The human skeleton is the internal framework of the body. It is composed of around 270 bones at birth – this total decreases to around 206 bones by adulthood after some bones have fused together. The bone mass in the skeleton reaches maximum density around age 21. The human skeleton can be divided into the axial skeleton and the appendicular skeleton. The axial skeleton is formed by the vertebral column, the rib cage, the skull and other associated bones. The appendicular skeleton, which is attached to the axial skeleton, is formed by the shoulder girdle, the pelvic girdle, and the bones of the upper and lower limbs. he skeleton serves six major functions: support, movement, protection, production of blood cells, storage of minerals and endocrine regulation. The skeleton provides the framework which supports the body and maintains its shape. The pelvis, associated ligaments and muscles provide a floor for the pelvic structures. Without the rib cages, costal cartilages, and intercostal muscles, the lungs would collapse.

1. SKELETAL SYSTEM
ANATOMY & PHYSIOLOGY
UNIT-IV
Edited by Aiman Ali

2. OBJECTIVES
At the end of this session the students will be able to:
• Define skeletal system
• List the functions of the skeletal system
• Discuss the structure, types and functions of bone
• Identify the bones of axial & appendicular skeleton
• Describe the various markings on the surface of bones
• Identify Cranial sutures and fontanels
• Describe the bones of:
• Skull
• Vertebral column
• Rib cage

4. • Support- framework that supports body and
cradles its soft organs.
• Protection- for delicate organs, heart, lungs,
brain.
• Movement- bones act as levers for muscles.
• Blood cell formation- hemopoiesis
• Mineral storage- calcium & phosphate
• Acid-base balance: Buffering capacity by
absorbing and releasing alkaline salts.

5. • Long Bones- humerus, radius, ulna, femur,
tibia, fibula, metacarpals, metatarsals,
phalanges,
• Short Bones- usually cuboidal, e.g. carpals
(except pisiform), tarsals (except calcaneus)
• Flat Bones- cranial, scapula, ribs, sternum.
• Irregular Bones- vertebrae, hip bones,
some facial bones, calcaneus.
• Sesamoid- patella, pisiform, etc.

6. STRUCTURE OF BONE
A typical long bone consists of:
1. Diaphysis (=growing b/w) is the bone’s shaft or body which is the
main long portion of bone.
2. Epiphyses (=growing over; singular is epiphysis) are the proximal and
distal ends of bone.
3. Metaphyses (meta=b/w; singular is metaphysis) are the regions b/w
diaphysis and epiphysis. In a growing bone, each metaphysis includes
an epiphyseal plate which is a layer of hyaline cartilage that allows the
diaphysis to grow in length. When a bone stops its growth in length
about the age of 21, the cartilage in the epiphyseal plate is replaced by
bone which is then called epiphyseal line.

7. METAPHYSIS

9. STRUCTURE OF BONE CONT…
4. Articular Cartilage is a thin layer of hyaline cartilage
covering the epiphyseal ends to form articulation (joint)
with another bone.
5. Periosteum is a fibrous dense irregular connective
tissue which covers the bone surfaces between the
articular cartilages.
• Periosteum helps in protection, fracture repair, and
attachment of ligaments and tendons.
6. Medullary Cavity/marrow cavity is a hollow cylindrical
space within the diaphysis which contains fatty yellow
bone marrow in adults.
7. Endosteum is a connective tissue thin layer that lines
the medullary cavity.

10. BONE SURFACE MARKINGS
• Bones have functional surface markings.
• Two major types of surface markings are:
1. Depressions and Openings—to form joints or allow the passage of blood
vessels and nerves.
2. Processes (projections or outgrowths) either help form joints or serve as
attachment points for connective tissue like ligaments and tendons.

