Session 3 Flashcards

1
Q

What is the neurocranium?

A
  • The portion of the skull that completely covers the brain
  • 8 bones
  • Consists of calvaria, cranial floor, cranial cavity
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2
Q

What is the viscerocranium?

A
  • Facial skeleton and jaw
  • 14 bones
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3
Q

What type of ossification forms the neurocranium?

A
  • Vault bones (skull cap) form by intramembranous ossification
  • Cranial floor forms by endochondral ossification
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4
Q

What type of ossification forms the viscerocranium?

A
  • Endochondral ossification
  • Structures develop from the pharyngeal arches (1&2)
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5
Q

What are the names given to important osteological features of the bones of the skull?

A
  • Fossae - shallow depressions or hollows
  • Canals - bony tunnels
  • Foramina - round(ish) holes
  • Fissures - narrow slits
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6
Q

Why does the cranial floor contain many foramina, fissures and canals?

A
  • To allow cranial nerves and blood vessels to enter and exit the neurocranium
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7
Q

What is a suture?

A
  • Tough fibrous joint between the bones of the skull
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8
Q

What feature of the calvaria makes it strong?

A
  • 2 layers of compact bone separated by a layer of spongey bone (diploe)
  • Trilaminar arrangement
  • Strength but lightweight
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9
Q

Which bones make up the calvaria?

A
  • Frontal bone - forms part of roof of orbit
  • Parietal bones - a pair
  • Sphenoid bone - only greater wing can be seen from outside of skull
  • Temporal bone - mastoid process
  • Occipital bone - condyles articulate with C1 vertebra
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10
Q

What is a metopic suture?

A
  • When fusion of the frontal bones fails
  • Leaves a suture
  • Don’t interpret as a fracture
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11
Q

What are the joints of the calvaria?

A
  • Coronal suture between frontal bone and parietal bone
  • Sagittal suture between paired parietal bones
  • Lambdoid suture between parietal bones and occipital bone
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12
Q

What is the bregma?

A
  • The intersection between the coronal suture and the sagittal suture
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13
Q

What is the lambda?

A
  • The intersection between the sagittal suture and the lambdoid suture
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14
Q

What is the clinical relevance of the bregma and lambda?

A
  • Relate to areas in foetal skull that remain membranous for up to 2 years
  • Sutures aren’t fully ossified, allowing bones to grow as brain develops
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15
Q

What are fontanelles?

A
  • Large unossified membranous gaps between flat bones of calvaria
  • Allow for alteration of skull size and shape during childbirth
  • Allows brain to grow
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16
Q

Why is the anterior fontanelle clinically useful when examining newborns and infants?

A
  • Inspection and gentle palpation of anterior fontanelle
  • Used to assess intracranial pressure
  • Fontanelle bulges when pressure is high
  • Used to assess state of hydration
  • Fontanelle is sunken when dehydrated
  • Must also assess how well/unwell infant appears and other sings/symptoms
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17
Q

What ‘shrink-wraps’ each individual skull bone?

A
  • Periosteum
  • Covers surfaces of outer and inner table of skull bones
  • Strongly adhered to bone edges at suture line
  • Continuous through suture and onto inner table of same bone
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18
Q

Why is the periosteum clinically important in haemorrhages?

A
  • Specific shape of haemorrhage indicates blood vessel and type of haemorrhage
  • Periosteum is really strongly adhered at sutures but blood can strip it away from inner table of bone at all other points
  • This means that extra-dural haemorrhages have a lentiform shape
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19
Q

What forms the cranial floor?

A
  • 3 bowl- shaped depressions
  • Anterior, middle and posterior cranial fossae
  • Seat different parts of brain and associated structures
  • Made up of numerous bones
  • Numerous foramina, canals and fissures
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20
Q

Which bones form the anterior cranial floor?

A
  • Frontal bone
  • Ethmoid bone
  • Sphenoid bone
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21
Q

Outline the features of the ethmoid bone

A
  • Superiorly has a sharp pointy bony prominence called crista galli
  • Cribriform plate is flat and rectangular
  • Contains many cribriform foramina through which olfactory nerves pass
  • Perpendicular plate helps form part of nasal septum inferiorly
  • Contains air filled cavities called paranasal air sinuses
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22
Q

Outline the features of the sphenoid bone

A
  • Lesser wings form posterior part of anterior cranial fossa
  • Greater wings form part of vault and middle cranial fossa
  • Sella turcica
  • Pituitary fossa, where pituitary gland sits, found in centre of sella turcica
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23
Q

Outline the features of the temporal bone

A
  • Squamous part - extensive round part
  • Zygomatic process helps to form shape of cheek
  • Mastoid process acts as attachment for sternocleidomastoid
  • Very superior edge of petrous bone forms boundary between middle cranial fossa and posterior cranial fossa
24
Q

What are the holes in the sphenoid bone?

