Week 1 - Osteology of the Skull Flashcards
What is the occipital bone?
A flat, unpaired bone that forms a major part of the posterior wall and base of the skull
It protects the cerebellum and occipital lobes of the cerebrum and provides attachment to several muscles and ligaments.
What are the three parts of the occipital bone?
- Squamous
- Condylar
- Basilar
What is the shape of the occipital bone?
Trapezoid
What is the internal surface of the squamous part of the occipital bone marked by?
Grooves produced by the dural venous sinuses
What is the cruciform eminence?
Grooves arranged like a cross on the internal surface of the squamous part
What marks the external surface of the occipital bone?
Four bony ridges known as the nuchal lines
What is the supreme nuchal line?
Extends from the midline of the occipital bone towards the lambdoid sutures on either side
What muscle attaches to the superior nuchal line?
Splenius capitis, trapezius, and occipitalis
Fill in the blank: The condylar part of the occipital bone forms the lateral walls of the _______.
Foramen magnum
What is the function of the condyloid fossa?
Articulates with the superior facet of the atlas in neck extension
What is the hypoglossal canal?
A canal through which the hypoglossal nerve exits
What does the basilar part of the occipital bone articulate with?
Temporal and sphenoid bones
What supports the medulla oblongata?
Clivus
What passes through the foramen magnum?
Medulla oblongata, accessory nerves, vertebral arteries, anterior and posterior spinal arteries, alar ligaments, tectorial membrane
List the muscles attached to the occipital bone.
- Occipitofrontalis
- Semispinalis capitis
- Obliquus capitis superior
- Trapezius
- Longus capitis
- Rectus capitis anterior
- Rectus capitis lateralis
- Rectus capitis posterior
What are the paired bones that the occipital bone articulates with?
Parietal and temporal bones
True or False: The occipital bone articulates with the atlas (C1) at the atlanto-occipital joint.
True
What is the ‘danger area of the scalp’?
Layer of loose areolar connective tissue containing valveless emissary veins
What can increased intracranial pressure cause in relation to the occipital bone?
Abducens palsy
What anatomical structure serves as a landmark for checking atlanto-occipital alignment?
Clivus
What is the frontal bone?
One of the eight bones that make up the cranium, protecting the brain
Derived from the Latin ‘frons’, meaning ‘forehead’.
What are the four parts of the frontal bone?
- Squamous part
- Orbital part (x2)
- Nasal part
The squamous part is the largest component and forms the forehead.
What features are found on the internal surface of the squamous part of the frontal bone?
- Sagittal sulcus
- Frontal crest
- Groove for the anterior meningeal artery
The sagittal sulcus contains the superior sagittal sinus.
Where are the frontal sinuses located?
Above the orbits, separated by a septum
Composed of an anterior and posterior plate.
What is the role of the supraorbital margin?
Separates the squamous part from the orbital part
Contains the supraorbital foramen where vessels and nerve pass through.
What does the orbital part of the frontal bone form?
The roof of the orbit
Comprised of a triangular-shaped flat plate extending from the supraorbital margin.
What is located in the anterolateral portion of the orbital part?
Lacrimal fossa
This is where the lacrimal gland sits.
What does the nasal part of the frontal bone articulate with?
Nasal bones and frontal processes of the maxilla
The nasal spine supports the bridge of the nose.
True or False: The frontal bone has specific muscular attachments.
False
The trochlear fossa contains a cartilaginous pulley for the superior oblique muscle.
Which bones does the frontal bone articulate with?
- Unpaired: ethmoid, sphenoid
- Paired: nasal, maxilla, lacrimal, parietal, zygomatic
A total of twelve bones.
What is frontal sinusitis?
Inflammation of the frontal sinus usually caused by infection
Can lead to complications like orbital cellulitis or meningitis if untreated.
What typically causes fractures of the frontal sinus?
Motor vehicle accidents or falls
Characteristic sign includes frontal depression in the anterior table of the skull.
What indicates a cerebrospinal fluid leak in a frontal sinus fracture?
Clear fluid leakage from the nose
This occurs due to rupture of the dura mater.
What is the skull?
A bony structure that supports the face and forms a protective cavity for the brain.
