Cranium, meninges and brain Flashcards
What is meant by a craniotomised cadaver
Top of skull has been removed, dissected in a way that the brain has been removed- see structures inside the skull without the brain.
Summarise the head
The head is composed of a series of compartments, which are formed by bone and soft tissues. They are: the cranial cavity two ears two orbits two nasal cavities, and an oral cavity
What is meant by the cranial cavity
The cranial cavity is the largest compartment and contains the brain and associated membranes (meninges)
What is meant by the orbits
The two orbits contain the eyes. They are cone-shaped chambers immediately inferior to the anterior aspect of the cranial cavity, and the apex of each cone is directed posteromedially. The walls of the orbits are bone, whereas the base of each conical chamber can be opened and closed by the eyelids.
Which regions of the head does the scalp cover
The scalp coveres the superior, posterior, and lateral regions of the head.
Summarise the bones of the skull
Skull consists of 22 bones (excluding ossicles of ear)
Cranium:
Vault
Base
Mandible Facial skeleton (viscerocranium)
What can the cranium be subdivided into
An upper domed part (the calvaria or the vault)- which covers the cranial cavity containing the brain- basically houses the brain
a base- which consist of the floor of the cranial cavity
a lower anterior part- the facial skeleton (viscerocranium)
What forms the cranium
The skull has 22 bones, excluding the ossicles of the ear. Except for the mandible, which forms the lower jaw, the bones of the skull are attached to each other by sutures, are immobile and form the cranium.
List the bones forming the cranium
Frontal Parietal x2 Occipital Temporal x2 Sphenoid- deep in centre of skull Ethmoid- top of nose
List the bones forming the viscerocranium (facial skeleton)
Maxilla x2- teeth Zygoma x2- cheek Nasal x2 Lacrimal x2 Vomer Inferior conchae x2 Palatine x2 Mandible- largest bone in skull
Explain the two parts of the cranium
Neurocranium- houses the brain- contains the base- where the brain sits- where things enter and leave- cranial vault
Viscerocranium- facial skeleton (front of skull)
Describe the bones forming the calvaria
Mainly the paired temporal and parietal bones, and parts of the unpaired frontal, sphenoid and occipital bones.
Describe the bones forming the base
Parts of sphenoid, temporal and occipital
Describe the bones forming the facial skeleton
paired nasal bones, palatine bones, lacrimal bones, zygomatic bones, maxillae and inferior nasal conchae and unpaired vomer
What is important to remember about the mandible
Not part of the cranium nor part of the facial skeleton
Why do we sniff when we cry
Lacrimal bone- inside the orbit- related to the drainage apparatus of the lacrimal glands- which are found in the top corner of the eyes- drain across to the medial side into nasal cavity.
Summarise the vomer
single bone in the middle of the skull which points upwards into the nasal cavity
Summarise the conchae
infolding bones which form the nasal cavity- increase SA and humidify the air
Summarise the palatine bones
Hard bones at the roof of the mouth
What is meant by the sutures
The many bones of the head collectively form the skull. Most of these bones are interconnected by sutures, which are immovable fibrous joints
What is special about the skull in the fetus
Bones not fully fused
In the fetus and newborn, large membranous and unossified gaps (fontanelles) between the bones of the skull, particularly between the large, flat bones that cover the top of the cranial cavity. These allow:
the head to deform during its passage through the birth canal
These fontanelles are tough- not easy to damage
postnatal growth
Two frontal bones- separated by metopic suture
See diagram!!
What happens to these fontanelles
Most of the fontanelles close during the first year of life. Full ossification of the thin connective tissue ligaments separating the bones at the suture lines begins in the late twenties, and is normally completed in the fifth decade of life
Posterior fontanelle- closes between first 2-3 months
Anterior fontanelle- closes between first 18-24 months
Describe the bones of the superior view of the skull
Forms the superior part of the calvaria
Anterior to posterior:
The unpaired frontal bone articulates with the paired parietal bones at the coronal suture
The two parietal bones articulate with each other in the midline at the saggital suture
The parietal bones articulate with the unpaired occipital bone at the lamboid suture (also known as lamba)
What are the bregma and lambda seen in the superior view
Bregma- junction of the sagittal and coronal sutures
lambda- junction of sagittal and lamboid sutures
Which foramen are seen in the superior view of the skull
The only foramina visible in this view may be the paired parietal foramina, posteriorly, one on each parietal bone, just lateral to the sagittal suture.
