Download Bones

Head & Neck
J.C. BYIRINGIRO
MD, MCS (ECSA)
Assistant Lecturer of Anatomy/NUR
PART I: THE SKULL
Functions of the head
• Housing and protection of brain and meninges
• Housing and protection of special sense
organs: vision, olfaction, taste hearing and
balance
• Respiration
• Mastication, deglutition (swallowing)
• Vocalization
Development of the skull
• The base of the skull develops by endochondral ossification
• The brain and cranial nerves develop before the skull, so
when the chondrocranium develops, its components form
around the nerves and form foramina.
• The chondrocranium ossifies from a number of centers.
• The last piece of cartilage to ossify is between the body of the
sphenoid bone and the occipital bone, just anterior to the
foramen magnum: this is the spheno-occipital synchondrosis.
Its epiphyseal plate exists for the growth in length of the base
of the skull and it ossifies at age 25.
• The bones of the calvarium ossify by
intramembranous ossification.
• The bones of the calvarium also ossify from separate
centers and they meet to form sutures. The process
is completed at about 3 years.
• The bones of the face are partly basal and partly
calvarial bones so they ossify both by
intramembranous and endochondral ossification.
Skull bones
• 26 bones: 22 bones + hyoid + 3 auditory
ossicles ( incus, malleus, stapes).
• 21 bones: tightly connected; mandible is
freely mobile at the temporomandibular joint.
• connective-tissue interface b/w bones =
suture.
• Except the mandible, all the other bones
constitute the cranium.
The cranium
– Neurocranium: covers
brain anteriorly, laterally
and posteriorly.
– Basicranium: supports
the brain inferiorly.
• also contributes to
interorbital region; b/w
eyes and superior to nasal
passages
– Viscerocranium/splanch
nocranium: bones of
face.
Neurocranium
Formed by:
• The frontal bone
• The parietal bone
• The occipital bone
(squamous portion)
• The Temporal bone
(squamous portion)
• Sphenoid bone (greater
wing)
The bones of the cranium and the underlying
lobes of the brain have the same name:
•The frontal bone (which houses the frontal
lobe of the brain) ossifies from 2 centers and
there are right and left frontal bones at birth.
•The metopic suture separating the 2 frontal
bones normally ossifies, leaving one large
frontal bone.
•The parietal bones are separated from each
other by the sagittal suture and from the
frontal bone by the coronal suture.
• At birth, the anterior fontanelle is
a diamond-shaped area between
the 2 frontal bones and the 2
parietal bones.
• It pulsates and bulges when the
baby cries.
• It closes by 18 months to 2 years
and is then known as the bregma.
• The parietal bones and the
occipital bone meet at the
posterior
fontanelle
which
becomes lambda, along the
lambdoid suture in the adult.
• The side wall of the skull is
completed by the
squamous part of the
temporal bone and the
greater wing of the
sphenoid bone, at the
pterion.
• This is located 4 cm above
the midpoint of the
zygomatic arch and is the
site of surgical exploration
for the middle meningeal
artery.
• The occipital bone:
– The external occipital
protuberance is located
inferior to lambda.
– The superior nuchal
lines run lateral from the
external occipital
protuberance and the
inferior nuchal lines are
situated inferiorly.
• In the cranial bones, layers of
compact tissue are the tables
of the skull;
• The outer table is thick
• The inner table is thin, dense,
and brittle, and hence is
termed the vitreous table.
• The intervening cancellous
tissue is called the diploë.
• In certain regions of the skull,
the diploë becomes
absorbed so as to leave
spaces filled with air (airsinuses) between the two
tables
•The bones are drained by diploic veins which open
into the nearest convenient venous sinus : 4 on each
side:
– frontal,
– anterior temporal,
– posterior temporal,
– occipital
•emissary foramina transmit emissary veins
connecting veins of the scalp with the dural venous
sinuses inside the skull.
– They may be seen in the parietal bone or in the
temporal bone posterior to the external
auditory meatus.
Clinical corner
• On an X-ray of the skull
there are markings which
may be mistaken for a
fracture. → These are
caused by:
(1) the middle meningeal
artery,
(2) diploic veins, or
(3) the sutures, including
the infrequent metopic
suture.
Vascular markings on XRay films.
•Less translucent - affect inner
table only
•Not sharply demarcated
•Meningeal grooves taper as
they run peripherally
•Branching pattern and
symmetrical
•Diploetic venous channels are
wide
Basicranium
Formed by:
• The basilar part of the
occipital bone
• The Petrous portion of
the Temporal bone
• The Lesser wing of the
Sphenoid bone
• The pterygoid plates of
the sphenoid bone
Viscerocranium
Formed by:
• The Maxilla
• The Palatine bone
• The Zygomatic bone
• The lacrimal bone
• The Nasal bone
• The Vomer
• The Mandible
• The inferior nasal concha
• The 3 auditory ossicles
• The hyoid bone
Sutures
The bones are separated by sutures which hold the bones
firmly together in the mature skull.
