3.1.1 Osteology of the Skull

Question 1

What are the two main parts of the skull?

Answer 1

Viscerocranium- face
Neurocranium-Brain

Question 2

What bones make up the neck?

Answer 2

Cervical Vertebrae C1-C7
Atlas C1 (1 earth)
Axis C2 (2 axis x and y stfu about z)

Question 3

What are some characteristics about cervical vertebrae? (look back at msk)

Answer 3

• Triangluar vertebral foramina
• Transverse foramina (konduit for vertebral artery, vein and sympathetic nerves)
• Bifid spinous process (not C7)

Question 4

What are some characteristics about the Atlas?

Answer 4

C1
* No vertebral body
* No spinous process
* Lateral masses
* Odontoid Peg/ Dens articulates with anterior part
* Has grooves for C1 spinal nerve posteriorly

Question 5

What are some characteristics about the Axis?

Answer 5

C2
* Odontoid peg (dens)
* Articulates with C1
* Forms the atlantoaxial joint

Question 6

How many bones are in the skull?

Answer 6

22

Question 7

What are some important osteological features of the skull?

Answer 7

• Shallow depressions or hollows (fossae)
• Bony tunnels (canal)
• Holes- round-ish=foramina and Narrow slits=fissures

Question 8

What does the neurocranium consist of?

Answer 8

8 Bones- Encases/protects brain

Calvaria (skull cap/vault), cranial floor (base) and cranial cavity

Question 9

How do vault bones begin?

Answer 9

Begin as membranes, ossifies via intramembranous ossification

Question 10

How do floor/base bones begin?

Answer 10

Cartilage, ossifies via endochondrial ossification

Question 11

How does the viscerocranium begin?

Answer 11

14 bones
* Bones begin as membrane or cartilage and ossify
* Structures (most) develop from pharyngeal arches (1&2)

Question 12

Label the bones

Answer 12

Question 13

Label the sutures

Answer 13

Bregma is where coronal and sagital suture meet

Lambdoid is where lambdoid and sagittal sutures meet

Question 14

Why are sutures so irregular?

Answer 14

Serrated to prevent movement in newbornes, areas not fully ossified at this point

Question 15

What are fontanelles?

Answer 15

Large areas of unossified membranous gaps between flat bones of calvaria

Question 16

What do fontanelles do?

Answer 16

Allows alteration of skull size during child birth

Permits growth of infant brain

Question 17

When do fontanelles fuse?

Answer 17

Anterior- 18-24 months
Posterior- 1-3 months

Question 18

What is craniosynostosis?

Answer 18

Rare condition in which there is easly fusion of fontanelles and sutures

Brain is compressed and unable to grow, can lead to deformity and neurological problems if not treated

Need to break bone and allow it to re-fuse

Question 19

What is the shape of the anterior fontanelle?

Answer 19

Slightly convex

Question 20

How can the anterior fontanelle be used clinically?

Answer 20

Inspection and gentle palpation to assess intracranial pressure and hydration

Bulging=high ICP
Sunken=dehydrated

Question 21

How is the cross-section of the calvaria arranged?

Answer 21

Trilaminar
Outer table- compact
Diploe- spongy bone
Inner table- compact

Question 22

What does a trilaminar arrangement do?

Answer 22

Confers protective strength without adding significant weight

Question 23

What covers each bone of the calvaria?

Answer 23

Periosteum- covers outer and inner table

Continuous through suture and onto outer table of bone

Question 24

What does the periosteum cause in intracranial exdural haemorrhages?

Answer 24

Distinct lemon shape on CT of extradural haemorrhage

This occurs as periosteal dura is strong around suture lines and edges of bone, as bleeding occurs within periosteal dura is stripped from inner table but the periosteal dura is particularly strongly adhered at the sutures so it causes this distinctive shape as the blood cannot expand further