How are the bones of the skull formed?
By intramembranous ossification and joined by sutures.
What are the two main groups of skull bones?
- Cranium
- Facial bones
What is the cranium also known as?
Neurocranium
What does the cranium protect?
The brain, meninges, and cerebral vasculature.
What are the two subdivisions of the cranium?
- Cranial roof
- Cranial base
What bones comprise the cranial roof?
- Frontal
- Occipital
- Two parietal bones
What bones comprise the cranial base?
- Frontal
- Sphenoid
- Ethmoid
- Occipital
- Parietal
- Temporal
What is the clinical relevance of cranial fractures?
They can cause injury to the middle meningeal artery, leading to extradural haematoma.
What is the pterion?
An H-shaped junction between the temporal, parietal, frontal, and sphenoid bones.
What is the facial skeleton also known as?
Viscerocranium
How many bones comprise the facial skeleton?
14 bones
What are the facial bones?
- Zygomatic (2)
- Lacrimal (2)
- Nasal (2)
- Inferior nasal conchae (2)
- Palatine (2)
- Maxilla (2)
- Vomer
- Mandible
Which facial bone forms the cheekbones?
Zygomatic bones
What is the most common type of facial fracture?
Nasal fracture
What classification is used for maxillary fractures?
Le Fort classification
What is a common clinical feature of a mandibular fracture?
Pain at the fracture site and misalignment of the teeth (malocclusion)
What are sutures?
Fibrous joints unique to the skull that are immovable.
At what age do sutures typically fuse completely?
Around the age of 20.
What are the main sutures in the adult skull?
- Coronal suture
- Sagittal suture
- Lambdoid suture
What are fontanelles?
Membranous gaps between the bones in neonates due to incompletely fused sutures.
Where is the frontal fontanelle located?
At the junction of the coronal and sagittal sutures.
Where is the occipital fontanelle located?
At the junction of the sagittal and lambdoid sutures.
What does the temporal bone contribute to?
The lower lateral walls of the skull
It contains the middle and inner portions of the ear and is crossed by cranial nerves.
What joint does the lower portion of the temporal bone articulate with?
The mandible, forming the temporomandibular joint
This joint is crucial for jaw movement.
How many constituent parts make up the temporal bone?
Five parts
These parts include the squamous, tympanic, petromastoid, zygomatic, and styloid processes.
What is the largest part of the temporal bone?
The squamous part
Also known as the squama temporalis.
What muscle originates from the lower part of the squamous bone?
Temporalis muscle
This muscle is involved in mastication.
What does the zygomatic process articulate with?
The temporal process of the zygomatic bone
Together they form the zygomatic arch.
What does the tympanic part of the temporal bone surround?
The external auditory opening
It leads into the external auditory meatus.
What is the function of the styloid process?
Attachment point for muscles and ligaments
Includes the stylomandibular ligament of the TMJ.
What two parts can the petromastoid portion of the temporal bone be split into?
Mastoid and petrous parts
The mastoid process is a notable landmark.
What is the clinical significance of the mastoid air cells?
They can become infected, known as mastoiditis
They also help equalize pressure in the middle ear.
What is the primary site of attachment for the sternocleidomastoid muscle?
Mastoid process
This muscle is involved in head rotation and neck flexion.
What is the major articulation of the temporal bone?
The temporomandibular joint with the mandible
It allows for the movement of the jaw.
What can happen if middle ear infections spread to the mastoid air cells?
Mastoiditis can occur
This can potentially lead to meningitis if not treated.
What is a common cause of temporal bone fractures?
Blunt trauma to the skull
This can result in symptoms like vertigo or hearing loss.
Where is the pterion located?
Where the temporal, parietal, frontal, and sphenoid bones meet
It is the weakest point of the skull.
What can a fracture at the pterion injure?
The middle meningeal artery (MMA)
This can lead to an extradural haematoma.
What are some symptoms of increased intracranial pressure?
Nausea, vomiting, seizures, bradycardia, limb weakness
This condition may require surgical intervention.
What is the sphenoid bone?
One of the eight bones that make up the cranium, enclosing and protecting the brain.
What does the name ‘sphenoid’ mean?
