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Chapter 7
The Skeleton
Attachment scaffold for tendons, ligaments
and muscle
• Blood cell production
Types of Bone
• Long Bones – long, as in the arm (radius, ulna,
humerus) and thigh (femur)
• Short Bones – cube-like, as in wrists (carpal)
and ankles (tarsal)
• Flat Bones – plate-like, as in ribs, scapulae,
some skull bones (parietal)
• Irregular Bones – vertebrae, facial bones
• Round or Sesamoid Bones – small, round,
reside in tendons and next to joints – Knee cap
or patella is an example
Long Bones
Short Bones
Flat Bones
Irregular Bones
Sesamoid Bones
Parts of a Long Bone
Parts of a Long Bone
1. Epiphysis – wider, thicker region at the ends of
long bones. This usually forms a joint
(articulates) with another bone. Mostly made of
spongy bone
2. Diaphysis – the long bone shaft between two
3. Periosteum – the tough, vascular, fibrous
covering that is firmly attached to bone and
continues into tendons and ligaments. Helps
form and repair bone.
Parts of a Long Bone
4. Spongy Bone (cancellous bone)
mostly found in the epiphyses
Composed of loosely packed bone matrix
with gaps arranged in branching bony plates
called trabeculae.
Spongy bone is surrounded by a thin layer
of compact bone.
Parts of a Long Bone
6. Compact Bone
found in the wall of the bone, especially in the
Exists as a rigid long tube with a hollow called the
medullary cavity that is surrounded by a thin layer
of spongy bone
The thin layer of spongy bone is further lined with a
thin membrane called endosteum, which contains
bone-forming cells
The medullary cavity lined by the endosteum is filled
with soft connective tissue called marrow (usually
yellow; red marrow is usually found in spongy bone)
densely packed matrix, having no gaps
Red vs. Yellow Marrow
• Red blood cells, platelets and most white blood cells form
in red marrow; some white blood cells develop in yellow
marrow. The color of yellow marrow is due to the much
higher number of adipocytes. Both types of bone marrow
contain numerous blood vessels and capillaries.
• At birth, all bone marrow is red. With age, more and more
of it is converted to the yellow type. Adults have on average
about 2.6 kg of bone marrow, with about half of it being red.
• Red marrow is found mainly in the flat bones such as hip
bone , breast bone, skull, ribs, vertebrae and shoulder
blades, and in the cancellous ("spongy") material at the
proximal ends (epiphysis) of the long bones such as femur
and humerus.
• Yellow marrow is found in the hollow interior of the middle
portion of long bones (diaphysis).
A Journey into Compact Bone
(Haversian System)
Inside an Osteon
(Haversian System)
(Volkman’s canal)
Bone Development and Growth
• The skeletal system begins to develop in
the first few weeks of gestation
• Bones develop from connective tissue
such as cartilage. They can form in two
– Bone can develop in sheet-like layers of
connective tissue. These types of bone are
called Intramembranous bone.
– Bone can also develop from hyaline cartilage.
These bones are called Endochondral bone.
Intramembranous Ossification
Unspecialized (primordial or primitive) connective
tissue cells form membrane-like layers at sites of future
These primordial cells are supplied with O2 and
nutrition through a dense network of blood vessels and
the primordial cells actually form layers around the
blood vessels
The primordial cells grow large and specialize into
osteoblasts (bone-forming cells)
Osteoblasts secrete bone matrix around themselves,
creating spongy bone along the blood vessels
Further along in development some spongy bone can
become more dense and form compact bone
Endochondral Ossification
Most bones of the human skeleton are endochondral bones
Hyaline cartilage is what exists in the place of endochondral
bone early in development
Chondrocytes reside in lacunae and keep growing – their
lacunae grow as well
The matrix of the cartilage begins to disintegrate and the
chondrocytes die
As cartilage decomposes, a periosteum develops all round
Blood vessels and primordial connective tissue cells invade the
decomposing sites
Invading primordial cells differentiate into osteoblasts and start
forming spongy bone in place of the cartilage (just like
intramembranous bone formation)
Once the osteoblasts are completely trapped in their bony
matrix, they are called osteocytes
Osteoblasts from the periosteum deposit compact bone around
the spongy bone forming in the diaphysis – this thickens the
Endochondral Ossification, cont’d.
