Osteology and Radiology (Skull) Flashcards
What 2 bones make up the skull?
Cranium + Mandible
In an adult what is the only movable joint?
Temporomandibular Joint
The points of interlocking bone in the skull are known as what? What type of joint is this?
Fibrous joints called sutures
Give 3 functions of the skull
1) Encloses and protects the brain and the special sense organs (eyes, ears, tongue, nose)
2) Creates specialised environment in which the brain thrives
3) Site for attachments of muscles (externally) and meninges (internally- periosteal layer of dura mater)
The thickness of cranium is variable, give 2 thick areas and 1 thin area
Thick areas: Occipital and frontal bones
Thin areas: Pterion
What is the Pterion?
Which important artery is found below the Pterion and why is this important?
Pterion: parital, frontal, temporal and sphenoid
Artery found beneath pterion is the MMA and can be damaged during head injury leading to a extradural haematoma
The cranium has a tri-lamina bony structure, what are the 3 layers?
Give 2 features of each
2 plates of compact bone (thick plates):
- Outer and Inner plate
- Resilient
1 middle layer of spongy bone:
- Diploe layer (cancellous bony tissue)
- Reduces weight of cranium
Label the bones of the skull
Label the image of the skull below
The Mandible is a bilateral bony structure, what are the 2 parts and how are they joined?
Formed by the union of R & L mandibles
Joined by a midline fibrous joint → Mental Symphisis
Label the following parts of the mandible:
- Condylar Process
- Coronoid Process
- Ramus
- Angle
- Body
- Mental foramen
- Alveolar arch
Which part of the mandible is the portion that
a) articulates with skull
b) non-articulating portion
c) located at the internal ridge
d) where nerves exit into chin to supply the skin of the face
a) condylar Process → articulates with skull
b) coronoid Process → non-articulating portion
c) alveolar Process → internal ridge
d) mental foramen
What feature of the bony edges of the skull aid in interlocking
Bony edges are serrated which allows the bones to interlock, making it less likely for them to easily unlock when force is applied one direction
List the 4 sutures of the skull and label them on the image below
What are the 3 sections where the sutures join? Label 2 of them on the image below
Sutures: Coronal, Sagittal, Lambdoid, Squamous
Join: Bregma, Lambda, Pterion
How can the cranial floor (cranial fossa) be divided?
Each division contains unique openings , list which CN exits through each
Divided into 3 fossae
1) Anterior Fossa: CN I and II (CN II foramen is on the junction between anterior and middle fossa)
2) Middle Fossa: CN II - VI
3) Posterior Fossa: CNs VII- XII
Cranial Nerves are numbered?
CNI – CN XII: from how they exit the cranial base from an anterior to posterior direction
What 3 bones make up the anterior cranial fossa?
What 2 ‘holes’ are found here and what CN passes here?
Bones:
- Frontal
- Ethmoid
- Sphenoid
Holes:
- Olfactory foramina in cribriform plate (CNI)
- Optic canal (CNII)
What 2 bones make up the Middle Cranial Fossa?
What 4 ‘holes’ are found here and what CN passes here?
Bones:
- Sphenoid
- Temporal
Holes:
- Superior orbital fissure (CN III, IV, VI, V1)
- Foramen rotundum (CN V2) (part of trigeminal nerve)
- Foramen ovale (CN V3) (other part of trigeminal nerve)
- Foramen spinosum (MMA)
What 4 bones make up the Posterior Cranial Fossa?
What 4 ‘holes’ are found here and what CN passes here?
Bones:
- Temporal
- Occipital
- Bits of the Sphenoid
- Bits of the Parietal
Holes:
- Foramen magnum
- Internal acoustic meatus (CN VII, VIII)
- Jugular foramen (CN IX,X,XI)
- Hypoglossalcanal (CN XII)
Label the bones below
Palatine plate
Sphenoid
Temporal
Occipital
What is the major opening of the skull?
Foramen magnum
Through what structure does the facial nerve exit the skull?