‘Wedge-shaped’, derived from the Greek ‘sphenoeides’.
Describe the shape of the sphenoid bone.
‘Butterfly-shaped’.
What are the main components of the sphenoid bone?
- Body
- Greater wings
- Lesser wings
- Two pterygoid processes
Where is the body of the sphenoid bone located?
At the center of the sphenoid bone, almost completely cuboidal in shape.
What structures are contained within the body of the sphenoid bone?
Sphenoidal sinuses, separated by a septum.
Which bone does the sphenoid body articulate with anteriorly?
Ethmoid bone.
What important bony landmarks are found on the superior surface of the sphenoid body?
- Sella turcica
- Chiasmatic groove
What are the three parts of the sella turcica?
- Tuberculum sellae
- Hypophyseal fossa
- Dorsum sellae
What is the function of the anterior and posterior clinoid processes?
Attachment points for the tentorium cerebelli.
What does the greater wing of the sphenoid bone contribute to?
- Floor of the middle cranial fossa
- Lateral wall of the skull
- Posterolateral wall of the orbit
What foramina are present in the greater wing of the sphenoid bone?
- Foramen rotundum
- Foramen ovale
- Foramen spinosum
What structures pass through the foramen rotundum?
Maxillary nerve.
What structures pass through the foramen ovale?
Mandibular nerve.
What structures pass through the foramen spinosum?
Middle meningeal vessels.
What is the function of the lesser wing of the sphenoid bone?
Separates the anterior cranial fossa from the middle cranial fossa.
What forms the lateral border of the optic canal?
Lesser wing of the sphenoid.
Fill in the blank: The _______ is a slit-like gap between the lesser and greater wings of the sphenoid.
Superior orbital fissure
What does the pterygoid process consist of?
- Medial pterygoid plate
- Lateral pterygoid plate
What is the function of the medial pterygoid plate?
Supports the posterior opening of the nasal cavity.
What muscles originate from the lateral pterygoid plate?
Medial and lateral pterygoid muscles.
How many bones does the sphenoid bone articulate with?
Twelve other bones.
List the unpaired bones that articulate with the sphenoid bone.
- Occipital
- Vomer
- Ethmoid
- Frontal
List the paired bones that articulate with the sphenoid bone.
- Temporal
- Parietal
- Zygomatic
- Palatine
What is the clinical significance of the sphenoid bone?
It allows access to the pituitary gland for surgical procedures.
What type of surgery is performed through the sphenoid bone?
Endoscopic trans-sphenoidal surgery (ETSS).
True or False: The sphenoid bone is a paired bone.
False
What is the ethmoid bone?
A small unpaired bone located in the midline of the anterior cranium that encloses and protects the brain.
The term ‘ethmoid’ originates from the Greek ‘ethmos’, meaning sieve, reflecting its lightweight, spongy structure.
How many bones make up the cranium, including the ethmoid bone?
8 bones.
The ethmoid bone is one of these 8 bones.
Where is the ethmoid bone situated?
At the roof of the nasal cavity and between the two orbital cavities.
It contributes to the medial wall of the orbit and forms part of the anterior cranial fossa.
What anatomical structures does the ethmoid bone form?
- Medial wall of the orbit
- Anterior cranial fossa
- Nasal septum
- Lateral nasal wall
It separates the nasal cavity from the cranial cavity.
Which cranial nerve has a close anatomical relationship with the ethmoid bone?
Olfactory nerve (CN I).
Its fibers pass through the cribriform plate to innervate the nasal cavity.
Name the three parts of the ethmoid bone.
- Cribriform plate
- Perpendicular plate
- Ethmoidal labyrinth
Each part has specific anatomical functions and structures.
What is the function of the cribriform plate?
It forms the roof of the nasal cavity and is pierced by numerous olfactory nerve fibres.
This gives it a sieve-like structure.
What is the crista galli?
A projection from the cribriform plate that provides an attachment point for the falx cerebri.
The falx cerebri is a sheet of dura mater that separates the two cerebral hemispheres.
What does the perpendicular plate of the ethmoid bone form?
The superior two-thirds of the nasal septum.
This structure is crucial for separating the nasal passages.
