Skull and Cervical Spine: Anatomy and Imaging Flashcards
Name the main bones of the orbit.
Frontal Lacrimal Ethmoid Maxilla Zygomatic Sphenoid ➡Greater wing Palatine
Identify the structures which pass through the superior orbital fissure.
- Lacrimal nerve
- Frontal nerve
- Trochlear nerve
- Superior ophthalmic vein
- Nasociliar nerve
- Oculomotor nerve
- Abducens nerve
Identify the structures which pass through the inferior orbital fissure.
- Zygomatic branch of maxillary nerve
- Infraorbital nerve
- Inferior ophthalmic vein
- Sympathetic nerves
What is the skull ?
Cranium, bony skeleton of the head, including the mandible
What does the skull contain ?
Houses the brain, organs of special sense, upper part of respiratory and gastrointestinal system
How much movement is possible at the skull ?
Restricted movement only in relation to the mandible at the temporomandibular joint (TMJ, to open and close the mouth) and the atlanto-occipital joint
Identify the main functions of the skull.
- Protects the brain, brainstem, cranial nerves and vasculature
- Provides attachment for muscles
- Provides a framework for the head
- Gives us our identity as individuals
What types of bones make up the skull ?
Flat and irregular bones
Pneumatised bones
Define pneumatised bone, and give examples. What is their function ?
Bones with air spaces (air cells or sinuses) such as the frontal, temporal, sphenoid and ethmoid
Serve 2 functions in the skull; to reduce weight and add resonance to our voice
What is the difference between development and irregular bones ?
- Flat, smooth bones form by intramembranous ossification
* Irregular bones form by endochondral ossification
Identify the main divisions of the skull.
1) Neurocranium: Bony case of the brain including cranial meninges with a dome-like roof (calvaria/skullcap) and a floor (cranial base/basicranium)
2) Viscerocranium: Anterior part of cranium that consists of bones surrounding the oral cavity, nasal cavity and most of the orbit
How many bones does the skull contain ?
22 bones in the adult excluding the ossicles of the ear (28 with ossicles)
Identify the bones of the neurocranium. How many are there in total ?
8 in total
➡ Singular midline bones: Frontal Occipital Sphenoid Ethmoid
➡ Sets of bilateral paired bones:
Parietal x2
Temporal x2
Identify the bones of the viscerocranium. How many are there in total ?
15 irregular bones
➡ Singular midline bones:
Ethmoid
Vomer
Mandible
➡ Sets of bilateral paired bones: Nasal x2 Lacrimal x2 Zygomatic x2 Palatine x2 Maxillae x2 Inferior Nasal Conchae x2
What are the main features of the viscerocranium ?
Zygomatic arch, mandible and infratemporal fossa
What are the main features of the neurocranium ?
External acoustic meatus (opening), styloid and mastoid processes and temporal fossa
Identify the superior, inferior, posterior, anterior borders, and floor of the temporal fossa.
Superior and posterior borders: Superior and inferior temporal lines
Anterior border: Frontal process of zygomatic bone and zygomatic process of frontal bone
Inferior border: Infratemporal crest deep to zygomatic arch
Floor: Includes pterion
What is the pterion ?
- H-shaped junction of sutures
* Frontal, parietal, temporal, and greater wing of sphenoid bone meet here
What is the clinical significance of the pterion ?
Structurally weak (thin) area of the skull. Overlies anterior branch of the middle meningeal artery, so vulnerable, trauma can lead to extradural (epidural) hematoma
Describe the location of the pterion (in surface anatomy).
4cm superior to midpoint of zygomatic arch and 3cm posterior to frontal process of zygomatic bone.
What are the main components of the calvaria ?
4 flat bones (2x parietal, single frontal and occipital) fused by the coronal, sagittal and lambdoid sutures
What is the function of arachnoid granulations ?
Arachnoid granulations return CSF to the venous circulation.
Define Wormian bone.
Sutural, accessory
or Wormian bones, are msall islands of bone which may be seen within a cranial suture (most commonly observed in the lambdoid sutures)
Define suture. How much movement is allowed here ?
- Structurally, type of fibrous joint
* Functionally, limited or no movement (synarthrosis)
Define fontanelle. What is their function ?
“One of the membrane-covered spaces remaining at the junction of the sutures in the incompletely ossified skull of the fetus or infant, that fuse in the post-natal life”. Two of them, anterior and posterior fontanelle
Along with sutures, allow moulding of cranial shape during birth + post-natal growth of brain.
How soon do fontanelles close ?
• Posterior fontanelle closes 2 months post-birth
• Corners of frontal and
parietal bones fuse by 18 months (anterior fontanelle)
Which of the fontanelles is palpable ?
Anterior NOT
Posterior palpable
Identify the divisions of the trigeminal nerve, and the foramina they pass through.