Stylomastoid Foramen
Give 2 functions of the foramina of the cranial base
1) Decrease weight of skull
2) Passageway for structures to enter/exit skull
Give 3 things that may enter/exit the skull through the cranial base (2 normal, 1 pathological)
1) Nerves:
- sensory (enter)/motor (exit)
- SNS fibres (enters)/PNS outflow (exits)
2) Blood vessels:
- arterial supply to brain and meninges (enter)
- venous blood (enters/exits)
3) Infections (enters/exits)
Why is the cranial base is at risk of fracture?
Large number of foramina make skull floor weak
What anterior cranial bone forms the upper border of the orbital margins and roof of orbit?
Frontal
What bone ‘nested’ in the midline allows passage of Olfactory nerve (CN I) fibres from nasal mucosa directly to the brain?
What may a fracture of this bone lead too?
Ethmoid
Fractures here can lead to damage to CN I resulting in loss of smell (may be irreversible)
What bone is ‘bat-shaped’ and sits at the upper aspect of nasal cavity?
This bone has alot of holes, what artery and nerve ‘thread through these
Sphenoid
Optic nerve & Internal Carotid Artery threads through this bone
List the 2 wings of the Sphenoid bone
What 2 things are located in the central body of this bone?
Greater wing and Lesser wing
Central Body:
- Sphenoidal sinus found here
- Pituitary gland sits on top of this bone (in the Sella Turcica)
What 4 important landmarks are found on the Internal surface of the parietal bone?
What is the importance of the external surface?
Internal:
1) Grooves of MMA
2) Sagittal sulcus
3) Granular pits (from CSF Valves)
4) Grooves for the Sigmoid Sinus
External: attachments of muscles
What is the function of the Temporal bone?
What CN passes through this bone?
Role in protecting organs of hearing & balance
Allows passage of Facial nerve (CN VII)
The temporal bone can be divided into 6 parts.
Label 1-5 shown on the image below and state the 6th that is not shown
1) Squamous
2) Mastoid
3) Tympanic
4) Styloid process
5) Zygomatic process
6) Petrous (stony –very hard)
What is the organ of hearing and balance indicated on the image below?
What 2 nerves passes through here?
Petrous part of the Temporal bone
1) Facial nerve (VII) passes through this bone to get to face
2) Vestibulocochlear Nerve (CN VIII) passes through here also
What the 4 parts of the occipital bone and what structure are they arranged around:
4 parts arranged around foramen magnum:
Squamous: posterior part of vault
x2 Condylar (2 Condyles, R and L, at edges of foramen magnum)
Basilar: anterior part of foramen magnum
Give 3 differences between and baby vs adult skull
1) Baby’s ratio of size of head to rest of body is greater
2) Sutures are open in a baby and fused in an adult
3) Baby’s ratio of neurocranium to viscerocranium is 8:1, adult is 2:1
Why are babies sutures not fused?
For increased mobility to aid in getting head out of pelvis at birth (‘moulding’)
What are the 2 fontanelles in a neonate and state when each closes?
What is the clinical significance of these?
Posterior fontanelle: closes up first
Anterior fontanelle: closes at around 10-24months
At birth if a baby is sick the Anterior fontanelle can be used to determine:
If a baby is dehydrated: the fontanelle will be sunk in (Concave)
If a baby has increase pressure in skull or hydrocephalus: the fontanelle will be bulging (Convex)
What can occur due to Pterion Injury?
Can be life-threatening as the pterion overlies the MMA hence fracture can results in extradural haemorrhage
Give 2 signs of a ‘base of the skull’ fracture
1) Battles sign
2) Periorbital ecchymosis (racoon/panda eyes)
Give 2 other types of skull fractures
Linear or Depressed Fracture
What is a growing fracture?
Fracture remains unfused/unhealed as child’s skull grows
What is a ping pong fracture?
A depressed skull fracture of the infant skull caused by inner buckling of the calvarium
It is seen in newborns because of the soft and resilient nature of their bones
What is an orbital blowout fracture and what can this type of fracture result in?
Most often caused by a punch in the eye
Pushes the eyeball backwards and pushes through bone located below the eye socket.
Below this bone is the maxillary sinus and thus this fracture can result in problems with muscles that supply eye.
