Osteology

Question 0

Describe the function of each of the skull bones

Answer 0

Frontal- forms the forehead, floor of cranial cavity and roof of orbit
- articulates nasal, zymoatic, lacrimal, ethmoid and sphenoid bones

Zygoma- sits inferolaterally to orbits
- articulates with frontal, sphenoid, temporal and maxillae

Temporal- has 6 regions: squamous, mastoid process, tympanic, styloid process, zygomatic process and petrous part

Occipital- condylar processes articulate with vertebral column

Sphenoid- butterfly shape with greater and lesser wings, with pterygoid plate

Ethmoid- midline of anterior cranial fossa

• forms cribriform plate, crista galli, ethmoid bulla and air cells (important in sense of smell)
• anosmia can result from a fracture

Maxillae- large part of upper facial skeleton and is fixed to cranial base

Mandible- moveable due to TMJ
- formed by fusion of two bones at mental symphysis

Question 1

Discuss the general make up of the skull

Answer 1

Skull = cranium and mandible

Cranium consists of calvaria (frontal, parietal, occipital, and ethmoid bones)
Base of skull consists of sphenoid and temporal bones

Bones are flat, made up of two layers of compact bone (inner and outer plates) with a layer of spongy bone (diploe) between

Connected by sutures

• sagittal connects the two parietal bones
• coronal connects the frontal to parietal bones (creates anterior - brogma fontanelle)
• lambdoid connects occipital and parietal (creates posterior-lambda fontanelle)

Question 2

What are the foramen of the skull?

Answer 2

Foramen magnum - vertebral arteries and anterior/posterior spinal arteries plus medulla oblongata, and spinal fibres of CN XI

Foramen ovale - accessory meningeal artery and meningeal branch of CN V3

Foramen spinosum - middle meningeal artery and meningeal branch of CN V3

Foramen lacerum - artery and nerve of pterygoid canal

Carotid canal -

Jugular foramen - internal jugular vein, sigmoid sinus and inferior petrossal sinus plus CN IX, X, XI

Emissary foramen - emissary veins

Question 3

Describe the make up of the brain linings

Answer 3

Cranium (outermost)
Extramural space or epidural space in spinal cord (potential)
Double layered dura mater
Subdural space (potential)
Arachnoid mater
Subarachnoid space (true space containing blood vessels and CSF)
Brain

Question 4

What is the function of the CSF?

Answer 4

Bathes brain
Cushions brain
Provides metabolic substrates (nutrition)
Removes waste products

Question 5

List common sites of skull fractures

Answer 5

1. Squamous temporal bone and parietal bone
2. Foramen magnum
3. Anterior cranial fossa (cribriform plate and roof of orbits)
4. Middle cranial fossa (thin bones, multiple foramina)
5. Posterior cranial fossa (between mastoid and ducal sinuses)

Question 6

Why is the pteroin an important feature of the skull?

Answer 6

It is the junction between many bones (parietal, sphenoid, temporal, frontal) producing a ‘H’ suture

Common site for fractures, complicated by fact middle meningeal artery lies between (haemorrhage)

Question 7

Describe features of the cervical spine

Answer 7

• transverse foramen for verbal arteries
• pyramid shaped vertebral foramen
• small vertebral body
• bifida processes (except C1, C2 and C7)

C1: atlas, ring shaped bone which supports the skull (Atlanta-occipital joint)
C2: axis, dens on which C1 rotates. Held in place by transverse ligaments of atlas
C3-6: short bifid process, vertebral foramen get bigger down the spine
C6: had carotid tubercles (anterior tubercle). Carotid arteries can be compressed against these to control bleeding
C7: long spinous process (vertebra prominens). Still have small transverse foramen but vertebral arteries don’t pass through them