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The Axial Skeleton
Eighty bones segregated into three regions
Skull
Vertebral column
Bony thorax
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Bones of the Axial Skeleton
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Figure 7.1
The Skull
The skull, the body’s most complex bony structure,
is formed by the cranium and facial bones (22 in
all)
Cranium
Made up of cranial bones
protects the brain and is the site of attachment for
head and neck muscles
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Facial bones
Facial bones
Form the framework of the face
Contain cavities for special sense organs (smell,
sight, taste, hearing)
Provide openings for the passage of air and food
Secure the teeth
Anchor the facial muscles of expression
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Facial bones
Facial bones
Form the framework of the face
Contain cavities for special sense organs (smell,
sight, taste, hearing)
Provide openings for the passage of air and food
Secure the teeth
Anchor the facial muscles of expression
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Overview of Skull Geography
The cranium can be divided into a vault and a base
The cranial vault forms the superior, lateral, and
posterior aspects of the skull (and forehead)
The cranial base (floor) forms the skull’s inferior
aspect
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Overview of Skull Geography
The internal bony ridges divide the base into 3
steps (or fossae):
Anterior cranial fossae
Middle cranial fossae
Posterior cranial fossae
The brain sits within these 3 cranial fossae
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Temporal Bones: Mastoid Region
The mastoid region contains the large mastoid
process which anchors some neck muscles
Feel it right behind your ear…go ahead, feel it!
The stylomastoid foramen allows cranial nerve VII
(the facial nerve) to leave the skull
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Temporal Bones: Petrous Region
The petrous region contributes to the cranial base
It lies between the occipital bone and the sphenoid
bone
Together w/ the sphenoid bone they form the
middle cranial fossa which supports the temporal
lobes of the brain
This region also houses the middle & internal ear
cavities
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Temporal Bones: Petrous Region
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Sphenoid Bone
Butterfly-shaped bone that spans the width of the
middle cranial fossa
The Keystone Bone: Forms the central wedge that
articulates with all other cranial bones
Consists of a central body, greater wings, lesser
wings, and pterygoid processes
Contains the sphenoid sinuses
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Sphenoid Bone
The superior surface bears the sella turcica which
bears the hypophyseal fossa that forms the
enclosure for the pituitary gland (hypophysis)
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Sphenoid Bone
The greater wings project laterally from the body and form:
Middle cranial fossa
Dorsal walls of the orbits
External wall of the skull (medial to the zygomatic arch)
The lesser wings form:
Part of the floor of the anterior cranial fossa
Part of the medial walls of the orbits
Terminate medially at the anterior clinoid process (an anchoring site
for the brain)
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Sphenoid Bone
The pterygoid processes project inferior from the body.
Function to anchor the pterygoid muscles that we use when we
chew (see arrows)
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Ethmoid Bone
Deepest of the skull bones; lies between the sphenoid and nasal
bones
Forms most of the bony area between the nasal cavity and the
orbits
The cribiform plates (seen from above) form the roof of the
nasal cavities and the floor of the anterior cranial fossa
The olfactory foramina: allow the olfactory nerves to pass
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Ethmoid Bone
Crista galli: (triangular process)
Attachment site for the dura mater (the
outermost covering of the brain)
Perpendicular plate
Projects inferiorly in the median plane
Forms the superior part of the nasal septum
(which divides the nasal cavity right and left)
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Ethmoid Bone
Right & left lateral masses:
Superior/middle nasal conchae (turbinates)
Riddled w/ ethmoid sinuses (acts as sieve)
Protrude into the nasal cavity. Circulate air w/i nasal
passages
Orbital plate:
Located on the lateral surfaces of the lateral masses
Contribute to the medial walls of the orbits
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Facial Bones
14 bones (6 paired sets) of which only the mandible and vomer are
unpaired
Most sources include:
Maxillae
Zygomatics
Nasals
Lacrimals
Palatines
inferior nasal conchae
Vomer
Mandible
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Mandible and Its Markings
The body forms the chin
The rami meet the body posteriorly at the mandibular angle
The mandibular notch separates the coronoid and condyle
processes or the rami
The coronoid process (anterior) is the insertion point for the
large temporalis muscle that elevates the lower jaw during
chewing
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Mandible and Its Markings