11. BONE SURFACE
MARKINGS/FEATURES
Marking Description Example
Fissure Narrow slit Superior orbital fissure
Foramen (=hole) Opening Foramen magnum
Fossa Shallow depression Lacrimal fossa
Sulcus (=groove) Furrow along a bone
surface
Intertubercular sulcus of
humerus
Meatus (=passageway) Tube-like opening External auditory meatus
Processes forming joints
Condyle (knuckle) Large round protuberance Lateral condyle of the
femur
Facet Smooth flat articular
surface
Articular facets of
vertebrae
Head Prominent end of bone Head of Femur

12. •
Process forming
attachments
Crest Prominent ridge Illiac Crest
Epicondyle Projection above a
condyle
Medial epicondyle of
femur
Trochanter Large projection Femur trochanter
Tubercle (=knob) Small rounded
projection
Greater tubercle of
humerus
Tuberosity Large rounded
projection
Tibial Tuberosity

13. HISTOLOGY OF BONE TISSUE
• Bone or osseous tissue contains an abundant extracellular matrix which
consists of about 25% water, 25% collagen fibers, and 50% crystalized
mineral salts.
• The most abundant mineral salt is calcium phosphate [Ca3(PO4)2]. It
combines with another mineral salt, calcium hydroxide, to form crystals of
hydroxyapatite [Ca10(PO4)6(OH)2]. As the crystals form, they combine with
still other mineral salts like calcium carbonate, and ions of Mg, K,
fluoride, and sulphate. This process of mineralization with collagen fibers
is known as calcification.

14. HISTOLOGY OF BONE TISSUE CONT….
Four types of cells are present in bone tissue as:
1. Osteogenic Cells, from which almost all other connective tissues are
formed.
• They are the only bone cells that undergo division.
• They differentiate into osteoblasts.
2. Osteoblasts (blasts=buds) are bone-building cells. They synthesize and
secrete collagen fibers needed to build extracellular matrix of bone tissue.
Osteoblasts are surrounded by and become trapped into the matrix, and
result in osteocytes.

15. HISTOLOGY OF BONE TISSUE CONT….
3. Osteocytes are main cells in bone tissue that maintain its daily
metabolism. The do not undergo cell division.
4. Osteoclasts (clast = break) are huge cells derived from the fusion of as
many as fifty monocytes. These cells release powerful lysosomal enzymes
and acids that digest proteins and mineral components of the underlying
bone matrix. This breakdown of bone matrix is known as resorption.
• Resorption is part of the normal development, maintenance, and repair
of bone.

16. COMPACT BONES
• Compact bones are relatively stronger than spongy bones.
• Blood vessels, lymphatic vessels, and nerves penetrate
compact bone through transverse perforating or Volkmann’s
canal.
• A longitudinal canals run through the bone called central or
haversian canals.
• Around the haversian canals are concentric lamellae—rings
of calcified extracellular matrix like the rings in trunk of a
tree.
• Between the lamellae are small spaces called lacunae.
• Lacunae contain osteocytes.
• Radiating in all directions from the lacunae are tiny
canaliculi. All these components form haversian system.

17. SPONGY BONES
• Spongy bones are lighter and do not contain haversian systems or
osteons.
• They consist of irregular columns called trabeculae (=little beams).
• Most of the bone tissue of short, flat, and irregular bones, and
epiphysis of long bones are spongy bones.

18. Distal
epiphysis
Proximal
epiphysis
diaphysis
yellow marrow
epiphyseal line
periosteum
compact bone
spongy bone
Endosteum
hyaline cartilage
Sharpey’s fibers

19. DIVISION OF SKELETAL SYSTEM
• Skeletal system of adult consists of 206 bones and is divided into Axial
and Appendicular skeleton.
• Axial skeleton consists of 80 bones while Appendicular skeleton has 126
bones.

22. Axial Skeleton (80)
 Skull (22)
- Cranium (8)
- Face (14)
 Hyoid (1)
 Auditory Ossicles (6)
- Malleus (2)
- Incus (2)
- Stapes (2)
 Vertebral Column (26)
 Thorax
- Sternum (1)
- Ribs (24)
Appendicular Skeleton (126)
 Pectoral girdles (4)
• Clavicle (2)
• Scapula (2)
 Upper Limbs
• Humerus (2)
• Ulna (2)
• Radius (2)
• Carpals (16)
• Metacarpals (10)
• Phalanges (28)
 Pelvic(hip) girdles
• Hip, pelvic or OS Coxae
(2)
 Lower Limbs
• Femur (2)
• Patella (2)
• Tibia (2)
Fibula (2)
Tarsals (14)
Metatarsals
(10)

23. AXIAL SKELETON
Cranial Bones (8)
• Frontal bone (1)
• Temporal bones (2)
• Parietal bones (2)
• Occipital bone (1)
• Sphenoid Bone (1)
• Ethmoid bone (1)
Facial bones (14)
• Nasal bones (2)
• Inferior nasal conchae
(2)
• Vomer (1)
• Lacrimal bones (2)
• Zygomatic bones (2)
• Maxillae (2)
• Mandible (1)
• Palatine bones (2)