A
  • Superior orbital fissure - transmits lots of different nerves, communicates with orbit
  • Optic canal - transmits optic nerve
  • Foramen rotundum - transmits maxillary division of trigeminal nerve (Vb)
  • Foramen ovale - transmits mandibular division of trigeminal nerve (Vc)
  • Foramen lacerum - filled with cartilage
  • Foramen spinosum - transmits middle meningeal artery
  • Carotid canal - transmits internal carotid artery
25
Why is the foramen lacerum not a true foramen?
- Arises due to a small gap between petrous part of temporal bone and sphenoid - Filled with cartilage and nothing of significance passes through it - Internal carotid artery passes over the top
26
Why is the petrous part of the temporal bone so important?
- Houses delicate middle and inner ear structures
27
Outline the features of the occipital bone
- External occipital protuberance can be palpated - Superior nuchal line - attachment for trapezius - Foramen magnum - brainstem passes through this
28
What is required to fracture the skull?
- Significant trauma and force - Resistance to fracture varies depending on thickness of cranial bones - Fractures carry risk of injury to intracranial structures
29
What are the different types of intracranial fracture?
- Linear - fairly straight, involves no bone displacement - Comminuted (multiple fracture lines) - fragments may or may not displace inwards towards the brain
30
What is the clinical relevance of the pterion?
- Pterion is intersection between frontal, parietal, sphenoid and temporal bones - Very thin, so very easily fractured - Middle meningeal artery lies directly beneath - Blows to lateral side of head can fracture bone in this area and injure artery lying immediately below - This causes an extra-dural haemorrhage
31
What happens if the ethmoid bone is fractured?
- Clear fluid may drip through nose - This is CSF
32
What is the specific sign of fractures of the orbital plates?
- Periorbital ecchymosis (panda/racoon eyes) - May take hours-days to develop
33
What are the specific signs of a middle cranial fossa fracture of the petrous bone?
- blood and CSF coming out of ear - Battle's sign (mastoid ecchymosis) - blood pooling in middle ear cavity
34
Which bones make up the facial skeleton?
- Zygomatic x2 - Maxilla - Nasal - Lacrimal - Mandible
35
Which facial bones are most commonly fractured?
- Nasal bones - Zygomatic bones and arches - Mandible - These are most prominent on the face
36
What types of X-ray might you use to look at facial fractures?
- Bucket handle view - looking at zygomatic arches - Panoramic radiograph (OPG) to look at mandible - Mandible normally has more than one fracture
37
Why are maxilla fractures concerning?
- The maxilla could fall backwards and occlude the airways - These fractures are rare
38
What is the temporomandibular joint?
- Articulation between temporal bone and mandible - Synovial hinge-type joint - Fibrocartilaginous disc divides joint into 2 synovial cavities - Innervated by auriculotemporal nerve - branch of mandibular division of trigeminal nerve (Vc)
39
What conditions can affect the TMJ?
- TMJ disorder - Dislocation - Arthritis
40
Outline the anatomy of the TMJ
- Articular surface of bones lined with fibrocartilage and do not come into direct contact - Separated by fibrocartilaginous disc - Divides joint into two synovial-lined cavities filled with synovial fluid - Stabilised by joint capsule and three extracapsular ligaments
41
What are the movements of the TMJ?
1. Hinge (rotational action) allowing opening and closing of jaw - inferior joint capsule 2. Gliding forward action - condyle slides onto articular tubercle - superior joint capsule 3. Simple retraction and protraction of mandible - gliding action at superior joint capsule
42
Which muscles elevate the mandible?
- Masseter - Temporalis - Medial pterygoid
43
Which muscles depress the mandible?
- Lateral pterygoid - Gravity - Platysma assisted by suprahyoid (against resistance)
44
Which muscles protract the mandible?
- Lateral pterygoid - Assisted by medial pterygoid
45
Which muscles retract the mandible?
- Posterior fibres of temporalis (inserts onto coronoid process of mandible)
46
What can cause TMJ dislocation?
- Facial trauma (especially when jaw is open) - Yawning
47
What happens as jaw dislocates?
- Jaw locks as joint fixes in open position - This is due to anterior dislocation of condyle over articular tubercle - Muscles of mastication contract - Keeps jaw locked in anterior displacement
48
What are the meninges?
- 3 membranous layers that surround and protect the brain and the spinal cord - Completely continuous around brain, brainstem, spinal cord - Pia mater, arachnoid mater, dura mater
49
Describe the pia mater
- Microscopic - Follows every dip and fold of the surface of the brain - Can't be peeled away from underlying tissue structure
50
Describe the arachnoid mater
- Pushed up against inner surface of dura mater - Doesn't extend into sulcae or lateral fissures - Delicate + translucent + fibrous layer
51
What makes up the leptomeninges?
- Pia mater and arachnoid mater - Meningitis affects this area
52
Describe the dura mater
- Really tough fibrous membrane
53
What is the subarachnoid space?
- The space between the arachnoid mater and the pia mater - Filled with CSF - this exerts pressure to keep 2 layers separated - Cerebral veins run through this space - Blood vessels entering through the base of the skull set up an arterial blood supply in this space - cerebral arteries arise from here
54
Which part of the skull does the dura fuse to?
- Periosteum lining inner table of skull bones
55
Why is the dura like 'two-ply' tissue?
- It has 2 layers while within the skull: 1. Periosteal - part against the inner table of bone 2. Meningeal - part adjacent to arachnoid mater - these 2 layers are closely adhered but there are areas where they separate
56
What does the separation of the layers of dura form?
- Dural folds - Dural venous sinuses