The mandibular condyle (posterior) articulates
with the mandibular fossa of the temporal bone
forming the temporomandibular joint
Mandibular body anchors the teeth
Alveolar margin: the superior border of the body
contains the sockets w/i which the teeth are
embedded
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Maxillary Bones (maxillae)
Medially fused bones that make up the upper jaw
and the central portion of the facial skeleton
Facial keystone bones that articulate with all other
facial bones except the mandible
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Zygomatic Bones
Irregularly shaped bones (cheekbones)
Articulate with the zygomatic processes of the
temporal bones posteriorly, the zygomatic process
of the frontal bone superiorly, and the zygomatic
process of the maxillae anteriorly
Form part of the inferolateral
margins of the orbits
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Other Facial Bones
Nasal bones
Thin medially fused bones that form the bridge of the
nose
Articulate with the frontal bone superiorly, the maxillary
bones laterally, and the perpendicular plate of the
ethmoid bone posteriorly
Cartilages form the “skeleton” of the external nose
inferiorly
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Other Facial Bones
Lacrimal bones:
Contribute to the medial walls of the orbit
Smallest and most fragile of the facial bones
Articulate with the frontal bone superiorly, ethmoid bone
posteriorly, and the maxillae anteriorly
Contains a deep groove (lacrimal fossa) that houses the lacrimal
sac that is part of the passage that allows tears to drain from the
eye to the nasal cavity
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Other Facial Bones
Palatine bones:
Fashioned from 2 bony plates
Horizontal: complete posterior portion of the hard palate
Perpendicular: forms the posterior walls of the nasal
cavity and the small parts of the orbits
3 articulating processes:
Pyramidal
Sphenoidal
orbital
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Other Facial Bones
Vomer – plow-shaped bone that forms part of the
nasal septum
Inferior nasal conchae – paired, curved bones in
the nasal cavity that form part of the lateral walls
of the nasal cavity
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Orbits
Bony cavities in which the eyes are firmly encased and
cushioned by fatty tissue
Formed by parts of seven bones:
Frontal
Sphenoid
Zygomatic
Maxilla
Palatine
Lacrimal
ethmoid
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Orbits
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Figure 7.9b
Nasal Cavity
Constructed of bone and hyaline cartilage
Roof – formed by the cribriform plate of the
ethmoid
Lateral walls – formed by the superior and middle
conchae of the ethmoid, the perpendicular plate of
the palatine, and the inferior nasal conchae
Floor – formed by palatine process of the maxillae
and palatine bone
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Nasal Cavity
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Figure 7.10b
Nasal Cavity
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Figure 7.10a
Paranasal Sinuses
Mucosa-lined, air-filled sacs found in five skull bones:
Frontal
Sphenoid
Ethmoid
Paired maxillary bones
Air enters the paranasal sinuses from the nasal cavity and
mucus drains into the nasal cavity from the sinuses
Lighten the skull and enhance the resonance of the voice
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Paranasal Sinuses
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Figure 7.11
Hyoid Bone
Lies just inferior to the mandible in the anterior neck
Only bone of the body that does not articulate directly with
another bone
Anchored by stylohyoid ligaments to the styloid processes of
the temporal bones
Acts as a movable base for the tongue
Body & horns (cornu) are points of muscle attachment that raise
and lower the larynx during swallowing and speech.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Vertebral Column
Formed from 26 irregular bones (vertebrae) connected in such a way that
a flexible curved structure results
Axial support of the trunk (skull to pelvis)
Surrounds / protects the spinal cord
Attachment point for the ribs and muscles
Fetus: 33 bones, 9 fused to form 2 composite bones: the coccyx and
sacrum
Cervical vertebrae – 7 bones of the neck
Thoracic vertebrae – 12 bones of the torso
Lumbar vertebrae – 5 bones of the lower back
Sacrum – bone inferior to the lumbar vertebrae that articulates with the
hip bones
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Vertebral Column
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Figure 7.13
Vertebral Column: Curvatures
Posteriorly concave curvatures – cervical and
lumbar
Posteriorly convex curvatures – thoracic and sacral
Abnormal spine curvatures include scoliosis
(abnormal lateral curve), kyphosis (hunchback),
and lordosis (swayback)
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Vertebral Column: Ligaments
Major supporting ligaments are: Anterior and Posterior
Continuous bands down the front and back of the spine from the cervical
vertebrae to the sacrum
Anterior longitudinal ligaments:
Posterior longitudinal ligaments
Broad, resists bending backwards attached to both the vertebrae and
the discs
Not as broad, resists bending forward, attaches only to discs
Ligamentum flavum:
Connect vertebra above and below.
