The SKELETAL System
The framework of 206 bones,
ligaments and cartilage.
Functions of the Skeletal System
Types of Bone Cells
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Osteoblasts form bone by depositing
minerals and collagen fibers.
Osteocytes maintain bone tissue and are
known as the bone cells.
Osteoclasts break down bone tissue by
secreting enzymes to destroy bone
tissue.
Bone Cells
Ossification
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The process by which bones form in the
body (Osteogenesis)
Intramembranous Ossification
– Convert membrane models to bone
– (Periosteum – growth in width)
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Endochondral Ossification
– Convert cartilage to bone
– (Epiphyseal plate - growth in length)
Intramembranous Ossification
Location: Skull
Endochondral Ossification
Occurs in Long Bones
Epiphyseal
Plate
Homeostasis and Bone Remodeling
Bones constantly undergo
ossification and remodeling.
• Replaces older bone matrix with
new bone matrix:
– bone reabsorption (osteoclasts)
– bone deposition (osteoblasts)
• Allows injured or worn bone to be
replaced.
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Long Bone Anatomy
Long Bone Features
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Periosteum – the outer connective
tissue membrane covering the outer
surface of most bones.
Diaphysis – shaft or midsection of the
bone which contains bone marrow and
adipose tissue.
Epiphysis – the rounded ends of a long
bone.
Long Bone Features, p. 2
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Medullary Cavity – a central cavity in
the diaphysis which contains red bone
marrow and yellow bone marrow.
Red Bone Marrow – composed of soft,
gel-like hematopoietic tissue that fills
the diaphysis and produces red blood
cells (erythrocytes), white blood cells
(leukocytes), and platelets
(thrombocytes)
Long Bone Features
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Yellow Bone Marrow – adipose tissue
that will replace the red bone marrow
in the diaphyses (shafts) of long bones
during adulthood.
Long Bone Features
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Endosteum – the lining of the
medullary cavity.
Articular Cartilage – hyaline cartilage
found on the ends of long bones
(epiphyses) to reduce friction during
joint movement.
Compact Bone – densely packed
osteocytes to provide strength to the
bone.
Long Bone Features
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Spongy Bone – loosely-packed
osteocytes which help to reduce the
weight of the bone and form the red
marrow.
Compact Bone – densely-packed
osteocytes to provide strength to the
bone by forming a shell around the
spongy bone.
Let’s Quiz
Answers
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Articular Cartilage
Spongy Bone
Compact Bone
Medullary Cavity
Yellow Marrow
Periosteum
Proximal Epiphysis
Diaphysis
Distal Epiphysis
Shapes of Bones
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FOUR Categories of Bone Shapes
Long Bones
Short Bones
Flat Bones
Irregular Bones
Shapes of Bones
Long Bones
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Greater length than width
Have a distinct diaphysis and a variable
number of epiphysis
Slightly curved for strength
Examples: humerus, ulna, radius,
femur, tibia, fibula, metacarpals,
metatarsals, phalanges
Short Bones
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Cube-shaped bones
Nearly equal in length and width
Spongy texture on inside of the bone
Examples: carpal and tarsal bones
Flat Bones
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Generally thin and flat (plate-like)
Compact bone on anterior and posterior
surfaces with spongy bone in the middle
Provides protection to organs
Large surface area for muscle attachment
Examples: cranial bones, sternum, scapula,
ribs
Irregular Bones
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Complex-shaped bones
Cannot be classified into other
categories
Vary in the amount of spongy and
compact bone
Examples: vertebrae, facial bones,
patella
Classification of Bones
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Compact Bone (Dense Bone)
– little space between the solid components of bone
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Spongy Bone (Trabecular Bone)
– made up of an irregular network of thin plates of
bone with many intercellular spaces called
trabeculae (spicules)
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spaces between trabeculae filled with red bone marrow
responsible for hematopoiesis
Spongy Bone Structure
Compact Bone
Bone Markings
Refers to any bump,
groove, opening, or
depression associated
with a bone. They
have a names and
functions
Foramen
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An opening or
hole in a bone for
the passage of
nerves and/or
blood vessels.
Example:
Foramen
Magnum (spinal
cord)
Meatus
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A tube-like
passage within a
bone.
Example:
External Auditory
Meatus (green)
passageway for
sound.
Sinus
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A space within a
bone lined with
mucus membrane
that reduces the
weight of a bone.
Example:
Frontal Sinus
(green)
Fossa
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A depression or
groove in the bone.
Example:
Mandibular Fossa –
the depression
where the mandible
or jaw contacts the
skull.
Condyle
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A large rounded
prominence on a
bone.
Example: The
mandibular
condyle of the
jaw.
Tuberosity
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A large, rounded,
usually roughened
area for the
attachment of
tendons and
ligaments.