Emissary veins pass through this
What is special about the bones making up the calvaria
Unique in their structure, consisting of dense internal and external tables of compact bone separated by a layer of spongy bone (the diploe)
Summarise the anterior view of the skull
Includes the forehead superiorly, and, inferiorly, the orbits, nasal region, the part of the face between the orbit and upper jaw, the upper jaw and the lower jaw
Summarise the frontal bone
the forehead consist of the frontal bone- which also forms the superior rim of each orbit
just superior to the rim of the orbit are the raised supraciliary arches- more pronounced in me n- between the arches is a small depression- the glabella
medially- the frontal bone projects inferiorly to form the medial rim of each orbit
laterally, the zygomatic process of the frontal bone projects inferiorly forming the upper lateral rim of the orbit. This process articulates with the frontal process of the zygomatic bone.
Summarise the zygomatic bone
The lower lateral rim of the orbit, as well as the lateral part of the inferior rim of the orbit is formed by the zygomatic bone.
Summarise the nasal bones
Superiorly, in the nasal region the paired nasal bones articulate with each other in the midline, and with the frontal bone superiorly. The centre of the frontonasal suture formed by the articulation of the nasal bone and frontal bone is the nasion.
Laterally, each nasal bone articulates with the frontal process of each maxilla
Inferiorly, the piriform aperture is the large opening in the nasal region and the anterior opening of the nasal cavity. It is bounded superiorly by the nasal bones and laterally and inferiorly by each maxilla
Visible through the piriform aperture are the fused nasal crests, forming the lower part of the bony nasal septum, and ending anteriorly as the anterior nasal spine, and the paired inferior nasal conchae.
Summarise the maxillae
Part of the face between the orbit and upper teeth and each upper jaw is formed by the maxillae
Superiorly, each maxilla contributes to the inferior and medial ends of each orbit
Laterally, the zygomatic process of each maxilla articulates with the zygomatic bone and medially, the frontal process of each maxilla articulates with the frontal bone
Inferiorly, the part of each maxilla, lateral to the opening of the nasal cavity, is the body of the maxilla.
Inferiorly, each maxilla ends as the alveolar process, which contains teeth and forms the upper jaw.
Summarise the mandible
The lower jaw (mandible) is the most inferior part of the anterior view
Contains ramus of the manible anteriorly, and the ramus of the mandible posteriorly- these meet posteriorly at the angle of the mandible.
lower part of mandible- base
upper part- alveolar part
the alveolar part contains the teeth and is resorbed when the teeth are removed
the base of the mandible has a midline swelling (the mental protuberance) on its anterior surface where the two sides of the mandible come together. Just lateral to the mental protuberance on either side are slightly more pronounced bumps (mental tubercles)
What are the external foramina found in the anterior view of the skull
Supra-orbital foramen- supra-orbital nerve and vessel
infra-orbital foramen- infra-orbital nerve and vessel
mental foramen- mental nerve and vessel
Where does sound enter
Through the external auditory meatus- to reach the tympanic membranes
Describe the tempero-mandibular joint
clicky jaw
joint allows movement in multiple directions
open mouth wide
move jaw upwards, backwards and from side to side
Describe the lacrimal bone
Medial side of orbit
orbital plate- part that forms the orbit
Summarise the lateral view of the skull
Bones forming the lateral portion of the calvaria include the frontal, parietal, occipital, sphenoid and temporal bones.
Bones forming the visible part of the facial skeleton include the nasal, maxilla and zygomatic bones
The mandible forms the visible part of the lower jaw.
Describe the lower portions of the lateral view of the skull
The frontal bone articulates with the greater wing of the sphenoid bone, which then articulates with the parietal bone at the sphenopatietal suture, and with the anterior edge of the temporal bone at the spheno-squamous suture.
The final articulation across the lower part of the lateral portion of the calvaria is between the temporal bone and occipital bone at the occipitomastoid suture.
What is the pterion and why is it a clinically important area
The junction where the frontal, parietal, sphenoid , and temporal bones are in close proximity is the pterion. The clinical consequences of a skull fracture in this area can be very serious. The bone in this area is particularly thin and overlies the anterior division of the middle meningeal artery, resulting in an extradural haematoma
What are the parts of the temporal bone
Squamous- large flat plate- anterior and superior parts- articulates anteriorly with the greater wing of the sphenoid bone at the sphenosquamous suture, and with the parietal bone superiorly at the squamous suture
Tympanic part- below the origin of the zygomatic process- visible on the surface of this part is the external acoustic meatus (ear canal)
petromastoid part- split into petrous part and mastoid part
mastoid- most posterior- articulates with parietal bone superiorly at the parietomasotid suture and with the occipital lobe posteriorly at the occipitomastoid suture
inferiorly a large bony process (mastoid process) projects from the inferior border of the mastoid part of the temporal bone- point of attachment for several muscles.
