The Skull Flashcards
How many bones is the skull made up of?
22 (some paired, some unpaired)
What are most of the bones of the skull connected by? What is the 1 exception to this?
- Fibrous sutures (i.e. joint that is non moveable)
- 1 exception: temporomandibular joints (one found on either side i.e. paired) –> these are synovial
What 2 groups can the bones of the skull be considered as?
- Those of the cranium
- Those of the face
What is the cranium?
- Formed by the superior aspect of the skull
- It encloses and protects the brain, meninges, and cerebral vasculature
Anatomically, what can the cranium be divided into?
A roof and a base
What is the cranial roof comprised of?
frontal, occipital and two parietal bones
What is this bone? Is it paired or unpaired?
Frontal bone - unpaired
What underlies the frontal bone?
The frontal lobe of the brain
How does the frontal bone contribute to the orbital cavity?
Forms the roof
What bone is this? Is it paired or unpaired?
Parietal bone - paired (one on each side with a suture in between them)
What suture fuses the 2 parietal bones to each other?
The sagittal suture
What is the name of this suture?
Coronal suture
What does the coronal suture fuse?
Fuses the frontal bone with the two parietal bones
What is this bone? Is it paired or unpaired?
Zygomatic bone (or cheek bone) - paired
How does the zygomatic bone contribute to the orbital cavity?
Forms the lateral wall
What is this bone? Is it paired or unpaired?
The maxilla - paired (suture in the middle)
How does the maxilla contribute to the orbital cavity?
Form floor
What else does the maxilla comprise?
Part of the upper jaw and hard palate
What is this bone? Is it paired or unpaired?
Lacrimal bone - paired
How does the lacrimal bone contribute to the orbital cavity?
Forms part of medial aspect
What is this bone found just posteriorly to the lacrimal bone? Is it paired or unpaired?
Ethmoid bone - unpaired
How does the ethmoid bone contribute to the orbital cavity?
Lateral walls of ethmoid form the medial walls of orbital cavity
How does the ethmoid bone contribute to the nasal cavity?
Forms the roof of the nasal cavity
What does the ethmoid bone articulate with inferiorly?
The vomer bone
What forms the superior part of the nasal septum?
The perpendicular plate of the ethmoid bone
What forms the inferior part of the nasal septum?
The vomer
What bone is this? Is it paired?
Inferior nasal concha - paired
What is this bone? Is it paired or unpaired?
The sphenoid bone - unpaired (one, single large bone)
How does the sphenoid bone contribute to the orbital cavity?
Forms the posterior aspect
Shape of sphenoid bone
What bone is this? Is it unpaired or paired?
The mandible
What does the mandible hold?
The lower teeth
What is this bone? Is it paired or unpaired?
The temporal bone - paired
What does the mandible articulate with posteriorly? At what joint?
The temporal bone at the temporomandibular joint
What bones form the cranial base?
6 bones: frontal, sphenoid, ethmoid, occipital, parietal and temporal.
What are the facial bones?
- Zygomatic (2)
- Lacrimal (2)
- Nasal (2)
- Inferior nasal conchae (2)
- Palatine (2)
- Maxilla (2)
- Vomer
- Mandible
What are the paranasal sinuses?
Hollow cavities found in the skull
What are the names of the paranasal sinuses?
- Frontal
- Ethmoidal
- Maxillary
- Sphenoidal
How are the paranasal sinuses named?
According to which bone they are found in
Are the paranasal sinuses paired or unpaired?
Paired - even if they are found in a bone that is unpaired
What is the function of the paranasal sinuses?
- Lighten the weight of the skull
- Filter and humidy air
- Resonate voice
- Drain fluid into specific meatuses in the nasal cavity
What are the nasal conchae? How many are there?
Conchae are curved shelves of bone projecting out of lateral walls of nasal cavity. There are 3; inferior, middle and superior
How does the inferior concha differ from the superior and middle conchae?
- Inferior concha is a bone on its own (facial bone)
- Superior and middle conchae form part of the ethmoid bone
What is found beneath each concha?
Meatuses (pathways for air to flow)
What meatus is found beneath the superior concha?
The superior meatus
What meatus is found beneath the middle concha?
The middle meatus
What meatus is found beneath the inferior concha?
The inferior meatus
What sinuses drain into the superior meatus?