9. In long bones endochondral ossification
begins in the middle of the diaphysis – this is
called the primary ossification center
10. The epiphyses remain cartilaginous and
continue to grow
11. Eventually, spongy bone forms from the
cartilage in the epiphyses – this is called the
secondary ossification center
12. The primary ossification center (diaphysis)
and the secondary ossification centers
(epiphyses) are separated from each other
by a band of cartilage called the Epiphyseal
Growth at the Epiphyseal Plates
The chondrocytes in this plate are arranged in 4 layers
The first layer - layer closest to the end of the epiphyses
contain resting chondrocytes – they do not actively grow. This
layer also attaches the epiphyseal plate to the spongy bone
tissue of the epiphysis
The second layer contains chondrocytes dividing mitotically. As
they divide and form cartilaginous matrix around them, the
epiphyseal plate thickens
As the cells divide, the older chondrocytes enlarge and thicken
the plate even more – this forms the third layer
a. This activity lengthens the bone
b. Osteoblasts invade the growing plate and deposit a calcified
matrix around the older cells. The old cartilage cells die.
The fourth layer is basically made up of dead chondrocytes
trapped in a calcium matrix
Spongy bone and red marrow
Layers of the
Epiphyseal Plate
(1st Layer – resting chondrocytes)
(2nd Layer – chondrocyte mitosis)
(3rd Layer- chondrocytes enlarging)
(4th Layer)
Growth at the Epiphyseal Plates,
• Eventually, the fourth layer of the epiphyseal
plate is invaded by cells called osteoclasts,
which are large, multinucleated cells that are
created from the fusion of white blood cells
called monocytes
• Osteoclasts dissolve the calcified matrix with
lysosomes and phagocytize it
• That allows bone-forming osteoblasts to invade
the area and deposit bone matrix
• Osteoclasts also invade the center of the
diaphysis and dissolve some of the matrix. This
forms the medullary cavity
Growth Arrest
• The growth and ossification of the diaphysis and the
epiphysis continues until the two ossification centers
• Once the sites meet, bone growth is no longer possible
in that area
• Some hyaline cartilage remains at the end of epiphyses
as articular cartilage
• Children have epiphyseal plates in their bones –
indicating the possibility of further growth
Hydroxyapatite (a type of calcium phosphate)
Composition of Bone
33% Organic (protein)
67% inorganic
Bone Growth and Repair
• Balanced nutrition, adequate exposure to
sunlight, hormones and exercise all contribute to
bone growth and repair
– Calcium and phosphate salts
– Vitamin D3 (Cholecalciferol) – helps in calcium
absorption and is found in eggs, milk and foods
fortified with it
– Vitamin A is needed for osteoblast and osteoclast
– Vitamin C is needed for collagen development, so a
lack of it will inhibit bone development
– Vitamin K and B12 are needed for protein synthesis in
Bone Growth and Repair
• Growth hormone from the pituitary gland in the
brain stimulates division of chondrocytes in
epiphyseal plates
– Lack of it will cause pituitary dwarfism
– Too much will cause pituitary gigantism
– Some adults acquire an excess of growth hormone
and develop an exaggerated growth of certain body
parts like the jaw and hands – this is called
• Male and female hormones (estrogen and
testosterone) becomes active at puberty and
promote bone growth
• Physical exercise stimulates bone growth – this
is called hypertrophy and lack of exercise
causes bone loss – called atrophy
Calcium Resorption and Deposition
All through life, osteoclasts reabsorb bone and
octeoblasts replace bone
• When blood calcium levels are low, parathyroid
hormone stimulates osteoclasts to break down bone
tissue, releasing calcium from bone matrix into blood
• When there is too much calcium in the blood, the
thyroid gland releases calcitonin which stimulates
osteoblasts to pick up calcium from blood and store it
in bone matrix – thus forming new bone tissue
• Too much calcium in the blood also inhibits osteoclast
Bone and Joint Pathology
1) Rheumatoid arthritis - autoimmune disease,
affects smaller joints (e.g., hands)
2) Osteosarcoma - malignant bone tumor
3) Osteoporosis - porous bones
4) Gout - deposition of sodium urate crystals
5) Osteoarthritis - wear and tear arthritis, major
joints (e.g., knees)
• The most common form of
arthritis, osteoarthritis is also
known as degenerative joint
disease and occurs following
trauma to the joint, following
an infection of the joint or
simply as a result of aging.
There is emerging evidence
that abnormal anatomy may
contribute to early
development of
Osteogenesis Imperfecta
• Osteogenesis imperfecta (OI) literally means imperfectly
formed bones. People with OI have an error (mutation) in
the genetic instructions on how to make strong bones.
As a result, their bones break easily.
• One of the genes that tells the body how to make a
specific protein (type I collagen) is defective in people
with OI. Type I collagen is a major component of the
connective tissues in bones, ligaments, teeth, and the
white outer tissue of the eyeballs (sclera). As a result of
the defect, the body may not produce enough type I
collagen or it may produce poor quality collagen. The
result in both cases is the same: fragile bones that break
easily. However, the bones heal at a normal rate.
Osteogenesis Imperfecta
• Osteoporosis is a term that means "porous
bones." It is a skeletal disease affecting women
and men. Osteoporosis is a condition in which
bones have lost minerals—especially calcium—
making them weaker, more brittle, and
susceptible to fractures (broken bones). Any
bone in the body can be affected by
osteoporosis, but the most common places
where fractures occur are the back (spine), hips,
and wrists.
• Women are 4 times as likely than men to
develop it – usually after menopause
Bone Movement
More Joints
How many bones?
• There are 22 bones in the skull
– 8 bones form the cranium
– 14 bones make up the face
• 21 of the 22 bones are immobile and
• The 22nd, is the mandible (a facial bone) the only movable bone
Cranial Bones - 8
The cranium protects the brain
1 Frontal bone – contains frontal sinuse
2 Parietal bones (held together by the sagittal suture)
1 Occipital bone (Back of skull and base of cranium)
2 Temporal bones
1 Sphenoid bone – contains spenoid sinuses, sella
turcica, optic canal, foramen ovale, foramen rotundum
and foramen spinosum
• 1 Ethmoid bone – contains superior nasal conchae,
middle nasal conchae, perpendicular plate, crista galli,
cribiform plate, ethmoid sinuses, olfactory foramina
Facial Bones
• 2 Maxillary bones (upper jaw) – contains
maxillary sinuses
• 2 Palatine bones
• 2 Zygomatic bones
• 2 Lacrimal bones
• 2 Nasal bones
• 1 Vomer
• 2 Inferior nasal conchae
• 1 Mandible – contains mental foramen, ramus,
coronoid process, alveolar arch, mandibular
Cavities in bones
2 Frontal sinuses (Cranium)
2 Sphenoid sinuses (Cranium)
2 groups of Ethmoid sinuses (Cranium)
2 Maxillary sinuses (Face)
Foramina of Skull
Anterior Palatine Foramen
Palatine Process of Maxilla
Greater Palatine Foramen
Lesser Palatine Foramen
Pterygoid Processes of Sphenoid
Zygomatic Process
Squamous Part of Temporal
Mandibular Fossa
Styloid Process
Stylomastoid Foramen
Mastoid Process
Mastoid Foramen
Superior Nuchal Line
External Occipital Protruberance
Median Nuchal Line
Inferior Nuchal Line
Foramen Magnum
Condyloid Canal
Occipital Condyle
Hypoglossal Canal
Jugular Foramen
Carotid Canal
Foramen Spinosum
Foramen Ovale
Foramen Lacerum
Transverse Palatine Suture
Median Palatine Suture
Infantile Skull
• Not completely developed at birth – leaves
room for growth and molding
• Fibrous membranes called Fontanels
connect cranial bones
– Anterior fontanel-closes last (by end of year 2)
– Posterior fontanel – closes in month 2 after
– Sphenoid fontanel – closes in 3 months after
– Mastoid fontanel – closes at the end of the 1st
The Vertebral Column
The Vertebral Column
• Extends from skull to pelvis
• Made of bone called vertebrae
that are separated by discs of
• Provides support as well as
• An adult has 26 bones in the
7 cervical
12 thoracic
5 lumbar
sacral (These are 5 fused vertebrae
and counted as 1)
– coccyx region (These are 4 fused
vertebrae and counted as 1)
Convex anteriorly
Concave anteriorly
Convex anteriorly
Concave anteriorly
• A normal column has four curvatures
which offer strength and resiliency
– Cervical curvature –secondary - develops
when baby learns to hold head up
– Thoracic curvature
– Lumbar curvature – secondary - develops
when child learns to stand up
– Pelvic curvature
Abnormal Curvatures
1) Kyphosis – Exaggerated thoracic
2) Lordosis – Exaggerated lumbar
3) Scoliosis - lateral bending of the
vertebral column
Kyphosis and Lordosis
This condition is also called roundback
This condition is also called swayback
Scoliosis – Abnormal Curvature
Congenital scoliosis is caused by defects in
the spine present at birth. This form of
scoliosis is also accompanied by other
disorders of various organs.