Example: Tibial
Tuberosity for
attachment of
patellar tendon
Trochanter
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A large blunt
process found
only on the femur
for muscle
attachment.
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Example: The
greater trochanters
of the femurs.
Tubercle
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A small rounded
projection for
muscle
attachment.
Example – The
greater tubercle
of the humerus.
Process
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A growth or
extension projecting
from a bone used
for muscle
attachment or to
form a joint.
Example – the
mastoid process of
the temporal bone.
Fontanels
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Found only on the
infant skull, it is a
membrane-covered "soft
spot” where the bones
(sutures) have not fused.
The fontanelles allow
for growth of the brain
and skull during an
infant's first year.
Example – the anterior
fontanel.
Fontanels – Birth View
Sutures
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Strong, immovable
joints that are
formed as the
membranes in the
fontanels are
replaced by tough,
fibrous tissue.
Sutures hold the
cranial bones
together.
Example – coronal
suture
Sutures – Fetal View
2 Divisions of the Skeleton
The AXIAL skeleton and the APPENDICULAR skeleton
Axial Skeleton
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The axial skeleton
consists of 80 bones and
forms the skull,
vertebrae, rib cage, and
hyoid bone.
Appendicular Skeleton
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The appendicular
skeleton is composed
of 126 bones.
It helps in locomotion
(pelvic girdle and
lower limbs) and
manipulation of objects
in the environment
(pectoral girdle and
upper limbs).
The Axial Skeleton
Axial Skeleton
80 Bones
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Skull – Cranial and Facial Bones - 22
Hyoid Bone -1
Vertebral Column - 24
Sternum - 1
Ribs - 24
The Skull Bones
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Mandible
Maxilla
Zygomatic
Frontal
Parietal
Occipital
Temporal
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Sphenoid
Ethmoid
Facial Bones
Mandible
• Maxilla
• Zygomatic
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Cranial Bones (8)
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Frontal Bone
Parietal Bones (2)
Temporal Bones (2)
Occipital Bone
Sphenoid Bone
Ethmoid Bone
Hyoid Bone
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The hyoid bone is a
U-shaped bone
found superior to
the larynx.
It holds the tongue
in place and
provides for muscle
attaachment in the
neck.
Frontal Bone
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Forms the forehead, the roof of the
orbits (eye sockets) and most of the
anterior portion of the cranial floor
Temporal Bones (2)
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Form the inferior sides of the cranium
and part of the cranial floor
Temporal bone landmarks:
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Zygomatic Process
Mandibular Fossa
External Auditory Meatus
Mastoid Process
Styloid Process
Parietal Bones
Occipital Bone
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The posterior part and prominent
portion of the base of the cranium
Occipital bone landmarks:
– Foramen Magnum
– Occipital Condyles
– External Occipital Protuberance
Sphenoid Bone
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Bone situated in the middle part of the
base of the skull
Shaped like a bat
Only bone that connects to all other
cranial bones
Sphenoid bone landmarks:
– Body
– Greater Wings
- Sella Turcica
-Sphenoid Sinuses
Sphenoid Bone
Ethmoid Bone
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Light, spongy bone located in the anterior
floor of the cranium between the orbits
Makes up much of the structure of the nasal
cavity
Ethmoid bone landmarks:
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Lateral Masses (Labyrinths)
Ethmoid Sinuses
- Crista Galli
Perpendicular Plate
-Cribriform Plate
Superior Nasal Conchae
Middle Nasal Conchae
Ethmoid Bone
Zygomatic Bones (2)
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cheek bones
form the prominences of the cheeks and
the floor and outer walls of the orbits
Zygomatic bone landmarks:
– temporal processes
– zygomatic arches
Maxillary Bones (2)
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Pair of bones that unite to form the upper jaw
Articulate with every bone of the face except
the mandible
Maxillary bone landmarks:
– Alveolar Processes
– Alveoli
– Palatine Processes - horizontal projection from the
maxillae that forms the anterior three fourths of
the hard palate
– Cleft Palate
– Cleft Lip
Cleft Palate & Cleft Lip
Facial Bones
Sagittal Section
Mandible (Lower Jaw) Bone
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Largest and strongest bone in the face
The only moveable skull bone
Articulates with the temporal bone to
form the Temporal Mandibular Joint
(TMJ)
The Appendicular Skeleton
Appendicular Skeleton
126 Bones
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clavicle
scapula
humerus
ulna
radius
carpals
metacarpals
phalanges
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pelvis
femur
patella
tibia
fibula
tarsals
metatarsals
phalanges
The Pectoral Girdle
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Clavicles (2)
(collar bones)
Scapulae (2)
(shoulder blades)
The Upper Limb
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Humerus (1)
(arm bone)
Radius (1)
(lateral foream)
Ulna (1)
(medial forearm)
Carpals (8)
(wrist)
Metacarpals (5)
(hand bones)
Phalanges (14)
(fingers)
Pelvis (Os Coxae)