What do the ethmoidal labyrinths contain?
Ethmoidal air cells (sinuses).
These large masses are located at either side of the perpendicular plate.
List the bones with which the ethmoid bone articulates.
- Nasal bones
- Maxillae
- Lacrimal bones
- Palatine bones
- Inferior conchae
- Frontal bone
- Vomer
- Sphenoid bone
The ethmoid bone articulates with a total of 13 bones.
What is a common cause of an ethmoid fracture?
Facial trauma, such as hitting the dashboard in a collision or falling from height.
These fractures can lead to various clinical symptoms.
What is anosmia?
Loss of sense of smell.
This can occur if the cribriform plate is fractured, shearing branches of the olfactory bulb.
What can happen if the ethmoidal labyrinth is fractured?
It may allow communication between the nasal cavity and the orbit, leading to orbital emphysema.
This condition allows air to enter the orbit.
What does CSF rhinorrhoea refer to?
Cerebrospinal fluid entering the nasal cavity and draining out from the nose.
This can occur due to a fracture of the cribriform plate.
How is CSF rhinorrhoea usually managed?
It often stops spontaneously and can be managed conservatively, but surgery may sometimes be required.
Spontaneous cases can also occur due to congenital or acquired defects in the ethmoid bone.
What is the nasal skeleton composed of?
Bone, cartilage, and fibro-fatty tissue
The nasal skeleton forms both the external nose and the internal nasal septum.
What are the two main parts of the nasal skeleton?
External nasal skeleton and internal nasal septum
These parts help in understanding the structure of the nose.
Which bones primarily form the external nasal skeleton?
Nasal and maxillary bones
These bones are situated superiorly in the external skeleton.
What type of cartilage primarily makes up the inferior portion of the external nose?
Hyaline cartilages
This includes lateral, major alar, minor alar, and the cartilaginous septum.
How many minor alar cartilages are usually present on each side of the nose?
3 or 4
The number of minor alar cartilages can vary.
What is the function of the internal nasal septum?
Separates the nasal cavity into two nostrils
This division is crucial for proper nasal function.
Name the paired bones that contribute to the nasal septum.
- Nasal bones
- Maxillary bones
- Palatine bones
These bones work together to form the structure of the nasal septum.
What are the unpaired bones that contribute to the nasal septum?
- Ethmoid bone
- Vomer bone
These bones are essential for the central portion of the nasal septum.
Which bone contributes to the central portion of the nasal septum?
Ethmoid bone
The ethmoid bone is one of the most complex bones in the human body.
What forms the anterior and posterior parts of the nasal septum?
- Septal cartilage (anterior)
- Vomer bone (posterior)
These components are crucial for the integrity of the septum.
What forms the floor of the nasal cavity?
Hard palate
The hard palate separates the nasal cavity from the oral cavity.
What are the two components of the hard palate?
- Palatine bone (posterior)
- Palatine process of the maxilla (anterior)
These bones together create the structure of the hard palate.
What forms the roof of the nasal cavity?
Cribriform plate of the ethmoid bone
This structure is important for the separation between the nasal cavity and the cranial cavity.
True or False: Nasal fractures are uncommon.
False
Nasal fractures are the most common facial fracture.
What typically causes nasal fractures?
Blunt trauma to the nose
This type of injury is often due to accidents or physical confrontations.
What is a common sequela of nasal fractures?
Permanent deformity
This occurs due to disruption of the bone and cartilage.
What is the mandible?
The largest and strongest bone of the face that forms the lower jaw
The mandible acts as a receptacle for the lower teeth and articulates with the temporal bone to form the temporomandibular joint.
What are the two main parts of the mandible?
The horizontal body and two vertical rami
The body is anterior, while the rami are posterior.
What are the two borders of the mandible’s body?
- Alveolar border (superior)
- Base (inferior)
The alveolar border contains sockets for the lower teeth, and the base is the attachment site for the digastric muscle.
What is the mandibular symphysis?
A small ridge of bone marking the fusion of the two halves of the mandible during development
It encloses a triangular eminence known as the mental protuberance.
Where is the mental foramen located?
Below the second premolar tooth on either side of the mandible
It acts as a passageway for neurovascular structures.