Neuromuscular scoliosis is caused by
problems with the nerves or muscles. They
are unable to support the spine in its normal
position. The most common causes of this
type of scoliosis are cerebral palsy (see
cerebral palsy entry) and muscular
dystrophy (see muscular dystrophy entry).
Degenerative scoliosis is caused by
deterioration of the bony material (discs)
that separate the vertebrae. Arthritis in the
spinal cord can also lead to degenerative
In four out of five scoliosis cases, however,
the cause is unknown. Such cases are
known as idiopathic scoliosis. Children with
idiopathic scoliosis have not suffered from
related disorders such as bone or joint
disease early in life. Some researchers
believe that the condition may be inherited,
but scientists have yet to find a gene
responsible for the disease.
• A single bone of the vertebral column is called a
• A typical vertebra is made up of a drum-like part
called the body – a longitudinal row of these
bodies support the head and trunk.
• There are intervertebral discs between the rough
surfaces of the bodies
• Adjacent bodies are joined by two types of
ligaments, one on the anterior side and one on
the posterior side
– The anterior longitudinal ligaments
– The posterior longitudinal ligaments
Vertebral Ligaments
1. Anterior longitudinal ligament
2. Posterior longitudinal ligament
Cervical Vertebrae
• These seven bones are the smallest of the vertebrae
that comprise the neck and support the head.
• The first vertebra is the atlas, which appears as a
bony ring and supports the head.
• The second vertebra is the axis, with its toothlike
dens that pivots within the atlas.
• Features that separate cervical vertebrae from the
rest are the bifid spinous processes and transverse
Notice how the dens of the
Axis pivots inside the atlas.
The Shape of the
rest of the
Cervical Vertebrae
vertebrae have
the smallest
bodies of all
Spina Bifida
• Often called open spine, spina bifida
affects the backbone and, sometimes, the
spinal cord. It is among the most common
severe birth defects in the United States,
affecting 1,500 to 2,000 babies (one in
every 2,000 live births)
• Spina Bifida means cleft spine, which is an
incomplete closure in the spinal column.
Spina Bifida
Thoracic Vertebrae
Thoracic Vertebrae
• Twelve thoracic vertebrae articulate
with the ribs.
• These bones are larger and stronger
than the cervical vertebrae.
Lumbar Vertebrae
The five massive
lumbar vertebrae
support the weight of
the body. They have
the largest bodies of all
Sacrum and Coccyx
Sacrum, Coccyx
• The sacrum is a triangular structure at the base of the vertebral
column made up of five vertebrae fused into one bone.
• The spinous processes of these vertebrae fuse to form a ridge
of tubercles that have dorsal sacral foramina along their sides.
• On the ventral surface of the sacrum, four pairs of pelvic sacral
foramina provide passageways for nerves and blood vessels.
• The coccyx is the lowermost portion of the vertebral column
and is composed of four fused vertebrae.
Thoracic Cage
The Thoracic Cage
The thoracic cage includes the ribs, thoracic vertebrae, sternum, and costal
It supports the pectoral girdle and upper limbs, functions in breathing, and
protects thoracic and upper abdominal organs.
Normally, there are 12 pairs of ribs that attach to the thoracic vertebrae.
The first seven pairs of ribs are true (or vertebrosternal) ribs that join the
sternum directly by their costal cartilages.
The remaining five pairs are false ribs: the first three pairs are
vertebrochondral ribs, and the last two pairs are floating ribs.
Features of a typical rib include a shaft, costal groove, anterior (sternal) end,
head, neck, and tubercle.
– The head articulates with the vertebrae; the tubercle articulates with the transverse
process of the thoracic vertebrae.
The sternum (breastbone) is located along the anterior midline of the thoracic
It consists of an upper manubrium, middle body, and lower xiphoid process.