26. CRANIAL BONES
1. Frontal Bone: Forms forehead, roofs of the orbits, and most of the
anterior part of the cranial floor.
• Soon after birth, the left and right sides of the frontal bone are united by
the metopic suture, which usually disappears around the age of 8 years.
Foramen:
• Supraorbital—allows supraorbital nerve and artery.
Sinuses:
• Frontal sinuses (one of the paired paranasal sinuses) opening into the
nasal cavity.

27. CRANIAL BONES CONT…
2. Parietal Bones (pariet= wall):
• The two parietal bones form the greater portion of the sides and roof of
the cranial cavity.
• The internal surfaces of the parietal bones contain many protrusions and
depressions that accommodate the blood vessels supplying the dura
mater.

28. CRANIAL BONES CONT…
3. Temporal Bones:
• They form the inferior lateral aspects of the cranium and
part of the cranial floor.
• The projection from its inferior anterior part is zygomatic
process, which articulates with the temporal process of the
zygomatic bone.
• These two processes form the zygomatic arch superiorly.
• A socket called the mandibular fossa is located on the
inferior posterior surface of the zygomatic process of each
temporal bone.
• Anterior to the mandibular fossa is an elevation called
articular tubercle. These two articulate with the mandible
to form temporomandibular joint

29. TEMPORAL BONE CONT…
• Posterior and inferior to the ear canal is the mastoid portion of the
temporal bone which directs sound waves to the ear.
• Posterior and inferior to the external ear canal is mastoid process to
which several neck muscles are attached.
• The styloid process (styl=stake or pole) projects inferiorly from the
inferior surface of the temporal bone which serves as a point of
attachment for muscles of tongue, pharynx, and hyoid bone.

30. TEMPORAL BONE CONT…
Foramina in the temporal bones:
• Stylomastoid foramen, between the styloid and the mastoid process,
permits facial nerve (VII) and stylomastoid artery.
• Carotid foramen, in the petrous portion (=rock), allows carotid artery
to pass.
• Jugular foramen, posterior to the carotid foramen, permits jugular
vein.

31. CRANIAL BONES CONT…
4. Occipital Bone (occipit = back of head):
• Forms the posterior and most of the base of the cranium
• The foramen magnum (= large hole) is in the inferior part of the bone.
• The medulla oblongata connects with spinal cord via this foramen.
• Vertebral and spinal arteries also pass through it.
• The occipital condyles articulate with the atlas to form the atlanto-
occipital joint.

32. CRANIAL BONES CONT…
5. Sphenoid Bone (=wedge-shaped):
• A butterfly shaped bone lying at the middle part of the base of the skull.
• It is the keystone as it articulates with the rest of all the cranial bones
and hold them.
• The sella turcica (sella=saddle; turcica= turkish) on which there is a
depression called hypophyseal fossa that contains pituitary gland.
• It forms a part of the nasal floor, side walls, and rear wall of the orbit.
• The sphenoidal sinus opens into the nasal cavity.
• The optic foramen allows optic nerve (II) and opthalmic artery to pass
into the orbit:

33. CRANIAL BONES CONT…
6. Ethmoid Bone (like a sieve): Major superior supporting
structure of nasal cavity.
• Is sponge like, located on the midline in the anterior part of
the cranial floor medial to the orbits.
• It is anterior to sphenoid and posterior to the nasal bones.
It forms:
i. The anterior part of the cranial floor.
ii. The medial wall of the orbits.
iii. The superior portion of the nasal septum
iv. Most of the superior side walls of the nasal cavity.

34. ETHMOID BONE CONT…
• The cribriform plate (cribri=sieve ) forming the roof of the nasal cavity
contains olfactory foramina which permit olfactory nerves to pass.
• Projecting superiorly from the cribriform plate is a triangular process
called crista galli (crista= crest; galli= cock), which serves as a point of
attachment for the membranes that separate the two sides of the brain.
• The two projections of ethmoid lateral to the nasal septum are superior
and middle nasal conchae or turbinates which swirl the inhaled air.