•Coronal suture: separates the frontal from parietals.
•Sagittal suture: separates two parietal bones
•Lambdoid suture: separates parietal form occipital
•Squamous suture: b/w temporal and parietal; overlapping
sutures
•Metopic suture: Present at birth, disappears when 2
frontal bones fuse.
PS: Occasionally the frontal bone may be separated into
two halves by a midline metopic suture
CRANIAL CAVITIES
5 major cavities:
•Endocranial,
•left and right orbits,
•nasal cavities,
•oral cavity,
•middle ear cavities
Endocranial cavity
• Contains brain, meninges, cerebrospinal fluid, brain’s vascular
supply and most proximal portion of cranial nerves.
• Enclosed by neurocranium and basicranium
• Basicranium:
– foramina for neurovascular bundles
– foramen magnum: spinal cord exit
• The floor of endocranial cavity divide into fossae
– anterior: frontal lobes of brain
– middle: pair temporal lobes
– posterior: cerebellum and brainstem
The interior of the base of the skull
The interior of the base of the skull comprises the anterior, middle and
posterior cranial fossae.
The anterior cranial fossa
• Bones:
• Orbital plate of the frontal bone
• Lesser wing of the sphenoid
• Cribriform plate of the ethmoid
• Foramina:
• In the cribriform plate (Olfactory
nerves)
• Optic canal (Optic nerve and
ophthalmic artery)
• Other features:
• The orbital plate of the frontal forms
the roof of the orbit.
• Lateral to the optic canals are the
anterior clinoid processes.
• The boundary between the anterior
and middle cranial fossae is the sharp
posterior edge of the lesser wing of the
sphenoid.
Clinical corner.
The cribriform plate of the ethmoid with the crista
galli transmits olfactory nerves from the upper part
of the nasal cavity; this is a possible route for
infection or escape route for CSF in skull base
fractures.
The middle cranial fossa
•
•
•
Is formed by the greater wing of the sphenoid bone and the temporal
bone.
It is occupied by the temporal lobe of the brain.
The greater wings and the body of the sphenoid bone form a butterfly
shape
.
The middle cranial fossa
•
•
The most posterior tip of the greater wing contains the foramen
spinosum.
Anterior to the foramen spinosum is the foramen ovale and then the
foramen rotundum. The foramen rotundum leads to the
pterygopalatine fossa.
The middle cranial fossa
•
•
The superior orbital fissure is a gap between the lesser wing and the greater
wing of the sphenoid leading to the orbit, just lateral to and below the optic
nerve.
The foramen lacerum is located lateroposterior to the sella.
The middle cranial fossa
The body of the sphenoid bone contains the hypophyseal fossa for the pituitary
gland. This fossa is also called the sella turcica and it is shaped like a 4-poster bed
(clinoid processes; clinical = patient is in bed).
Its maximum length is 14 mm and its depth is 8 mm. Measurements are
important because pituitary tumors cause ballooning of the sella.
Structures passing through Foramina of the middle
fossa
• Superior orbital fissure:
– Frontal, lacrimal and nasociliary branches of trigeminal nerve;
– oculomotor, trochlear and abducent nerves;
– ophthalmic veins
• Foramen rotundum:
– Maxillary branch of trigeminal nerve
• Foramen ovale:
– Mandibular branch of trigeminal nerve
• Foramen spinosum:
– Middle meningeal artery
• Foramen lacerum:
– Internal carotid artery through upper opening
FORAMINA OF THE SKULL BASE
The outside of the base of the skull
•
•
The cranial base (basicranium) is
the inferior portion of the
neurocranium (floor of the cranial
cavity) and viscerocranium minus
the mandible.
The external surface of the
cranial base.
– the alveolar arch of the maxillae;
– the palatine processes of the
maxillae;
– and the palatine, sphenoid,
vomer, temporal, and occipital
bones.
• The hard palate
– palatine processes of the
maxillae anteriorly
– horizontal plates of the palatine
bones posteriorly.
• The free posterior border of
the hard palate forms the
posterior nasal spine.
• Posterior to the central incisor
teeth is the incisive fossa, a
depression in the midline of
the bony palate into which the
incisive canals open.
• The right and left nasopalatine
nerves pass from the nose through
a variable number of incisive canals
and foramina.
• Posterolaterally are the greater and
lesser palatine foramina.
• The choanae (posterior nasal
apertures) are separated by the
vomer, a flat unpaired bone of
trapezoidal shape that forms a
major part of the bony nasal
septum.
