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Skeletal System
Introduction
• The framework of bones and cartilage that
protects our organs and allows us to move is
called the skeletal system.
• The branch of medicine that deals with the
preservation and restoration of the skeletal
system, articulations (joints), and associated
structures is called orthopaedics.
The skeletal system performs the
following functions:
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Support
Protection (for internal organs)
Movement
Mineral storage
Storage of blood cell-producing cells
Storage of energy
Bone Composition
• Bone is very strong for
its relatively light weight
• The major components
of bone are:
– Calcium carbonate
– Calcium phosphate
– Collagen
– Water
Cortical Bone
Spongy Bone
Medullary (marrow) cavity
Bone Composition Cont’d
• Calcium carbonate and calcium phosphate:
– Make up 60-70% of bone weight
– Provide much of the bone’s stiffness and resistance to pressing or
squeezing forces
• Collagen (a protein):
– Gives bone its characteristic flexibility and contributes to its ability
to resist pulling and stretching forces
– With aging, collagen is lost progressively and bone becomes more
brittle.
• Water
– Bone consists of much smaller proportion of water than other
body parts
Bone Classification
• According to the degree of porosity, bone can
be classified into two general categories:
– Cortical bone (low porosity)
– Spongy or cancellous bone (high porosity)
Cancellous bone
Compact Bone
•Porosity
•High (Low mineral
content and high
collagen)
•Low (High mineral
content and low
collagen)
•Structure
•Honey comb
•
•Characteristic
•Provides more flexibility
but is not as stress
resistant
•Stiffer and can resist
greater stress but less
flexible
•Function
•Shock absorption due
to its better ability to
change shape are
important
•Withstanding stress in
body areas that are
subject to higher impact
loads
•Location
•e.g. vertebrae
•Long bones (e.g. bones
of the arms and legs)
Compact
Effect of Fitness on Bone
• When bones are subjected to regular physical activity
and habitual loads, they tend to become denser and
more mineralized
– e.g. Right forearm of the right-handed tennis player is
more dense than her left one from using it more
frequently
• Inactivity works in the opposite direction, leading to
a decrease in weight and strength.
– e.g. Loss of bone mass has been noted in bed-ridden
patients, inactive senior citizens, and astronauts
Types of Bones
• There are five principal types of bones
• All bones are classified based on shape
1. Long bones
(e.g. thighs, legs, toes, arms, forearms,
and fingers)
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greater length than width
consist of a shaft and extremities (ends)
slightly curved for strength
consist mostly of compact bone (dense bone
with few spaces) but also contain considerable
amounts of spongy bone (bone with large
spaces)
2. Short bones
(e.g. wrist, ankle bones)
• Somewhat cube-shaped and nearly equal in
length and width
• Spongy except at the surface where there is a
thin layer of compact bone
3. Flat bones
(e.g. cranial bones, sternum, ribs,
scapulas)
• Generally thin and composed of two more or
less parallel plates of compact bone enclosing
a layer of spongy bone
• Flat bones afford considerable protection and
provide extensive areas for muscle
attachment
4. Irregular bones
(e.g. vertebrae, and certain facial
bones)
• Have complex shapes and cannot be grouped
into any of the other three categories
• They vary in the amount of spongy and
compact bone
5. Sesamoid bones
• Are small bones in tendons where
considerable pressure develops, for instance,
the wrist
• Their number varies greatly from person to
person
• All people have at least two sesamoid bones:
the patella (kneecap)
Divisions of the Skeletal System
• The adult human skeleton consists of 206 bones
grouped as the axial skeleton and the appendicular
skeleton.
• The axial division consists of the bones of the skull,
auditory ossicles, hyoid bone, ribs, breastbone, and
the backbone.
• The appendicular division consists of the bones of
the upper and lower extremities (limbs), plus the
bones called girdles, which connect the extremities
to the axial skeleton.
• There are 80 bones in the axial division and 126 in
the appendicular. Listed below are the divisions of
the skeletal system.
Axial Skeleton
Skull
Sternum
Ribs
Vertebral
Column
Skull
• Divided into two parts:
a) Calvaria
b) Face
a) Calvaria
Frontal Bone
Parietal Bone
Occipital Bone
Temporal Bone
Calvaria Cont.
• May be fractured in blows to the
skull (e.g., in hockey, being
checked and hitting the skull on
the ice)
• Temporal bone:
– more fragile of the calvaria bones
– overlies one of the major blood
vessels
– if fractured and displaced internally
= medical emergency (picture)
b) Facial Bones
Lacrimal Bone
Nasal Bone
Zygomatic Bone
Maxilla Bone
Mandible Bone
Vertebral Column
7 Cervical Vertebrae (of the neck)
Lumbar vertebra,
lateral view
12 Thoracic Vertebrae (of the chest)
Lumbar vertebra,
superior view
5 Lumbar Vertebrae (of the lower back)
Sacrum (mid-line region of buttocks)
Coccyx (4 or 5 fused vertebrae of the tail bone)
Vertebral Column
• Vertebrae are arranged in a cylindrical column
interspersed with fibrocartilaginous
(intervertebral) discs
• Function:
– provides a strong and flexible support for the body
and the ability to keep the body erect
– the point of attachment for the muscles of the back.
