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Lecture name: The Axial skeleton
Written By: Shady Soghayr & Rasha Rakan
Edited By: Yousef Qandeel
The Skeletal System: The Axial Skeleton
Chapter 7
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Divisions of the Skeletal System
Types of Bones
Bone Surface Markings
Skull
Hyoid Bone
Vertebral Column
Thorax
Functions of Bone and The Skeletal
System
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Support: The skeleton serves as the structural
framework for the body by supporting soft tissues
and providing attachment points for the tendons of
most skeletal muscles.
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Protection: The skeleton protects the most
important internal organs from injury.
*Ex: The Skull protects the Brain. Vertebral Column protects spinal cord. Hip Bone protects
reproductive organs. The Rib Bones protects the lungs.
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Assistance in movement: Most skeletal muscles
attach to bones; when they contract, they pull on
bone to produce movement.
Functions of Bone and The Skeletal
System
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Mineral storage and release: Bone tissue stores
several minerals, especially Ca and PO4, which
contribute to the strength of bone.
*1.2 kg of Ca is present in our skeletal system
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Blood cell production: Within certain bones, a
connective tissue called red bone marrow produces
RBCs, WBCs, and platelets in a process called
hemopoiesis :The information of blood.
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Triglyceride storage: Yellow bone marrow
consists mainly of adipose cells, which store
triglycerides. The stored triglycerides are a potential
chemical energy reserve. *when the body needs energy we use it.
Types of Bones
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Long bones: have greater length than width and
consist of a diaphysis (shaft) and a variable
number of epiphyses or extremities. Ex.:
humerus(arm), ulna(forearm), radius(forearm), femur(leg),
tibia(leg), fibula(leg), metacarpals, metatarsals and
phalanges.
Short bones: are somewhat cube-shaped and
nearly equal in length, width, and depth. They
consist of spongy bone except at the surface,
where there is a thin layer of compact bone. Ex.:
carpal bones(wrist bones) and most of the tarsal
bones.(ankle bones)
Types of Bones
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Flat bones: are generally thin and composed of two
nearly parallel plates of compact bone enclosing a layer
of spongy bone(no projection). Ex.: cranial bones, the
sternum(in the Medline, superficial, no muscle above it /‫)عظمة القص‬, ribs
and the scapulae.
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Irregular bones: have complex shapes and cannot
be grouped into any of the three categories just
described. They also vary in the amounts of spongy and
compact bone they contain. Ex.: the vertebrae, certain
facial bones, and the calcaneus.
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*all the bones tarsal bones are classified as short bones except for the
calcaneus that is classified as irregular
Types of Bones
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Sesamoid bones: develop in certain tendons where
there is considerable friction, compression, and physical
stress. They are not always completely ossified and
measure only a few millimeters to centimeters in
diameter(like our thumbs) except for the two patellae
(kneecaps), the largest of the sesamoid bones.
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Sutural bones: Small bones located in sutures of
cranial bones
*joints of the skull, connection between the skull bones, they are the only
type of joints that are immovable because the skull bones don’t move.(that’s
why they look like a single bone).
*most of it is located in the suture between the parietal and occipital bones.
*they are classified on their own because not all people have them >
Types of Bones
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Bones can be classified into five types based on
shape:
Long
Short
Flat
Irregular
Sesamoid
*the formation
of blood cells
happens in the
long bones
Divisions of the Skeletal System
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The human skeleton consists of 206 named bones
Bones of the skeleton are grouped into two principal
divisions:
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Axial skeleton
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Consists of the bones that lie around the longitudinal axis of
the human body
Skull bones, auditory ossicles (ear bones), hyoid bone(the
only bone that is not articulate with other bones), ribs, sternum
(breastbone), and bones of the vertebral column
Appendicular skeleton
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Consists of the bones of the upper and lower limbs
(extremities), plus the bones forming the girdles (shoulder
girdles, pelvic girdles –connects lower limb with the hip bone) that
connect the limbs to the axial skeleton (the function of girdles)
Divisions of the Skeletal System
Divisions of the Skeletal System
Upper and lower
limbs are the last
ones to develop
and their
developing looks
like budding
Bone Surface Markings
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Bones have characteristic surface markings
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Structural features adapted for specific functions
There are two major types of surface markings:
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1) Depressions and openings
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Allow the passage of blood vessels and nerves or form
joints
2) Processes
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Projections or outgrowths that form joints or serve as
attachment points for ligaments and tendons
Bone Surface Markings
Notes
*Fossa : Contains Something
Ex: *anterior cranial fossa contains the anterior part of the brain
*iliac fossa (in the hip bones) contains iliacus muscle
*Sulcus : ‫مجوف وليس مفتوح‬
*Meatus : canal / ‫ مغطاة من األعلى بعظم ومن فوق بعظم‬/ contains something
Ex: *anterior auditory meatus contains vestibulocochlear nerve
*Facet : is located in areas of articulation between movable bones, when
there’s bone to bone contact in the areas of movement, there will be high
friction, so the area between them was covered to decrease the friction
*spinous process : very sharp, like the needle
*Trochanter : large projection, there are 2 trochanters located in the beginning
of the largest bone (femur), they are only located in it - the bone is large so the
projections are large as well*Tubercle : they are the projections of the humerus bones in the arm, they are
smaller than trochanters due to the nature of their bones (humerus smaller than
femurs)
Copyright 2009, John Wiley & Sons, Inc.
Skull
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auditory ossicles
(ear bones) are
not classified as
one of the skull
bones
Skull (cranium)
Consists of 22 bones
Bones of the skull are grouped into two
categories:
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Cranial bones (most of them singular)
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Eight cranial bones form the cranial cavity
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Frontal bone, two parietal bones, two temporal bones, the
occipital bone, the sphenoid bone, ethmoid bone
Facial bones (most of them paired)
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Fourteen facial bones form the face
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Two nasal bones, two maxillae, two zygomatic bones, the
mandible, two lacrimal bones, two palatine bones, two inferior
nasal conchae, vomer
Skull
Skull
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The cranial and facial bones protect and support
special sense organs and the brain
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Besides forming the large cranial cavity, the skull
also forms several smaller cavities
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Nasal cavity
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Orbits (eye sockets)
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Paranasal sinuses
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Small cavities which house organs involved in hearing
and equilibrium
Skull
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Immovable joints (in adults) called sutures fuse
most of the skull bones together
The skull provides large areas of attachment for
muscles that move various parts of the head
Skull and facial bones provide attachment for
muscles that produce facial expressions
The facial bones form the framework of the face
and provide support for the entrances to the
digestive (Oral cavity) and respiratory (Nasal
cavity) systems
Skull (Cranial Bones)
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Frontal Bone
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Parietal Bones
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Form the sides and roof of the cranial cavity
Temporal Bones
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Forms the forehead
*the most anterior bone of the skull and slot in the superior part where
attached with two parietal bones in an immovable join(coronal suture)
And becomes slightly vertical above supraorbital margin.
After it becomes vertical slightly goes horizontal making the roof of the
orbital cavity and contains the frontal (lob)of the brain.
Supraorbital foramen passage supraorbital nerve
Form the lateral aspects and floor of the cranium
Occipital Bone
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Forms the posterior part and most of the base of the cranium
Skull (Cranial Bones)
continue
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Sphenoid Bone
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Lies at the middle part of the base of the skull
Ethmoid Bone
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Located on the midline in the anterior part of the cranial floor medial to
the orbits
A major superior supporting structure of the nasal cavity
Contain thin projections called conchae which are lined by mucous
membranes
Increased surface area in the nasal cavity helps to humidify inhaled air
trapping inhaled particles
Copyright 2009, John Wiley & Sons, Inc.
‫‪Frontal Bone‬‬
‫الفورامين تكون مغلقه بالعظم من جميع الجهات اما النوتش فال تكون مغطاة بالعظم من االسفل و االنسان لديه اما‬
‫نوتش او فورامين و كالهما يحتوي على اعصاب‬
‫‪Flat surface= sequama‬‬
Parietal Bones
majorly make the superior part of the clavera (the superior part
of the skull)
Copyright 2009, John Wiley & Sons, Inc.
continue
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each parietal bone articulate with 5 other bones (frontal , 2nd
parietal , sphenoid , occipital , temporal)
1-Between the two parietal there is the sagittal suture
2-lamdoid suture separate the two parietals from the sterile
occipital bone
3-temporal bone that articulate with sphenoid bone , parietal
bone and occipital bone
The shape of the articulations(articular surface) majorly is
denticulate (tooth-like) but with the temporal bone is beveled
Copyright 2009, John Wiley & Sons, Inc.
Temporal Bones
Smooth surface
Rough surface
Large
projection
which connects
to the muscles
Continue to temporal bone
*temporal bones are smooth flat surface
 Housing the very important structure(hearing organ +
equilibrium organ)
 External auditory meatus in the tympanic passes the sound to
the middle ear
 Projection: generally is an attachment to muscle
 Zygomatic arch :consists of two processes; zygomatic process of
the temporal bone and temporal process of zygomatic bone
 Zygomatic process of the temporal bone is articulate with
temporal process of the zygomatic bone
The internal auditory meatus passage for two important cranial
nerves(stipulu popular responsible of equilibrium)
and the(facial)that is responsible about face expressions
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Copyright 2009, John Wiley & Sons, Inc.
Sphenoid Bone
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Can we see the
sphenoid bone
externally?
Yes
Continue for the sphenoid bone
Articulate with the frontal bone and a majorly with the
temporal bone and with the parietal bone
 We can see a small portion of the greater wing externally
 The greater wings and lesser wings articulate with the
frontal and ethmoid bone and make part of the cranial
fossa(majorly made of frontal bone and part of it is made
of lesser wing) which carry the frontal lob of the brain
 Articulate with all other cranial bones :
frontal , parietal , temporal , ethmoid , occipital
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Copyright 2009, John Wiley & Sons, Inc.
Sphenoid Bone