complete lecture

1. Skeletal System
Anatomy & Physiology
Unit-IV
Wiqar ullah
Ikramullah

2. Objectives
At the end of this lecture the students will be
able to:
• Define skeletal system
• List the functions of the skeletal system
• Discuss the structure, types and functions of bones
• 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:
i. Skull
ii. Vertebral column
iii. Rib cage

3. Skeletal System
•The framework of bones and cartilage that protects
organs and allows movement is called the skeletal
system.

4. • Support- framework that supports body and
cradles its soft organs.
• Protection- 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.
• Detoxification: Temporarily stores heavy metals

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 to 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
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

12. 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.

13. Histology of bone tissue cont….
Four types of cells are present in bone tissue as:
1. Osteogenic Cells, almost all other connective tissues are formed.
 They are the only bone cells that undergo division.
 They differentiate into osteoblasts.
2. Osteoblasts these bone forming cells are responsible for the
deposition of both inorganic salts and osteoid (ORGANIC
COPMPONENTS)in bone tissue.
They are there fore present at sites where bone is growing ,repairing
or remodeling e.g.
In the deeper layer of periosteum
In the center of ossifications of immature bone .
In the end of diaphysis adjacent to the epiphyseal cartilages of long
bones
At the site of fracture

14. Histology of bone tissue cont….
3. Osteocytes
these are the mature cell that monitor and maintain bone
tissue and are nourished by tissue fluid in the canaliculi that
radiate from the central canal .
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.

15. 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)
Phalanges (28)

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)

28. 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.

29. 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.

30. 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

31. 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.

32. 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.

33. 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.

34. 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:

35. 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.

36. 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.

37. 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.

38. 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

40. Posterior View

41. Facial Bones
The facial skeleton (also known as the viscerocranium)
supports the soft tissues of the face.
It consists of 14 bones, which fuse to house the orbits of
the eyes, the nasal and oral cavities, and the sinuses.
The facial bones are:
Zygomatic (2) – forms the cheek bones of the face and
articulates with the frontal, sphenoid, temporal and
maxilla bones.
Lacrimal (2) – the smallest bones of the face. They form
part of the medial wall of the orbit.

42. Inferior nasal conchae (2) – located within the
nasal cavity, these bones increase the surface area of the
nasal cavity, thus increasing the amount of inspired air
that can come into contact with the cavity walls.
Palatine (2) – situated at the rear of oral cavity and
forms part of the hard palate.
Maxilla (2) – comprises part of the upper jaw and
hard palate.
Vomer – forms the posterior aspect of the nasal
septum.
Mandible (jaw) – articulates with the base of the
cranium at the temporomandibular joint (TMJ).

45. The Hyoid Bone
The hyoid, a horseshoe-shaped bone situated in the anterior
of the neck, between chin and thyroid, aids tongue
movement and swallowing.
The hyoid bone is a horseshoe shaped bone found in the
neck. Located anteriorly between the mandible and the
thyroid cartilage, the hyoid bone protects the esophagus
and also facilitates the wide range of muscle activity
required for speaking and swallowing. It is visible upon
extension of the neck.

46. The hyoid bone consists of a central body and two pairs of cornua,
or horns, termed greater and lesser cornua. The greater horns
project backwards from the body and provide a platform for key
muscles and ligaments to attach to including the stylohyoid and
throhyoid muscles.

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

48. Cervical Vertebrae

51. Sacrum & Coccyx

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

53. Bones of the Pectoral Girdle

54. Humerus
Ulna
Radius
8 Carpals
14 Phalanges
5 Metacarpals

58. 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)

59. 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)

60. 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

61. How to remember Carpal Bones
Remember
 3tsp HCl (3tsp of HCl)
 3tsp= trapezium, trapezoid, triquetral,
scaphoid, pisiform
 HCl= Hamate, Capitate, lunate

62. Pelvis

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

65. 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

66. Male Pelvic Girdle Female Pelvic Girdle

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

70. metatarsals
phelangies
tarsals
metatarsals
phelangies
tarsals

73. 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)

74. 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.

76. •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.

77. SPINA BIFIDA