Elastic consistency and strong
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Vertebral Column: Intervertebral Discs
Cushion-like pad composed of two parts
Nucleus pulposus – inner gelatinous nucleus that gives the
disc its elasticity and compressibility
Annulus fibrosus – surrounds the nucleus pulposus with a
collar composed of collagen fibers (superficially) and
fibrocartilage (internally)
Limits the expansion of the nucleus pulposus when the
spine is compressed
Binds successive vertebrae together
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Bony Thorax (Thoracic Cage)
Functions
Forms a protective cage around the heart, lungs,
and great blood vessels
Supports the shoulder girdles and upper limbs
Provides attachment for many neck, back, chest,
and shoulder muscles
Uses intercostal muscles to lift and depress the
thorax during breathing
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Sternum (Breastbone)
Anatomical landmarks: CAN PALPATE ALL OF ‘EM
jugular (suprasternal) notch:
Superior border of the maubrium
In line with T2-T3 intersection
Point where left common carotid artery splits from the aorta
sternal angle:
Hinge
Allows sternal body to move forward upon inhalation
Inline with T4-T5 intersection
Inline with 2nd pair of ribs
xiphisternal joint:
Lies opposite T9
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Gimme some of them Ribs!
There are twelve pair of ribs forming the flaring sides of the thoracic cage
All ribs attach posteriorly to the thoracic vertebrae
The superior 7 pair (true, or vertebrosternal ribs) attach directly to the
sternum via costal cartilages
Ribs 8-10 (false, or vertebrochondral ribs) attach indirectly to the sternum
via costal cartilage (or not at all)
Costal margin: inferior margin of the rib cage
Each joins the costal cartilage immediately above it
Formed by costal cartilage of ribs 7-10
Ribs 11-12 (floating, or vertebral ribs) have no anterior attachment
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Appendicular Skeleton
The appendicular skeleton is made up of the bones
of the limbs and their girdles
Pectoral girdles attach the upper limbs to the body
trunk
Pelvic girdle secures the lower limbs
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Pectoral Girdles (Shoulder Girdles)
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Figure 7.22a
Pectoral Girdles (Shoulder Girdles)
The pectoral girdles consist of:
Clavicle anteriorly & scapula posteriorly
Anteriorly, the medial end of each clavicle joins the sternum
The distal ends of the clavicle meet the scapulae laterally
The scapulae are attached to the thorax & vertebral column by muscles
The clavicle and scapula are light weight and very mobile
However, there is a price to pay…greater mobility means poor stability
often resulted in a painful dislocated shoulder
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Clavicles (Collarbones)
The acromial (lateral) end articulates with the scapula, and the sternal
(medial) end articulates with the sternum
The superior surface is smooth while the inferior surface is ridged and
grooved by ligaments
Provide attachment points for numerous muscles, and act as braces to hold
the scapulae and arms out laterally away from the body
The clavicles transmit compression force from the upper limbs to the axial
skeleton
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Scapulae (Shoulder Blades)
The posterior surface of the scapula has a prominent spine (palpate)
The spine terminates laterally at the acromion process
The acromion articulates with the acromial end of the clavicle forming the
acromioclavicular joint
The coracoid process anchors the biceps
The suprascapoid notch allows a passage way for nerves
The infraspinous, supraspinous, subscapular fossae are sites for muscle
attachment (later this semester)
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings