Control Lecture 2: The Skull

Question 1

What are the 22 bones of the skull? Note also whether these bones are paired or unpaired.

Answer 1

1. Frontal Bone (unpaired)
2. Zygomatic Bone (paired)
3. Lacrimal Bone (Paired)
4. Ethmoid Bone (unpaired)
5. Maxilla (Paired)
6. Mandible (Unpaired)
7. Vomer (Unpaired)
8. Inferior Nasal Concha (Paired)
9. Sphenoid bone (Unpaired)
10. Nasal Bone (Paired)
11. Temporal Bone (Paired)
12. Parietal Bone (Paired)
13. Occipital Bone (Unpaired)
14. Palatine `Bone (Paired)

Question 2

What is the coronal suture?

Answer 2

Dense, fibrous connective tissue joint that joins the parietal bones and the frontal bone.

Question 3

What contains the superior and middle concha?

Answer 3

Ethmoid bone

Question 4

What is the role of the sinuses?

Answer 4

The sinuses are paired. They may be found in unpaired sensed. There role is to:

- Filter and humidify air 
- Resonate voice
- Drain fluid into channels in the nasal cavities - meatus 
- Lighten the skull

Question 5

Where do the sphenoid sinuses and ethmoid air cells drain into?

Answer 5

Superior Meatus (SES)

Question 6

Where do the Maxillary sinuses and frontal sinuses drain?

Answer 6

Middle Meatus (MFM)

Question 7

What drains into the inferior meatus?

Answer 7

The Nasolacrimal Duct

Question 8

What is the mastoid process?

Answer 8

Temporal bone projection on each side

Question 9

What is the styloid process?

Answer 9

Sharp protrusion anterior to the mastoid process on the temporal bone.

Question 10

What is the role of the external auditory meatus?

Answer 10

Connects the external ear with the middle ear. It is covered in tympanic membrane.

Question 11

What is the role of zygomatic process of the temporal bone?

Answer 11

Attachment point for various muscles especially the master muscle.

Question 12

What type of joint is the temporal-mandibular joint?

Answer 12

Synovial joint - It is moveable.

Question 13

What are the landmarks on the mandible?

Answer 13

• Coronoid process of the mandible
• Condylar process of the mandible
• Mandibular notch
• Ramus
• Angle
• body

Question 14

Why is trauma to the Pterion dangerous?

Answer 14

The Pterion is the meeting point for the parietal bone, sphenoid bone, frontal bone and temporal bone. This is a particularly thin part of bone. Just deep to this region of bone is the middle meningeal artery and its branches. It supplies the dura matter. If it is fractured, this can be particularly dangerous. This can cause blood accumulation between the skull and dura matter. If we have blood accumulating outside the dura we can have an extradural haematoma/extra dural-haemorrahge. It puts pressure on the brain and can be very dangerous if not treated soon.

Question 15

What is the lambdoid suture?

Answer 15

Occipital bone - connects with the parietal bone by the lambdoid suture.

Question 16

What do the occipital condyles sit on top off?

Answer 16

The first cervical vertebrae

Question 17

What are the fontanelles?

Answer 17

In the skull of new-borns the bones are not yet fused. There are large membranous areas called the fontanelles. The bones do not fuses to allow:
- Deformation through birth
To accommodate brain growth postnatally

Question 18

Why are ear infections common in new-borne babies?

Answer 18

Their shorter, more horizontal eustachian tubes let bacteria and viruses find their way into the middle ear more easily. The tubes are also narrower, so more likely to get blocked.

Question 19

What are the 3 aspects of the cranial cavity?

Answer 19

The floor of the cranial cavity has 3 aspects:

- Sphenoid ridges sperate the anterior cranial fossa from the middle cranial fossa. The frontal lobe is found in the anterior fossa.
- In the middle cranial fossa we see the temporal lobes
- Dividing the middle cranial fossa from the posterior cranial fossa is the petrous temporal bones (the rough aspect). In the posterior cranial fossa we have the cerebellum and the brain stem.

Question 20

What passes through:

1. The Cribriform Plate
2. Optic canals on the sphenoid bones
3. Superior Orbital Fissure

Answer 20

1. Cranial Nerve I - Olfactory Nerve
2. Cranial Nerve II - Optic Nerve
3. Cranial Nerve III (Oculomotor Nerve), Cranial Nerve IV (Trochlear Nerve) and the first division of the Cranial Nerve V Trigeminal nerve (ophthalmic branch) and Cranial Nerve VI (Abducens Nerve).

Question 21

What vessels pass through ROS?

Answer 21

1. Foreman Rotundum - allows the passage of second passage of the Trigeminal nerve - the maxillary branch
2. Foreman Ovale - allows the passage of the third branch of the Trigeminal nerve - the mandibular branch
3. Foreman Spinosum - allows the passage into the cranial cavity of the middle meningeal artery

Question 22

What foreman is found medial to ROS?

Answer 22

Medial to ROS is foreman lacerum. There is one on each side. It has quite an irregularly shaped. In the living it is not a foreman as it is covered in a thin layer of cartilage.

Question 23

What canal does Cranial Nerve VII and Cranial Nerve VIII travel through?

Answer 23

The internal auditory canal - The facial nerve and Vestibocochlear nerve travel through here

Question 24

What nerves travel through the jugular Foreman?

Answer 24

Allows for the passage of the internal jugular vein, Cranial nerve IX (Glossopharyngeal Nerve), Cranial Nerve X (Vagus Nerve) and Cranial Nerve XI (Spinal accessory nerve).

Question 25

What passes through foreman magnum?

Answer 25

Important for the passage of the spinal cord.

Question 26

Where does cranial nerve XII travel through?

Answer 26

The hypoglossal canal found tucked under the occipital condyles.

Question 27

What are the flat plates of the sphenoid bone?

Answer 27

The sphenoid bone has two flat medial pterygoid plates and lateral pterygoid plates. These are important attachments for our muscles of mastication.

Question 28

What foreman can be found between the styloid process and the mastoid process?

Answer 28

Between the styloid process and the mastoid process is a foreman called the stylomastoid foreman. It allows the exit of the facial nerve - cranial nerve VII. It has an intracranial course.

Question 29

What is found medial to the stylomastoid foramen and what passes through it?

Answer 29

Medially to the stylomastoid foreman is the carotid canal. This allows entry of the internal carotid artery.

Question 30

What foreman cannot be seen from the base of the skull?

Answer 30

Foramen rotundum is not from the base of the skull but foreman ovule and foreman spinosum can be seen.