The sphenoidal and ethmoidal sinuses
SES: sphenoidal ethmoidal superior (meatus)
What sinuses drain into the middle meatus?
The maxillary and frontal sinuses
MFM: maxillary frontal middle (meatus)
What drains into the inferior meatus?
The nasolacrimal duct
Function of the nasolacrimal duct?
Drains tears from eyes to nasal cavity
What gland is found above the sphenoid sinus?
The pituitary gland
What bone is the pituitary gland situated in?
The sphenoid bone
What is this projection of the temporal bone called?
The mastoid process
What is this projection found just anteriorly to the mastoid process?
Styloid process
What is this canal?
External auditory opening / external acoustic canal
Function of external auditory opening?
Connects external ear with middle ear
What is the external auditory opening covered by?
A tympanic membrane (eardrum)
What is this area of the temporal bone called?
Zygomatic process of the temporal bone
What does the zygomatic process connect the temporal bone with?
The zygomatic bone
What muscle attaches to the zygomatic process?
The masseter muscles
At what joint does the temporal bone articulate with the mandible?
At the temporomandibular joint of the jaw
What forms the temporomandibular joint?
Fossa of the temporal bone called the mandibular fossa and the condyle of the mandible
Temporal bone and its parts diagram
What does the mandible form?
It forms the lower jaw and acts as a receptacle for the lower teeth.
What does the mandible articulate with on either side?
with the temporal bone, forming the temporomandibular joint
What is this part of the mandible called?
Mandibular condyle
What is this part of the mandible called?
Coronoid process of the mandible
What is this part of the mandible called?
The ramus of the mandible
What is this part of the mandible called?
The angle of the mandible
What meets at the angle of the mandible?
The mandible consists of a horizontal body (anteriorly) and two vertical rami (posteriorly). The body and the rami meet on each side at the angle of the mandible.
What is the pterion?
The region where the frontal, parietal, temporal and sphenoid bones join, located on the side of the skull just behind the temple
What is this bone?
Occipital
What does the occipital bone articulate with anteriorly? What suture is involved?
The parietal bones via the lambdoid suture
What doe the lambdoid suture connect?
Fuses the occipital bone to the two parietal bones
What are these 2 protrusions of the occipital bone?
Occipital condyles
What do the occipital condyles sit on top of?
1st cervical vertebrae
What is found just deep to the pterion?
Middle meningeal artery and its branches
Why is the pterion clinically important?
Thin area of bone - fractures can injury the middle meningeal artery causing blood to accumulate between the skull and the dura mater - forming an extradural haematoma
What is the dura mater?
Outermost layer of the meninges
What are these grooves on the inside of the skull formed by?
The middle meningeal artery
Branches of the middle meningeal artery and its branches diagram
Xray of an extradural haematoma
What can an extradural haematoma lead to?
can cause compression of local brain structures and a rise in intracranial pressure
What can noticed regarding the skull of newborns?
Bones are not quite fused together
What are fontanelles?
Membranous areas (soft spots) where bones haven’t yet fused together
What is the purpose of fontanelles?
- To allow deformation during birth through the birth canal
- To accomodate brain growth after birth
Why are newborns more prone to ear infections?
The external auditory canal is more shallow and short
In newborns, the temporal bone is very underdeveloped: the styloid process is well developed but the mastoid process is not. What stimulates the mastoid process to develop?
As newborns develop the ability to move their neck and hold it upright, these muscles that attach to the mastoid process create mechanical pressure which stimulates bone growth
E.g. sternocleidomastoid muscle
What is a foramen?
an opening that allows the passage of structures from one region to another
What is the purpose of the cranial formaina?
In the skull base, there are numerous foramina that transmit cranial nerves, blood vessels and other structures
The floor of the cranial cavity is divided into 3 distinct depressions. What are these known as?
- Anterior cranial fossa
- Middle cranial fossa
- Posterior cranial fossa
What does each cranial fossa accomodate?
A different part of the brain
What does the anterior cranial fossa accomodate?
the anteroinferior portions of the frontal lobes of the brain
What are these ridges called?
Sphenoid ridges
What do the sphenoid ridges separate?
The anterior cranial fossa from the middle cranial fossa
What fossa is found behind the sphenoid ridges?
The middle cranial fossa
What does the middle cranial fossa accomodate?
- Pituitary gland
- Two lateral parts of the temporal lobes
What separates the middle cranial fossa from the posterior cranial fossa?
The petrous part of the temporal bone
What is the petrous part of the temporal bone?
- a wedge shaped mass of bone located between the sphenoid and occipital bones
- is the most medial part of the temporal bone
- is the landmark dividing the middle and posterior cranial fossae from each other.
What is this part of the temporal bone?
Squamous part
Describe the inner surface of the temporal bone
More rough –> this is the petrous area
What does the posterior cranial fossa accomodate?
Cerebellum and brainstem
What is this called? What bone is it part of?
Crista galli - part of the ethmoid bone
In which cranial fossa can the crista galli be seen as an important landmark?
The anterior cranial fossa
What is the crista galli an important attachment point for?
The dura mater
What is the crista galli?
An upward projection of ethmoid bone (remember is seen on the floor of the cranial cavity)
What is found either side of the crista galli?
The cribriform plate
What are these 2 foramina (one on either side)?
The optic canal
What bone are the optic canals a part of?
The sphenoid bone
What elongated foramen / fissure is being pointed to?
Superior orbital fissure
What foramen is being pointed to?
Foramen rotundum
What foramen is being pointed to?
Foramen ovale
What foramen is being pointed to?
Foramen spinosum
What acronym can be used to remember foramen rotundum, foramen ovale and foramen spinosum?
ROS
What foramen is this? Found medially to ROS
Foramen lacerum
Why is the foramen lacerum not a natural foramen in the living?
Is covered by layer of cartilage (which dissolves in cadaver)
What foramen is this? What bone is it found in?
Internal auditory canal/meatus found in the petrous temporal bone
What foramen is being pointed to?
Jugular foramen
What is this large single foramen?
Foramen magnum
What bone is foramen magnum found in?
Occipital bone
What is this foramen called?
Hypoglossal canal
What is this fossa? What sits here?
Pituitary fossa where the pituitary gland sits
N.B. also known as the hypophysial fossa
What do the holes in the cribriform plate allow the passage of?
CN1 - olfactory nerve
What does the optic canal allow the passage of?
CNII - optic nerve
What does the superior orbital fissure allow the passage of?
CNIII - oculomotor nerve
CNIV - trochlear nerve
CNV1 - 1st division of trigeminal nerve - opthalmic nerve
CNVI - abducens nerve
What does foramen rotundum allow the passage of?
CNV2 - 2nd branch of the trigeminal nerve –> maxillary nerve
What does the foramen ovale allow the passage of?
CNV3 - 3rd branch of trigeminal nerve –> mandibular nerve
What does foramen spinosum allow the passage of?
Entry into the cranial cavity of the middle meningeal artery
What does foramen lacerum allow the passage of?
Nothing
What does the internal auditory canal allow the passage of?
- CNVII –> facial nerve
- CNVIII –> vestibulocochlear nerve
What does the jugular foramen allow the passage of?
- Internal jugular vein
- CNIX - glosopharyngeal nerve
- CNX - vagus nerve
- CNXI - accessory nerve
What does the hypoglossal canal allow the passage of?
CNXII - hypoglossal nerve
What does the foramen magnum allow the passage of?
Spinal cord
Which part of the maxilla forms part of the hard palate?
The horizontal process of the maxilla
What other bone contributes to the hard palate?
Palatine bones
Where are the palatine bone situated?
(seen in orange) situated at rear of oral cavity
What bone is being pointed to? (pink)
Vomer
How does the vomer contribute to the nasal septum?
Forms posterior aspect of nasal septum
What bone is being pointed to? (yellow)
Sphenoid bone
What bony ridge of the sphenoid bone is being pointed to?
Medial pterygoid plate
What bony ridge of the sphenoid bone is being pointed to?
Lateral pterygoid plate
What is highlighted?
Mastoid process
What is the stylomastoid foramen? Where is it found? What cranial nerve does it transmit?
Foramen is between the styloid and mastoid processes of the temporal bone. It is the termination of the facial canal, and transmits the facial nerve and stylomastoid artery.
Where is the carotid canal found? What passes through here?
passageway in the temporal bone through which the internal carotid artery enters the middle cranial fossa from the neck.
Passage of hypoglossal canal photo