•
The sphenoid, an irregular
unpaired bone, consists of a body
and three pairs of processes:
– greater wings,
– lesser wings, and
– pterygoid processes.
•
•
The lateral and medial pterygoid
plates, extend inferiorly on each
side of the sphenoid.
The groove for the cartilaginous
part of the pharyngotympanic
(auditory) tube lies medial to the
spine of the sphenoid, inferior to
the junction of the greater wing
of the sphenoid and the petrous
part of the temporal bone.
• Depressions in the
squamous part of the
temporal bone, called the
mandibular fossae,
accommodate the
mandibular condyles when
the mouth is closed.
• The cranial base is formed
posteriorly by the occipital
bone, which articulates with
the sphenoid anteriorly
•
•
•
•
•
•
•
•
The jugular foramen is occupied by the jugular bulb (for expansion of the
internal jugular vein) in life.
The stylomastoid foramen lies between the styloid process and the
mastoid process.
Anterior to the jugular foramen and in the petrous portion of the temporal
bone lies the carotid canal.
The foramen ovale lies at the base of the lateral pterygoid plate.
The medial pterygoid plate (with the pterygoid hamulus at its base) and
the lateral pterygoid plate are parts of the sphenoid bone.
The inferior orbital fissure leads anteriorly from the pterygoid region to
the orbit.
The hard palate is formed by the palatine process of the maxilla and by
the horizontal plate of the palatine bone. There are 3 foramina in the
horizontal plate, the larger being the greater palatine foramen.
The vomer bone in the posterior opening (the choanae) of the nasal
cavity is attached by a fibrous joint to the undersurface of the body of the
sphenoid.
The outside of the base of the skull
Anterior part of the cranial base hidden by the
bones of the face .
Many of the foramina seen on the exterior are
not visible inside the cranium.
Other features:
Bones:
•
• Temporal (Squamous, petrous and tympanic
parts and the styloid process)
• Sphenoid (body) which carries the medial
and lateral pterygoid plates
•
•
Foramina:
• Foramen magnum
• Hypoglossal canal
• Stylomastoid foramen (facial nerve)
• Jugular foramen
• Foramen lacerum (the internal carotid
through its internal opening)
• Carotid canal (internal carotid artery and
sympathetic nerves)
• Foramen spinosum
• Foramen ovale
•
•
The mastoid process is part of the petrous
temporal and contains the mastoid air
cells .
The floor of the external auditory meatus
is formed by the tympanic plate of the
temporal bone.
The carotid canal turns inside the
temporal bone to run horizontally
forwards. It then opens into the posterior
wall of the foramen lacerum before
turning upwards again to enter the cranial
cavity through the internal opening of the
foramen.
Behind the foramen spinosum is the spine
of the sphenoid which lies medial to the
mandibular fossa for articulation with the
head of the mandible.
In front of this is the articular eminence,
onto which the head of the mandible
moves when the mouth is open.
The bones of the face
The bones of the face are
suspended below the
front of the cranium and
comprise:
• the bones of the upper
jaw,
• the bones around the
orbit and nasal cavities,
• the mandible.
Bones of the Face (ct’d)
Bones:
• Maxilla
• Zygomatic
• Nasal
• Frontal
• Lacrimal
• Bones of the orbit and
nasal cavities .
• Pterygoid plates of the
sphenoid
• Palatine
The Bony orbit
• 7 bones : the maxilla,
zygomatic, frontal, ethmoid,
lacrimal, sphenoid, and
palatine bones.
• Shape of a pyramid, with its
wide base opening
anteriorly onto the face,
and its apex extending in a
posteromedial direction.
• The apex of the pyramidalshaped bony orbit is the optic
foramen, while the base (the
orbital rim) is formed:
– superiorly by the frontal
bone;
– medially by the frontal
process of the maxilla;
– inferiorly by the zygomatic
process of the maxilla and
the zygomatic bone;
– laterally by the zygomatic
bone, the frontal process
of the zygomatic bone,
and the zygomatic
process of the frontal
bone
•
•
The roof (superior wall) is made
up of the orbital part of the frontal
bone with a small contribution
from the sphenoid bone.
The medial wall consists of 4
bones: the maxilla, lacrimal,
ethmoid, and sphenoid bones.
– This part of the ethmoid bone
contains collections of ethmoid
air cells.
– Anterior and posterior
ethmoidal foramina (for the
anterior and posterior
ethmoidal nerves and vessels).
– The lacymal groove formed
and bounded by the lacrymal
bone (post. lacrymal crest) and
the frontal process of the
maxilla (ant. Lacrymal crest)
The floor (inferior wall) of the bony
orbit, which is also the roof of the
maxillary sinus:
• consists primarily of the orbital surface
of the maxilla, with small contributions
from the zygomatic and palatine bones.