– protect the spinal cord and nerves
– absorbs shock through the intervertebral discs without
causing damage to other vertebrae
Ribs
• Twelve pairs
• Made up of :
– bone
– cartilage which strengthen the chest cage and
permit it to expand.

Curved and slightly twisted making it
ideal to protect the chest area
Ribs Cont’d
• All 12 pairs of ribs articulate with the twelve thoracic vertebrae
posteriorly
• Classified into three groups based on anterior attachment:
(picture)
– true ribs
• 1-7
• attach to both the vertebrae and the sternum
– false ribs
• 8-10
• attach only to the sternum indirectly, through 7th rib
– floating ribs
• 11 and 12
• only attach to the vertebral column
The Ribs
Manubrium
Sternal Body
True Ribs
(1-7)
Xiphoid Process
False Ribs
(8-10)
Costal Cartilages
Floating Ribs
(11-12)
Sternum
• Mid-line breast bone
• The clavicles and ribs one to seven
articulate with the sternum
Sternum – comprised of
the manubrium, sternal
body and xiphoid process
Appendicular skeleton
Consists of:
 1. The pectoral gridle (chest)
 2. Pelvic girdle (hip)
 3. The upper limbs
 4. The lower limbs
1.Pectoral Girdle
Consists of:
Clavicle
Scapula
– Scapula (shoulder blade)
– Clavicle (collar bone)

Allows the upper limb great mobility
 The sternoclavicular joint is the only point of
attachment between the axial skeleton and the
pectoral girdle
2. Pelvic Girdle
• Formed by pair of os coxae (hip
bones)
• supports the bladder and
abdominal contents
• Attachment:
– Posteriorly – join with the sacrum
– Anteriorly - join to each other
anteriorly
– Laterally – join to the head of thigh
bone through a cup-shaped
acetabulum
3. Upper Limb
• Humerus
– The arm bone
– shoulder to elbow
Humerus
• Radius and Ulna
– The forearm bones
– elbow to wrist
– the radius being located on the
thumb side of the hand
– when you pronate the forearm,
the radius is actually crossing
over the ulna - try it yourself
Radius
Ulna
Upper Limb Cont.
Carpals
Proximal
Phalanx
Metacarpals
Phalanges
Distal
Phalanx
Middle
Phalanx
4. Lower Limb
• Femur
– thigh bone
– from hip to knee
Femur
• Patella
– knee cap
– sesamoid bone in the
tendon of the
quadriceps muscles
(thigh)
Patella
Lower Limb Cont’d
• Tibia and Fibula
– leg bones
– From knee to ankle
– Tibia is medial and fibula is
lateral
Fibula
• Medial malleolus and Lateral
malleolus
– The distal ends of the tibia and
fibula, respectively
– commonly referred to as the
"ankle bones"
– can be easily palpated
Tibia
Lat. malleolus
Med. malleolus
Lower Limb Cont’d
• Tarsals
– ankle bones
– calcaneus or the heel bone
– talus
• Metatarsals
– 5 bones of the foot
– unite with the toes
• Phalanges
– toe bones
– three per toe except the big
toe - proximal, middle and
distal
Talus
Calcaneus
Tarsals
Metatarsals
Phalanges
Skeletal Surface Markings
• The surfaces of bones have various structural
features adapted to specific functions. These
features are called surface markings. Long
bones that bear a great deal of weight have
large, rounded ends that can form sturdy
joints, for example. Other bones have
depressions that receive the rounded ends.
Depressions and Openings
Foramen
an opening through which blood
vessels, nerves, or ligaments
pass
Example:
Meatus
a tubelike passageway running
within a bone
Example:
Paranasal
sinus
an air-filled cavity within a bone
connected to the nasal cavity
Fossa
a depression in or on a bone
Example:
Processes that form Joints
Condyle
a large, rounded articular
prominence
Example:
Head
a rounded articular projection
supported on the constricted
portion (neck) of a bone
Example:
Facet
a smooth, flat surface
Example:
Processes to which tendons, ligaments and other connective tissues
attach
Tuberosity
a large, rounded, usually
roughened process
Example:
Spinous
a sharp, slender projection
process
Example:
Trochanter a large, blunt projection
found only on the femur
Example:
Crest
Example:
a prominent border or ridge