Describe the condylar and coronoid processes seen on the lateral view of the mandible
Superior part of the ramus- chondylar and coronoid processes extend upwards
The chondylar process is involved in articulation of the mandible with the temporal lobe, and the coronoid process is the point of attachment for the temporalis muscle
Which external foramina is seen on the lateral view of the skull
Zygomaticofacial foramen- zygomaticofacial nerve- visible on the lateral surface of the zygomatic bone
Summarise the posterior view of the skull
Occipital, parietal and temporal bones are seen in the posterior view of the skull
Describe the occipital bone
Centrally, the squamous part of the occipital bone is the main structure in view. It articulates superiorly with the paired parietal bones at the lamboid suture and laterally with each temporal bone at the occipitomastoid sutures. Along the lamboid suture small islands of bone (sutural bones or wormina bones) may be observed
Describe the bony landmarks of the occipital lobe
Several bony landmarks are visible on the occipital bone. There is a midline projection (the external carotid protuberance) with curved lines extending laterally from it (superior nuchal lines). The most prominent point of the external occipital protuberance is the inion. About 1 inch below the superior nuchal lines two additional lines (the inferior nuchal lines) curve laterally
Extending downward from the external occipital protuberance is the external occipital crest
Summarise the inferior view of the skull
The base of the skull is seen in the inferior view and extends anteriorly from the middle incisor teeth posteriorly to the superior nuchal lines and laterally to the mastoid and zygomatic processes
Describe the 3 different regions of the inferior view of the skull
Anterior part- includes teeth and hard palate
Middle part- extends from behind the hard palate to the anterior margin of the foramen magnum
posterior part- extends from anterior edge of foramen magnum to the superior nuchal lines
Which two bones make up the hard palate
Maxilla- more anteriorly
Palatine- more posteriorly
Describe the fossa found in the anterior part of the inferior view of the skull
incisive fossa- anterior midline immediately posterior to the teeth (nasopalatine vessels and sphenopalatine vessels)
greater palatine foramina- near posterolateral border of hard palate on each side ( greater palatine nerve and vessels)
just posterior to the greater palatine foramina- lesser palatine foramina (lesser palatine vessels and nerve)
Describe the vomer found in the middle part of the inferior view of the skull
Anteriorly, the vomer is found in the midline, resting on the sphenoid bone. Contributes to the formation of the bony nasal septum separating the two choanae.
Summarise the sphenoid bone
Most of the anterior part of the middle part of the base consists of the sphenoid bone
Made up of a centrally placed body (which articulates anteriorly with the vomer, ethmoid, and palatine bones, posteriorly with the occipital bone and posterolaterally with the temporal bones
Paired grater and lesser wings project laterally from the body, and two downward projecting pterygoid processes immediately lateral to each choana.
Describe the mandibular fossa
Just lateral to the greater wing of the sphenoid is the squamous part of the temporal bone, which participates in the temporomandibular joint. It contains the mandibular fossa, which is a concavity where the head of the mandible articulates with the base of the skull.
Describe the occipital condyles
On each anterolateral border of the foramen magnum are the rounded occipital condyles. These paired structures articulate with the atlas (vertebra C1)- to form joint- yes joint- as can move neck forwards and backwards
No joint- joint between first and second vertebrae- rotate neck
What are the conchae covered in
mucous membranes- to humidify the air
Describe the jugular foramen
Lateral to each hypoglossal canal (which is superior to each condyle)- is a large, irregular jugular foramen formed by opposition of the jugular notch of the occipital bone and jugular notch of the temporal bone
Hypoglossal canal- hypoglossal nerve and vessels
jugular foramen- internal jugular vein, inferior petrosal sinus, glossopharyngeal nerve, vagus nerve, accessory nerve
Describe the condylar canal
Posterior to each condyle is a depression (condylar fossa) containing a condylar canal- emissary vein passes through here
Describe the foramen magnum
The occipital bone, or more specifically its basilar part, is in the midline immediately posterior to the body of the sphenoid. It extends posteriorly to the foramen magnum and is bounded laterally by the temporal bones
Continuation of the brain and spinal cord; vertebral arteries and nerve plexuses, anterior spinal artery, posterior spinal arteries, roots of accessory nerve, meninges
Describe the foramen ovale and foramen spinosum
Important features visible on the surface of the greater wing in an inferior view
on posterolateral border extending outward from the upper end of the lateral plate of the pterygoid process.
foramen ovale- mandibular nerve, lesser petrosal nerve
foramen spinosum- middle meningeal artery
Describe the stylomastoid foramen
Facial nerve
Found between styloid process and mastoid process
Describe the foramen lacerum
Filled with cartilage
Apex of temporal bone- forms one of the boundaries of the foramen lacerum- irregular opening
Describe the carotid canal
Posterolateral from the foramen lacerum along the petrous part of the temporal bone is the large circular opening for the carotid canal
internal carotid artery and nerve plexus