Supraorbital nerve (branch of V1) (through supra-orbital notch)
Zygomatic branch of maxillary nerve (through infra-orbital foramen)
Inferior alveolar nerve (branch of V3) (through mental foramen)
Identify the craniometric points. What is their clinical significance ?
Asterion: Star shaped; located at junction of three sutures: parietomastoid, occipitomastoid, and lambdoid
Inion: Most prominent point of external occipital protuberance
Pterion: Junction of greater wing of sphenoid, squamous temporal, frontal, and parietal bones; overlies course of anterior division of middle meningeal artery
Nasion: Point on cranium where frontonasal and internasal sutures meet
Lambda: Point on calvaria at junction of lambdoid and sagittal sutures
Bregma: Point on calvaria at junction of coronal and sagittal sutures
Glabella: Smooth prominence; most marked in males; on frontal bones superior to root of nose; most anterior projecting part of forehead
Vertex: Superior point of neurocranium, in middle with cranium oriented in anatomical (orbitomeatal or Frankfort) plane
Important anatomical landmarks in radiology and surgery
Identify the main paranasal sinuses.
- Frontal
- Ethmoidal
- Sphenoid
- Maxillary
Where is the pterygoid plate located ?
Either of the two processes of the sphenoid bone, descending from the points of junction of the great wings and the body of the bone, and each consisting of a lateral and a medial plate.
Identify the main foramina of the skull.
Foramen Lacerum Foramen Ovale Foramen Spinosum Hypoglossal Canal Foramen Magnum Jugular Foramen Carotid Canal
Identify the main borders of the infratemporal fossa.
- Laterally: Ramus of the mandible
- Medially: Lateral pterygoid plate of sphenoid bone
- Anteriorly: Posterior aspect of maxilla
- Posteriorly: Tympanic plate, mastoid and styloid processes
- Superiorly: Infratemporal crest of sphenoid bone
- Inferiorly: Angle of the mandible
Identify the borders of the pterygopalatine fossa.
Inferior to the apex of the orbit and medial to the infratemporal fossa
- Posteriorly: pterygoid process of the sphenoid
- Anteriorly: rounded posterior aspect of the maxilla
- Medially: fragile perpendicular plate of the palatine bone forms its medial wall.
- Roof (incomplete): formed by the medial continuation of the infratemporal surface of the greater wing of the sphenoid.
- Floor: formed by the pyramidal process of the palatine bone.
Its superior larger end opens anterosuperiorly into the inferior orbital fissure. Its inferior end narrows, continuing as the greater and lesser palatine canals.
Identify the main canals and foramina connected to the pterygopalatine fossa. What is the role of these ?
There are seven openings (also known as foramina) that connect the pterygopalatine fossa with the orbit, nasal and oral cavities, middle cranial fossa and infratemporal fossa. The openings transmit blood vessels and nerves between these regions:
-Pterygomaxillary Fissure, to infratemporal fossa
-Foramen Rotundum, to middle cranial fossa
-Pharyngeal canal, to nasopharynx
-Pterygopalatine canal (=Greater Palatine Canal), to roof of oral cavity
Inferior Orbital Fissure, to orbit
-Vidian Canal (=
Pterygoid Canal), “from the middle cranial fossa and through the medial pterygoid plate (“ends just anterior to foramen lacerum”)
-Sphenopalatine Foramen, to nasal cavity
Identify the contents of the pterygopalatine fossa.
1) Terminal (pterygopalatine or third) part of the maxillary artery, and the initial parts of its branches, and accompanying veins (tributaries of the pterygoid venous plexus).
2) Maxillary nerve (CN V2), with which the pterygopalatine ganglion is associated (latter also in the fossa). Maxillary nerve branches in the fossa including infraorbital and zygomatic nerves.
3 Nerve of pterygoid canal (Vidi)
- Parasympathetic and sensory (taste) fibres of the facial nerve
- Sympathetic fibres from internal carotd plexus
Identify the main parts of the cranial base, as well as the boundaries between each.
The internal surface of the cranial base (L. basis cranii interna) has three large depressions that lie at different levels: the anterior, middle, and posterior cranial fossae, which form the bowl-shaped floor of the cranial cavity, the space enclosed within the neurocranium occupied by the brain.
The middle cranial fossa is postero-inferior to the anterior cranial fossa, separated from it by the sharp sphenoidal crests (formed mostly by the sharp posterior borders of the lesser wings of the sphenoid bones, which overhang the lateral parts of the fossae anteriorly) laterally and the limbus of the sphenoid centrally.
The boundary between the middle and the posterior cranial fossae is the superior border (crest) of the petrous part of the temporal bone laterally, and a flat plate of bone, the dorsum sellae of the sphenoid, medially
Which bones are present in the anterior cranial fossa ? Which part of the brain resides here ?