Spinous Process
Articular facet
Neck of rib
Vertebral Foramen
Anterior (sternal) end of rib
Pectoral Girdle
Made up of four
2 clavicles and
2 scapulae
Superior border
Lateral border
Medial border
The scapulae are flat, triangular bones on either side of the upper back.
A spine divides the scapula into unequal portions.
The spine leads to the acromion process (articulates with clavicle) and coracoid
process (provides attachments for limb and chest muscles).
The glenoid cavity articulates with the head of the humerus.
• S-shaped
• Medial (Sternal) side
articulates with upper
side of manubrium
• Lateral side (acromial)
meets the acromion of
the scapulae
• Help hold shoulders in
• Break easily due to the
elongated S shape
Upper Limbs
Extends from scapula to elbow
The “head” fits into the glenoid cavity of scapula
It articulates with the scapulae at its head, with the radius at the capitulum, and
with the ulna at the trochlea.
Located on thumb side of the forearm
Partners up with a slightly longer bone – the ulna
Extends from elbow to wrist and crosses over the ulna
On the proximal end (elbow end) it has a wrench-like opening called the trochlear
(semilunar) notch which articulates with the trochlea of the humerus
The olecranon process lies above the trochlear notch and the coronoid process
lies below the trochlear notch - these help with movement of upper arm at the
At the distal end, the “head” articulates with the ulnar nothch of the radius and
also is separated by a cartilaginous disc from the triquetrum one of the carpals
Hand and wrist
The wrist of the hand is made up of eight carpal bones bound into a carpus.
The framework of the hand is made up of five metacarpal bones.
The fingers are composed of three phalanges in each finger except the thumb,
which lacks the middle phalanx.
Radius and Ulna
Hand and Wrist
Pelvic Girdle
• The pelvic girdle consists of the two coxal bones and the sacrum; it supports
the trunk of the
body on the lower limbs.
• The pelvic girdle supports and protects the lower abdominal and pelvic
• Each Coxal bone is made up of three bones: iilium, ischium, and pubis, that
are fused in the region of the acetabulum, the cuplike depression that
articulates with the head of the femur.
• The ilium is the largest and most superior portion of the coxal bone and joins
the sacrum at the sacroiliac joint.
• Features of the ilium include the iliac crest, and anterior superior iliac spine.
• The ischium forms the L-shaped portion that supports weight during sitting.
• Fractures of the ischium include the ischial tuberosity and ischial spine.
• The pubis comprises the anterior portion of the coxal bones and articulates
at the symphysis pubis which has fibrocartilage.
• The large opening, the Obturator Foramen lies within each pubis.
• The greater pelvis is above the pelvic brim and the lesser pelvis is below it.
• There are structural differences between males and female pelves
Pelvic Girdle
Pelvic Girdle – Male vs. Female
The Coxa
The Lower Limb
The femur, or thighbone, extends from the hip to the knee and is the
longest bone in the body.
Its head articulates with the acetabulum; it articulates with the tibia at
the medial and lateral condyles.
Other features of the femur include the fovea capitis, neck, and greater
and lesser trochanters.
The patella (kneecap) is located in the tendon that passes over the
The tibia (shinbone) supports the weight of the body and articulates
with the femur (medial and lateral condyles) and with the tarsal bones
of the foot.
Its anterior tibial tuberosity is the point of attachment for the patellar
Other features of the tibia include the medial malleolus (inner ankle).
The fibula is a slender bone lying lateral to the tibia; it does not bear
body weight.
The lateral malleolus forms the lateral ankle.
Foot and ankle
Articulates with
acetabulum of coxal bone
Fibula and Tibia
(Lies lateral to tibia)
(The lateral malleolus forms
the lateral ankle.)
(The medial
malleolus forms the
lateral ankle.)
Foot and Ankle
• The ankle is composed of seven tarsal bones, forming a
• The talus articulates with the tibia and fibula.
• The calcaneus supports the body weight.
• The instep of the foot consists of five metatarsal bones
and provides an arch.
• Each toe is made up of three phalanges, with the
exception of the great toe, which lacks a middle phalanx.
Foot and Ankle
The talus articulates with the tibia and fibula.
Foot and Ankle
3 Types of Levers
Lever in the Body
• The straightening of the upper limb at the
elbow – First class lever ( force-pivotresistance)
• The mandible being lowered and raised
within the temporal bone - Second class
lever (force-resistance-pivot)
• Bending of the arm at the elbow – Thirdclass lever (resistance-force-pivot)