
What passes through the foramen magnum?
- Vertebral arteries
- medulla of brain
- spinal roots of accessory nerve
What are the layers of meninges?
- dura mater
- arachnoid mater
- pia mater
What are the qualities of the dura mater?
- thick
- inelastic
- 2 layers (meningeal and periosteal)
What are the qualities of the arachnoid mater?
- elastic
- spider like projections
What are the qualities of Pia mater?
- innermost
- thin
- delicate layer
What space is filled with CSF?
the subarachnoid space
What are the differences regarding epidural space in the brain and in the vertebral column?
- lack of epidural space in the brain
- large epidural space in the vertebral column
-> correct?
What happens as the meninges exit through the foramen magnum?
- the outermost layer is lost, it fuses with the skull
- inner layer (meningeal) of dura continues down the vertebral column
What is the purpose of dural folds?
- prevent movement of the brain
- provide spaces where blood can drain back into the venous system.
Where does the inner layer of the dura mater peel away?
e. g.
- down the longitudinal fissure
- provide spaces where blood can drain back into the venous system
What is the falx cerebra?
- main dural fold
- sickle shaped double layer
- at the top: superior sagittal sinus
What is the superior sagittal sinus?
- runs along the midline on the superior part of the brain
- where veins drain into the venous system to drain into the jugular veins
- it is penetrated by the arachnoid mater so that the CSF can be reabsorbed into the venous system before the jugular
What is the downside of the sheets?
- if there is a space occupying lesion (e.g. tumor, blood, oedema, cyst) in any compartment it can raise IC pressure and lead to herniation of part of the brain
Subfalcine herniation
not usually clinically significant
Uncal herniation
- affects midbrain
=> unconsciousness
Tonsillar herniation
- affects medulla
=> cardiorespiratory failure
Blood supply to the meninges
- rich blood supply
- Middle meningeal artery (MMA) inside the cranial cavity, supplies the meninges
MMA
- middle meningeal artery
- branches off of the maxillary artery which itself branches off of the external carotid
- runs along the pterion -> if that is fractured a large epidural bleed could occur
Pterion
- region where the frontal, parietal, temporal, and sphenoid bones join together
- fragile, thin bone
- if this area is fractured a large epidural bleed with disastrous consequences could occur
Why can infections outside (e.g. scalp) sometimes get into the cranial cavity?
- there are veins that traverse to outside of the skull to the cranial cavity
- some parts of skull and face drain not via the system external to the cranial cavity but internal to the cranial cavity
=> infections on the outside can sometimes get inside the cranial cavity
Confluence of sinuses
- ## connecting point of the superior sagittal sinus, straight sinus, and occipital sinus
Cavernous sinus
- clinically relevant because bleeds in the cavernous sinus can affect many cranial nerves