- Frontal, ethmoid and sphenoid bones
* Occupied by frontal lobes
Which of the three cranial fossas is the shallowest ?
Anterior cranial fossa
Identify important structures passing through the anterior cranial fossa. Explain the clinical significance of this.
Olfactory bulbs (CN I) receive nerve fibres from the nasal cavity via the foramina of the cribriform plate (olfaction)
Cribriform plate fractures can present with CSF rhinorrhoea
Which bones are present in the middle cranial fossa ? Which part of the brain resides here ?
- Sphenoid and temporal bones
* Occupied by temporal lobes
Identify important structures passing through the middle cranial fossa.
- The pituitary gland lies in the hypophyseal (pituitary) fossa (deepest part of sella turcica)
- The pituitary gland is surrounded by 4 clinoid processes and 2 superior projections (dorsum sellae posteriorly and tuberculum sellae anteriorly)
Which bones are present in the posterior cranial fossa ? Which part of the brain resides here ?
- Sphenoid, occipital and temporal bones
* Occupied by the cerebellum and brainstem (medulla oblongata and meninges in the foramen magnum)
What are the main functions of the mandible ?
- Site for muscle attachments (muscles of mastication)
- Foramina for passage of neurovascular structures
- Mandibular teeth within alveolar processes
Describe the main structural features of the TMJ.
- Between glenoid (mandibular) fossa of temporal bone and condylar process of mandible
- Modified hinge (atypical) synovial joint
- Articular surfaces of bone covered with fibrocartilage (not hyaline cartilage)
- Fibrocartilaginous articular disc separating the joint into superior and inferior articular cavities
- Intrinsically ‘unstable’ joint
The TMJ most often dislocated in what direction ?
Anterior dislocation most common
Describe ligamentous support of the TMJ.
- 2 extrinsic and 1 intrinsic (lateral)
- Connect mandible to cranium
1) Sphenomandibular ligament
• Primary passive support of the mandible
2) Stylomandibular ligament
3) Lateral ligament
• Strengthens TMJ laterally
• With postglenoid tubercle
prevent posterior dislocation
What are the main possible movements of the mandible ?
1) Gliding movements between temporal bone and articular disc (superior cavity)
2) Hinge and rotational movements between head of mandible and articular disc (inferior cavity)
3) Lateral movements (grinding/chewing)
What movement makes the TMJ most unstable ? Why ?
The TMJ is most unstable during depression as the condylar processes move anteriorly and lie underneath the articular eminences with the mandibular head being vulnerable to anterior dislocation into the infratemporal fossa
Identify the muscles of mastication.
Medial pterygoid (assists lateral pterygoid in protrusion + elevation)
Lateral pterygoid (protrusion)
Masseter (Elevation)
Temporalis (Elevation)
Identify the contents of the following:
Cribriform foramina in cribriform plate Optic canals Superior orbital fissure Foramen rotundum Foramen ovale Foramen spinosum Foramen lacerum Foramen magnum Jugular foramen Hypoglossal canal
- Cribriform foramina in cribriform plate: Axons of olfactory cells in olfactory epithelium that form olfactory nerves
- Optic canals: Optic nerves (CN II) and ophthalmic arteries
- Superior orbital fissure: Ophthalmic veins; ophthalmic nerve (CN V1); CN III, IV, and VI; and sympathetic fibers
- Foramen rotundum: Maxillary nerve (CN V2)
- Foramen ovale: Mandibular nerve (CN V3) and accessory meningeal artery
- Foramen spinosum: Middle meningeal artery and vein and meningeal branch of CN V3
- Foramen lacerum: Deep petrosal nerve and some meningeal arterial branches and small veins
- Foramen magnum: Medulla and meninges, vertebral arteries, CN XI, dural veins, anterior and posterior spinal arteries
- Jugular foramen: CN IX, X, and XI; superior bulb of internal jugular vein; inferior petrosal and sigmoid sinuses; and meningeal branches of ascending pharyngeal and occipital arteries
- Hypoglossal canal: Hypoglossal nerve (CN XII)
Describe the main features of a typical cervical vertebrae.
(All but C1, C2, and C7)
- Vertebral body: Small and wider from side to side than anteroposteriorly; superior surface concave with uncus of body (uncinate process); inferior surface convex
- Vertebral foramen: Large and triangular
- Transverse processes: Foramina transversarii and anterior and posterior tubercles; vertebral arteries and accompanying venous and sympathetic plexuses pass through foramina transversarii of all cervical vertebrae except C7, which transmits only small accessory vertebral veins
- Articular processes: Superior facets directed superoposteriorly; inferior facets directed infero-anteriorly; obliquely placed facets are most nearly horizontal in this region
- Spinous processes: Short (C3–C5) and bifid (C3–C6); process of C6 long, that of C7 is longer (thus C7 is called “vertebra prominens”)
Describe the main features of C1 which distinguish it from typical cervical vertebrae.