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Ilium (2)
Ischium (2)
Pubis (2)
Lower Limb
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Femur (1)
(thigh bone)
Patella (1) (knee cap)
Tibia (1)
(shin bone)
Fibula (1)
(lower leg bone)
Tarsals (7)
(ankle bones)
Metatarsals (5)
(foot bones)
Phalanges (14) (toes)
The Vertebral Column
(Spine)
Composed of 33 (26) bones
• Encloses and protects the
spinal cord
• Supports the head
• Lower vertebrae supports the
weight of the entire upper body
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Vertebrae
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Bones of the vertebral column
Cervical vertebrae (7) - neck
Thoracic vertebrae (12) - ribs
Lumbar vertebrae (5) - lower back
Sacral vertebrae (5) - pelvic bones
Coccygeal vertebrae (4) - tail bone
Intervertebral Foramina - openings
between the vertebrae for nerve exit
Vertebral Column
Joints (Articulations)
The point of contact between bones,
between bones and cartilage, or
between bones and fibrous tissue
Structural Classification of
Joints
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Classification of which tissues are
holding the bones together:
Fibrous Joints
– held together by fibrous connective tissue
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Cartilaginous Joints
– held together by cartilage
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Synovial Joints
– joint enclosed within a synovial or joint
capsule
Fibrous Articulations
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Example:
Sutures between
the cranial bones
Cartilaginous Articulations
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Examples:
Intervertebral discs
formed by cartilage
between the
vertebrae.
Synovial Joints
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Example:
Knee Joint
Functional Classification of
Joints
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Based on the degree of movement at a
joint.
Synarthroses – No movement at the
joint.
Amphiarthroses –Small or slight
movement at the joint.
Diarthroses – Freely moveable joints.
Synarthrotic Joints
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Example:
Sutures
Amphiarthrotic Joints
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Example:
Intervertebral Disks
Symphysis Pubic
Diarthrotic Joints
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Examples:
Elbow
Shoulder
Diseases and Disorders
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Herniated disk
Osteoarthritis
Osteoporosis
Scoliosis
Kyphosis
Lordosis
Spina bifida
RA (Rheumatoid
arthritis)
Intervertebral Discs
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Discs of fibrocartilage found between
the vertebrae from C1 to the sacrum
Functions to absorb shock
Allows for the multi-directional motion
between each vertebrae
– Annulus Fibrosis - outer fibrous ring
– Nucleus Pulposus - inner, soft pulpy
portion of the intervertebral discs
Herniated Discs
(Slipped Discs)
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Rupture of the fibrocartilage discs
Usually caused by compression forces
Usually occurs between L4 and L5 or L5 and
the 1st Sacral Vertebrae
Disc protrudes and exerts pressure on spinal
nerves
To decrease risk of herniated discs:
– 1. maintain optimal body weight
– 2. strengthen abdominal muscles
– 3. increase lower back flexibility
Herniated Disc
Osteoarthritis
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Degenerative joint disease associated with
aging or with trauma
Characteristics:
– degeneration of articular cartilage
– development of bone spurs
– usually effects large joints (knees, hips, etc)
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Treatment:
– rest
– removal of bone spurs
– joint replacement
Osteoarthritis
Osteoporosis
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Decrease in
bone mass
and increased
susceptibility
to fractures.
Osteoporosis
Contributing Factors
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Decreased estrogen production
Poor nutritional status
Low activity levels
Weight
Smoking
Drugs and alcohol consumption
Gender/race/hereditary factors
Osteoporosis - Treatment
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Calcium supplementation
Estrogen Replacement Therapy
Weight-bearing exercise
Steroid treatment therapy
Spina Bifida
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congenital defect where the neural arch
fails to unit
usually involves the lumbar vertebrae
symptoms may be mild to severe
– usually results in paralysis
– partial or complete loss of bladder control
– absence of reflexes
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can be diagnosed during pregnancy by
sonography, amniocentesis, blood tests
Spina Bifada
Abnormal Curvatures of the
Spine
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Scoliosis - lateral curvature of the spine
– usually in thoracic and lumbar region
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Kyphosis - hunchback/humpback
– exaggeration of thoracic curvature
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Lordosis - swayback (sprinters butt)
– exaggeration of lumbar curvature
Abnormal Curvatures
Scoliosis
Scoliosis
Kyphosis
Lordosis (swayback)
Rheumatoid Arthritis
Rheumatoid arthritis is an
autoimmune disease in which the
body’s immune system – which
normally protects its health by
attacking foreign substances like
bacteria and viruses – mistakenly
attacks the joints.
The cause of RA is not yet fully understood, although
doctors do know that an abnormal response of the
immune system plays a leading role in the
inflammation and joint damage that occurs.
Rheumatoid Arthritis