What are the bony landmarks of the mandibular rami?
- Head
- Neck
- Coronoid process
The head articulates with the temporal bone, the neck supports the head, and the coronoid process is the attachment site for the temporalis muscle.
What is the function of the mandibular foramen?
Serves as a conduit for the inferior alveolar nerve and inferior alveolar artery
It allows these structures to travel into the mandibular canal and exit at the mental foramen.
What muscles attach to the external surface of the mandibular body?
- Mentalis
- Buccinator
- Platysma
- Depressor labii inferioris
- Depressor anguli oris
These muscles are involved in facial expressions and movements.
What muscles attach to the internal surface of the mandibular body?
- Genioglossus
- Geniohyoid
- Mylohyoid
- Digastric
These muscles are involved in tongue movement and swallowing.
What muscles attach to the mandibular rami?
- Masseter
- Temporalis
- Medial pterygoid
- Lateral pterygoid
These muscles are primarily responsible for mastication.
True or False: Fractures of the mandible often occur in isolation.
False
A fracture on one side is frequently associated with a fracture on the contralateral side.
What characterizes fractures of the neck of the mandible?
Often transverse and usually accompanied by dislocation of the temporomandibular joint
These fractures are common in mandibular injuries.
What is the common characteristic of fractures of the body of the mandible?
Frequently pass through the canine tooth
This highlights the importance of evaluating the entire mandible when a fracture is present.
What are the uncommon fractures of the mandible?
- Fractures of the coronoid process
- Fractures of the neck of the mandible
Fractures of the coronoid process are usually singular.
What type of fractures occur at the angle of the mandible?
Usually oblique and may involve the alveolus of the 3rd molar
These fractures can complicate dental procedures.
What is a foramen?
An opening that allows the passage of structures from one region to another
What are the foramina of the skull collectively referred to?
Cranial foramina
What is the function of the cribriform foramina?
They allow the passage of axons of the olfactory nerve from the nasal cavity to the anterior cranial fossa
What structures pass through the optic canal?
- Optic nerve (CN II)
- Ophthalmic artery
What is the location of the superior orbital fissure?
It opens anteriorly into the orbit and enables communication between the cavernous sinus and the apex of the orbit
What structures are transmitted through the superior orbital fissure?
- Lacrimal nerve
- Frontal nerve
- Superior ophthalmic vein
- Trochlear nerve (CN IV)
- Superior division of the Oculomotor nerve (CN III)
- Nasociliary nerve
- Inferior division of the Oculomotor nerve (CN III)
- Abducens nerve (CN VI)
- A branch of the Inferior ophthalmic vein
Where is the foramen rotundum located?
At the base of the greater wing of the sphenoid, inferior to the superior orbital fissure
Which nerve passes through the foramen rotundum?
Maxillary nerve (branch of the trigeminal nerve, CN V)
What does the foramen ovale conduct?
- Mandibular nerve (branch of the trigeminal nerve, CN V)
- Accessory meningeal artery
What is the function of the internal acoustic meatus?
It connects the posterior cranial fossa and the inner ear, transporting neurovascular structures
What structures pass through the internal acoustic meatus?
- Facial nerve (CN VII)
- Vestibulocochlear nerve (CN VIII)
- Vestibular ganglion
- Labyrinthine artery
What are the three compartments of the jugular foramen?
- Anterior: inferior petrosal sinus
- Middle: glossopharyngeal nerve, vagus nerve, cranial part of the accessory nerve
- Posterior: sigmoid sinus and meningeal branches of occipital and ascending pharyngeal arteries
What nerve passes through the hypoglossal canal?
Hypoglossal nerve (CN XII)
What is the largest cranial foramen?
Foramen magnum
What structures pass through the foramen magnum?
- Medulla and meninges
- Vertebral arteries
- Anterior and posterior spinal arteries
- Dural veins
- Spinal division of the accessory nerve
What does the foramen spinosum allow to pass through?
- Middle meningeal artery
- Middle meningeal vein
- Meningeal branch of CN V3
What is unique about the foramen lacerum?
It is filled by cartilage in life, with only a few minor vessels passing through it