ATLAS
- Has neither a body nor a spinous process
- Paired lateral masses that serve the place of a body by bearing the weight of the cranium. These are connected by an anterior and posterior arch. Each lateral mass contains a superior articular facet (for articulation with occipital condyles), and an inferior articular facet (for articulation with C2)
- The transverse processes of the atlas arise from the lateral masses, causing them to be more laterally placed than those of the inferior vertebrae. This feature makes the atlas the widest of the cervical vertebrae, thus providing increased leverage for attached muscles
- The anterior arch contains a facet for articulation with the dens of the axis
- The posterior arch has a groove for the vertebral artery and C1 spinal nerve
Describe the main features of C2 which distinguish it from typical Cervical vertebrae.
AXIS
- Large, flat bearing surfaces AKA superior articular facets, which articulate with the inferior articular facets of the atlas to form the two lateral atlanto-axial joints.
- Dens of the axis (odontoid process), projects superiorly from its body
- Large bifid spinous process that can be felt deep in the nuchal groove, the superficial vertical groove at the back of the neck
Identify the main joints in the vertebral column.
Zygapophysial (facet) joints: plane synovial joints between the superior and inferior articular processes of adjacent vertebrae
Vertebral bodies indirectly articulate with each other via the intervertebral discs (symphyses, AKA secondary cartilaginous joint)
Describe the structure of the IV discs.
Each IV disc consists of an anulus fibrosus, an outer fibrous part, composed of concentric lamellae of fibrocartilage, and a gelatinous central mass, the nucleus pulposus.
“The intervertebral disk end plate comprises a thin layer of hyaline cartilage”
Describe the structure of facet joints.
Each joint is surrounded by a thin joint capsule.
“Hyaline cartilage covers the articular surfaces.”
What types of movements occur at each of the following:
- C0-C1
- C1-C2
- C3-C7
- C0-C1: flexion and extension + Lateral flexion
- C1-C2: flexion and extension + rotation
- C3-C7: rotation + lateral flexion
Identify the main ligaments of the vertebral column, and the function of each.
Anterior longitudinal ligament: connects the anterolateral aspects of the vertebral bodies and IV discs (prevents hyperextension)
Posterior longitudinal ligament: attached mainly to the IV discs and less so to the posterior aspects of the vertebral bodies from C2 to the sacrum (prevents hyperflexion)
Ligamentum nuchae: A sagittal ligamentous band at the back of the neck, formed of thickened supraspinous ligaments; it extends from the external occipital protuberance to the posterior border of the foramen magnum cranially, and to the seventh cervical spinous process caudally.
Ligamentum flavum: extends between lamina of adjacent vertebrae.
Cruciform ligament of the atlas: consists of the transverse ligament of the atlas plus the longitudinal band
Apical ligament: Spans between the second cervical vertebra and the skull. It lies as a fibrous cord in the triangular interval between the alar ligaments.
Ala ligament: extend from the sides of the dens of the axis to the lateral margins of the foramen magnum. Attach the cranium to the C1 vertebra and act as check ligaments in preventing excessive rotation at the joints.
Membrane Tectoria: strong superior continuation of the posterior longitudinal ligament that broadens and passes posteriorly over the median atlanto-axial joint and its ligaments. It runs superiorly from the body of C2 through the foramen magnum to attach to the central part of the floor of the cranial cavity, formed by the internal surface of the occipital bone.
Interspinous and supraspinous ligaments: join the spinous processes of adjacent vertebrae. The interspinous ligaments attach between processes, and the supraspinous ligaments attach to the tips.
Identify the main muscles and fascia of the vertebral column.
Erector spinae
Pre-vertebra muscles
Paravertebral fascia
Pre-vertebral fascia (allows gliding, extends to T3, and covers floor of the posterior triangle, cervical and brachial plexus, and third part of Subclavian artery)
Where do the vertebral artery and vein enter the vertebral column ?
• Enter Foramen Transversarium
– C7 – vein
– C6 – artery (diameter of Foramen Transversarium of C6 > C7)
What is the signifiance of the infratemporal fossa ?
Various muscles and neurovascular structures are found in this space that communicates with the temporal fossa through the interval between (deep to) the zygomatic arch and (superficial to) the cranial bones
Define Functional spinal unit.
“smallest physiological motion unit of the spine to exhibit biomechanical characteristics similar to those of the entire spine”
How may you determine adequacy of a cervical X ray ?
Ensure you can see occiput to T1 – i.e. all seven Cervical vertebra
Describe the alignment of the cervical vertebral column. How does this occur ? What is the function of this ?
Lordotic curve (43o arc)
Function: Shock absorption
• Result of: – Static factors Bone shape Disc shape – Dynamic factors Muscle Ligament
