2. Introduction to the skull

The skull is divided into 2 regions:  

Neurocranium / Viscerocranium

Function of Neurocranium

Allow neurovascular passage between intracranial & extracranial anatomy 

There are 2 sets of paired bones in the neurocranium:

parietal / temporal bones

Frontal /1

Parietal /2

Sphenoid / 1

Ethmoid / 1

Temporal / 2

Occipital / 1

What is the ‘dorsal (top) part of the skull ’?

calvarium

What is the ‘ventral (bottom) part of the skull‘?

Cranial base

What is the calvarium?

dorsal part of the skull

How many paired bones are in the viscerocranium?

12

How many bones are in the viscerocranium?

14

Vomer /1

Zygomatic / 2

Palatine / 2

Nasal / 2

Lacrimal / 2

Inferior nasal concha / 2

Maxilla

At birth, the skull comprised of how many bones?

45

Size of skull increases with the development of _______?

the mandible and maxilla

What are cranial suture?

bony articulations that exist between the bones of the skull

What are cranial sutures separated by?

separated only by fibrous tissue comprised mainly of cartilage

What do cranial suture start off as?

They start as a series of ossification centres around a foetus’ brain

What do ossification centres allow?

allows for the rapid growth of the brain

When do ossification centres become suture?

As brain growth slows

What are the major sutures of the skull?

coronal / sagittal / lambdoid / squamosal

Sagittal suture

coronal suture

Squamous suture

Lamboid suture

occipitomastoid suture

Parietomastoid suture

What does the sagittal suture connect?

2 parietal bones and intersects with the frontal and occipital bone

What does the coronal suture connect?

frontal bone and the 2 parietals

Usually, which suture obliterates first?

Sagittal suture

What is the order of the sutures that obliterate from first to last? (must be in order)

Sagittal / coronal / lambdoid

What is the metopic suture?

divides the frontal bone in infants

When does the metopic suture fuse?

3-9 months

When does the metopic suture obliterate?

by age 7

What is metopism?

When the metopic suture line is retained into adulthood

What % of adult population has metopism?

~6%

What does fossa mean?

pit, cavity or depression

What are the 3 fossa’s found in the base of the skull?

Anterior / middle / posterior cranial fossa

What is the anterior cranial fossa comprised of?

frontal bone, ethmoid bone and sphenoid bone

What does the anterior cranial fossa accommodates?

frontal lobe

What is the shallowest of the cranial fossa?

Anterior cranial fossa

Ethmoid bone

important bone as the cribriform plate allows the transmission of the olfactory fibres

Ethmoid bone

Cribriform plate

Lamina orbitalis

Ethmoid air cells

What is the middle cranial fossa comprised of?

sphenoid bone and the 2 temporal bones

What does the middle cranial fossa accommodates?

pituitary gland and the temporal lobes of the brain

Where does the pituitary gland sit in the middle cranial fossa?

sits in a depression in the sphenoid bone - sella turcica

sella turcica

What is the posterior cranial fossa comprised of?

occipital and the 2 temporal bones

What does the posterior cranial fossa accommodate?

the brain stem and cerebellum

Which is the deepest of the cranial fossa?

Posterior cranial fossa

What is the temporal fossa comprised of?

parietal, temporal, frontal and sphenoid bones

What muscle occupies the temporal fossa?

temporalis muscle

What is the temporal fossa?

shallow depression on the temporal region of the skull

What are the 2 fossae that sit behind the zygomatica arch

Infratemporal / Pterygopalatine fossae

Foramen

An opening, hole or passage usually through a bone

Fissure

A slit like groove

Basic function of Foramen and fissures

Transmit major nerves and blood vessels

What are the 6 Major foramina?

Supraorbital / Optic / magnum / rotundum / cribriform plate / Internal acoustic meatus

Supraorbital foramen:

it allows passage of the supraorbital vein, artery, and nerve into the orbit.

Supraorbital foramen location:

frontal bone

Optic foramen:

it allows the passage of the ophthalmic artery and nerve from the optic canal into the orbit.

Optic foramen location:

located in the sphenoid

Foramen magnum:

it allows the passage of the spinal and vertebral arteries and the spinal cord to pass from the skull into the vertebral column.

Foramen magnum location:

occipital bone

Foramina of cribriform plate:

it allows the passage of the olfactory nerve.

Foramina of cribriform plate location:

ethmoid bone

Foramen rotundum:

it allows passage of the maxillary nerve.

Foramen rotundum location:

sphenoid bone

Internal acoustic meatus:

it allows passage of the vestibulocochlear and facial nerves

Internal acoustic meatus location:

temporal bone

Superior orbital fissure:

it transmits many nerves including the oculomotor and nasociliary nerves, as well as the superior ophthalmic vein.

Where is the superior orbital fissure located?

Sphenoid bone

Inferior orbital fissure:

transmits the zygomatic branch of the maxillary nerve, the inferior ophthalmic vein, and sympathetic nerves

What is biparietal osteodystrophy?

Symmetrical, bilateral thinning of the parietal bones

What is the cause of biparietal osteodystrophy?

Cause unknown but possibly related to osteoporosis

What is the diploe?

Spongy inner bone

What is Craniosynostosis?

A birth defect where the bones in a baby’s fuse together too early

What is the name of the condition: A birth defect where the bones in a baby’s fuse together too early

Craniosynostosis

What does Craniosynostosis result in?

cranial deformation

What is Hydrocephaly?

Caused by the buildup of CSF in ventricles deep within the brain.