•The inferior orbital fissure
The lateral wall of the bony orbit
consists of contributions from two
bones:
•anteriorly, the zygomatic bone and
•posteriorly, the greater wing of the
sphenoid bone
Nasal cavities and Paranasal sinuses
The lateral wall
• 3 conchae, which are
project medially and
inferiorly across the nasal
cavity.
• The medial, anterior and
posterior margins of the
conchae are free.
The conchae divide each nasal
cavity into four air channels:
•an inferior nasal meatus
•a middle nasal meatus
•a superior nasal meatus
•a spheno-ethmoidal recess
between the superior concha
and the nasal roof.
• The openings of the
paranasal sinuses, are on
the lateral wall and roof
of the nasal cavities.
• The lateral wall also
contains the opening of
the nasolacrimal duct,
which drains tears from
the eye into the nasal
cavity.
Nasal skeletal framework
• The unpaired bones:
–
–
–
–
ethmoid,
sphenoid,
frontal bone,
and vomer;
• The paired bones
–
–
–
–
–
nasal,
maxillary,
palatine and
lacrimal bones,
and inferior conchae
The ethmoid bone
• Contributes to the roof, lateral
wall, and medial wall of both
nasal cavities,
• Contains the ethmoidal air
cells (ethmoidal sinuses).
• Cuboidal in overall shape
• 2 ethmoidal labyrinths united
superiorly across the midline
by the cribriform plate
• Perpendicular plate which
forms part of the nasal
septum.
• Each ethmoidal labyrinth is composed of 2 sheets of bone which
sandwich between them the ethmoidal cells:
• The lateral sheet: orbital plate forming part of the medial wall of
the orbit.
• The medial sheet: 2 processes and a swelling:
– The superior and middle conchae
– The ethmoidal bulla
• The ethmoidal infundibulum
penetrates the ethmoidal
labyrinth and opens into the
frontal sinus.
• This channel is for the
frontonasal duct, which drains
the frontal sinus.
• The crista galli on the
superior surface of the
cribriform plate anchors the
falx cerebri.
• The uncinate process on
the anterior aspect of the
inferior surface of the
ethmoidal labyrinth extends
postero-inferiorly across the
maxillary hiatus in the
medial wall of the maxilla to
articulate with the inferior
concha
The medial wall
Floor of the nasal cavity (superior
view).
Paranasal Sinuses
• There are 4 paranasal
air sinuses:
–
–
–
–
Ethmoidal cells,
Sphenoidal,
Maxillary,
Frontal sinuses
• They develop as
outgrowths from the
nasal cavities and erode
into the surrounding
bones
TEMPORAL REGION
• TEMPORAL FOSSA
• INFRATEMPORAL FOSSA
TEMPORAL FOSSA
• Boundaries:
1. Sup Temporal line above
and below
2. Zygomatic arch below
3. Frontal process of the
zygomatic arch ant.
• Structures attached:
Temporalis muscle
Masseter muscle
INFRATEMPORAL FOSSA
• Below the Temporal
fossa and behind the
maxilla
• Boundaries:
– Ant: post surface of
maxilla
– Medially: Lateral
pterygoid plate
– Lat: ramus and coronoid
process of mandible
– Post: Styloid and mastoid
process
• Communicates with:
– The orbit through the
inferior orbital fissure,
– The temporal fossa
through the gap deep to
the zygomatic arch
– Pterygopalatine Fossa
through the
pterygomaxillary fissure
– Middle cranial fossa
through the foramen
ovale
INFRATEMPORAL FOSSA
• Contents:
– Medial and lateral
pterygoid muscles,
– Sphenomandibular
ligament
– Maxillary artery (1st and
2nd part and their
branches.
– Pterygoid venous plexus
and maxillary vein
– Mandibular nerve and its
branches, small part of
maxillary nerve, Chorda
tympani, otic ganglion
INFRATEMPORAL FOSSA
• Contents:
– Medial and lateral
pterygoid muscles,
– Sphenomandibular
ligament
– Maxillary artery (1st and
2nd part and their
branches.
– Pterygoid venous plexus
and maxillary vein
– Mandibular nerve and its
branches, small part of
maxillary nerve, Chorda
tympani, otic ganglion
INFRATEMPORAL FOSSA
• Contents:
– Medial and lateral
pterygoid muscles,
– Sphenomandibular
ligament
– Maxillary artery (1st and
2nd part and their
branches.
– Pterygoid venous plexus
and maxillary vein
– Mandibular nerve and its
branches, small part of
maxillary nerve, Chorda
tympani, otic ganglion
The mandible.
• The mandible consists of
the body and two rami.
• Each ramus divides into a
coronoid process and the
head, for articulation
with the mandibular
fossa.
• The mandibular foramen
transmits the inferior
alveolar nerve and
vessels.
HYOID BONE