35. FONTANELS
• Fontanels (=little fountains) At birth the mesenchyme-filled spaces in the
cranial bones are called fontanels.
Four fontanels at the time of birth are:
1. Anterior Fontanel—the largest one that closes 18 to 24 months.
2. Posterior Fontanel—closes about 2 months.
3. Anterolateral Fontanels— paired, that close about
3 months after birth.
4. Posterolateral Fontanels—Paired, which close
about 12 months.

36. CRANIAL SUTURES
• Sutures (=seam) are immovable joints in adult that holds most of the
skull bones together.
Four prominent sutures in the cranium are:
1. Coronal Suture (=crown) unites frontal and both parietal bones.
2. Sagittal suture (=arrow), unites the two parietal bones.
3. Lambdoidal Suture, unites parietal bones and occipital bone.
4. Squamous Sutures (squam = flat), unite parietal and temporal bones

37. Posterior View

38. • Warm and moisten air
• Lighten the skull
• Enhance voice resonance
Frontal Sinus
Ethmoid Sinus
Sphenoid Sinus
Maxillary Sinus

39. Cervical Vertebrae (7)
Thoracic Vertebrae (12)
Lumbar Vertebrae (5)
Sacrum 1 (5 fused)
Coccyx 1 (4 fused)
The Vertebral Column

40. Cervical Vertebrae

43. Sacrum & Coccyx

44. Sternum
True Ribs (7)
False Ribs (3)
Floating Ribs (2)
The Thoracic Cage

45. Bones of the Pectoral Girdle

46. Humerus
Ulna
Radius
8 Carpals
14 Phalanges
5 Metacarpals

50. CARPAL BONES
The Carpus (wrist) consists of 8 carpal bones:
They are arranged in two transverse rows of four bones each.
The Proximal row, from lateral to medial, are:
• Scaphoid (= boat like)
• Lunate (= moon-shaped)
• Triquetrum (three-cornered), and
• Pisiform (= pea-shaped)

51. CARPAL BONES CONT…
The distal row, from lateral to medial, are:
• Trapezium (= four-sided with no two sides parallel)
• Trapezoid (= four-sided with two sides parallel)
• Capitate (= head-shaped), the largest one
• Hamate (= hooked)

52. MNEMONIC FOR CARPAL BONES
Stop Letting Those People Touch The Cadaver’s Hand
Proximal Row Distal Row
Lateral Medial Lateral Medial
Scaphoid Lunate Triquetrum Pisiform Trapezium Trapezoid Capitate Hamate

53. HOW TO REMEMBER CARPAL BONES
Remember
 3tsp HCl (3tsp of HCl)
• 3tsp= trapezium, trapezoid, triquetral, scaphoid,
pisiform
• HCl= Hamate, Capitate, lunate

54. Pelvis

55. Ischium
Ilium
Acetabulum
Pubis
Ischium
Obturator
foramen
Pelvis (lateral view)

56. DIFFERENCE B/W MALE AND FEMALE
PELVIS
Male Pelvis
• Heavy and thick
• Pelvic brim is smaller
and heart-shaped
• Acetabulum is large
• Obturator foramen is
round
• Pubic arch ˂ 900
Female Pelvis
• Light and thin
• Pelvic brim is larger
and oval-shaped
• Acetabulum is small
• Obturator foramen is
round
• Pubic arch ˃ 900

57. Male Pelvic Girdle Female Pelvic Girdle

58. Patella
The Lower Limb
(Legs)
Femur
Tibia
Fibula
5 Metatarsals
14 Phalanges
7 Tarsals

62. metatarsals
phelangies
tarsals
metatarsals
phelangies
tarsals

64. TARSAL BONES
Tarsus (ankle) consists of 7 tarsal bones:
• Talus (= ankle bone)
• Calcaneus (= heel), the largest one
• Navicular (= like a little boat)
• Three Cuneiforms (= wedge-shaped), called first, second, and
third
• Cuboid (= cube-shaped)

65. ABNORMAL CURVES OF VERTEBRAL
COLUMN
• Scoliosis (= crooked) is a lateral bending of the vertebral column
usually in the thoracic region.
• Kyphosis (= hump) is an increase in the thoracic curve of the vertebral
column in which shoulder bends upward.
• Lordosis (= bent backward) may also called hollow back, is an increase
in the lumber curve.

66. • Spina bifida
• Is a congenital defect of the vertebral column in which
laminae of L5 and/or S1 fail to develop normally and unit at
the midline.
• The least serious form is called spina bifida occulta and
showing no symptoms but the presence of a small dimple.
• Other types of spina bifida involves the protrusion of
meninges and/or spinal cord and are collectively termed as
spina bifida cystica for the presence of cyst. If the sac
contains meninges and CSF, the condition is called spina
bifida with meningocele. If the sac contains meninges and
nerves, it is then called spina bifida with meningomyelocele.
• An increased risk of Spina bifida is associated with the
deficiency of vitamin B called folic acid.

67. 275 BONES
12 WEEKS (6-9
INCHES LONG)

68. cartilage
calcified
cartilage
bone
epiphyseal
plate
epiphyseal
line
Endochondral Ossification
2o ossification
center
Fetus: 1st
2 months
Adult
Childhood
Just before
birth

69. Osteoblast
Osteocyte
Osteoclast
Eats bone
Builds new bone
Mature bone cell

70. Bone Repair:
1. Electrical stimulation of the fracture site:
• Increases speed and completeness of healing
• The e- stimulation inhibits PTH and slow osteoclasts down
from reabsorbing bone
2. Ultrasound treatment:
• Daily treatments reduce healing time of broken bones by
25-35%
3. Free vascular fibular graft technique:
• Transplant fibula in arm
• Gives good blood supply not available in other treatments
4. Bone substitutes:
• Crushed bone from cadaver- but risk of HIV and hepatitis
• Sea bone- coral
• Artificial bone- ceramic

72. hematoma
callus bony callus
bone
remodeling

73. Diseases of the Skeletal System:
Osteoporosis- bone reabsorption
outpaces bone deposit; bones
become lighter and fracture easier
Factors:
• age, gender (more in women)
• estrogen and testosterone decrease
• insufficient exercise (or too much)
• diet poor in Ca++ and protein
• abnormal vitamin D receptors
• smoking

74. OSTEOPOROSIS
29 40 84 92

75. Rickets- vitamin D deficiency
Osteomalacia- soft bones, inadequate
mineralization in bones, lack of vitamin D
Pagets Disease- spotty weakening in the
bones, excessive and abnormal bone
remodeling
Rheumatoid arthritis- autoimmune
reaction
Diseases of the Skeletal System:

77. INQUIRY
http://www.youtube.com/watch?v=DSHoonPWwXQ
1. What is a fontanel?
2. How many bones in the adult skeleton?
3. What is the difference between the appendicular
and axial skeleton?
4. What is a meniscus?
5. Demonstrate adduction.
6. Weight bearing vertebrae are called?
7. What does an osteoclast do?
Extra Credit: 1-page reaction paper on bipedalism
and problems associated with our human frame.
Attach article. Turn in 1-week from today.

78. Bone anatomy
Most bones develop from cartilaginous ossification centres to form a diaphysis
(shaft), or epiphysis (end). During bone growth the diaphysis and epiphysis
are separated by the epiphyseal line (growth plate) which fuses later in life.
The zone adjacent to the growth plate on the diaphyseal side is called the
metaphysis.
Sesamoid
A sesamoid bone is a bone that ossifies within a tendon. The largest is the
patella. Sesamoids are also common at the first metatarsophalangeal joint
(big toe) and the first metacarpophalangeal joint (thumb).
Apophysis
An apophysis is a normal developmental outgrowth of a bone which arises
from a separate ossification centre, and fuses to the bone later in
development. An apophysis usually does not form a direct articulation with
another bone at a joint, but often forms an important insertion point for a
tendon or ligament.
Occasionally an apophysis can persist into adult life and if injured may
become symptomatic. The many apophyses in the body have variable
appearances and are often mistaken for fractures.

79. BONES TYPES
• Long bones comprise diaphysis, metaphysis and epiphysis
• The growth plate separates the metaphysis from the epiphysis
until fusion in adult life
• A sesamoid is a bone that ossifies within a tendon
• An apophysis is a normal bony outgrowth of a bone

82. •

83. •

84. 6 TYPES OF BONES
• Long Bones (greater length than width; femur)
• Short Bone (equal in length and width; carpal)
• Flat Bone (Thin and composed of two nearly parallel plates of
compact bone tissue enclosing a layer of spongy bone tissue;
sternum)

85. •

86. •

87. •

88. •