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The Skeletal System
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Skeleton: Overview
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Functions of the Skeleton
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Support
Protection of internal organs
Blood cell production- in red marrow
Storage- fat and minerals (calcium
and phosphorous
Movement
Skeleton: Overview
o Classification
• Long – longer than
they are wide
• Short – cube
shaped
• Flat – plate-like,
with broad
surfaces
• Irregular – varied
shapes
• Round – circular in
shape
Fig 6.1
Skeleton: Overview
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Anatomy of a Long Bone
• Periosteum – tough,
connective tissue
covering
• Epiphysis – expanded
portion at the ends of
bones
• Diaphysis – portion
between the epiphyses
• Medullary cavity – hollow
portion of diaphysis
containing yellow
marrow
• Articular cartilage – layer
of hyaline cartilage
where bones join
together
• Endosteum – lines the
medullary cavity and the
spaces of spongy bone
Skeleton: Overview
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Compact Bone
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Lacunae – contain bone cells (osteocytes)
Lamellae – concentric layers of matrix containing
collagen fibers and mineral salts
Blood vessels and nerves enter the central canal
Spongy Bone
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Contains bony bars and plates called trabeculae
Trabeculae follow lines of stress, giving bones strength
Fig 6.2b
Skeleton: Overview
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Bone Growth and Repair
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Osteoprogenitor cells – unspecialized
cells
Osteoblasts – bone forming cells
Osteocytes – mature bone cells
Osteoclasts – break down bone
Skeleton: Overview
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Bone Development and Growth
Ossification – formation of bone
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Epiphyseal plate
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Intramembranous ossification
Bone forms between two sheets of fibrous
connective tissue
Form bones of the skull
Endochondral ossification
Form most bones of the human body
Hyaline cartilage models are replaced by
bone
Band of cartilage in the epiphyses of long bones
Long bone growth continues until plate is
ossified
Appositional growth – increase in bone
diameter
Fig 6.3
Skeleton: Overview
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Remodeling of Bones
Bone is continually being broken down
and built up again
Osteoclasts remove worn cells and
deposit calcium in the blood
Osteoblasts remove calcium from the
blood and form new bone
Three important hormones regulating
bone growth
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Parathyroid hormone
Calcitonin
Growth hormone
Skeleton: Overview
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Bone Repair
Required after it fractures (breaks)
Steps involved in bone repair
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Hematoma
Fibrocartilaginous callus
Bony callus
Remodelling
Naming of fractures
Complete – bone is broken through
Incomplete – bone is not separated into two parts
Simple – does not pierce the skin
Compound – pierces the skin
Impacted – broken ends are wedged into each other
Spiral – ragged break due to twisting of bone
Reduction – repair of a fracture
Closed reduction – re-aligning bone fragments
without surgery
Open reduction – surgical repair of the bone
using plates, screws, or pins
Fig 6.4
Table 6.1
Fig 6.5
Axial Skeleton
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Lies in the midline of the body
Bones of the axial skeleton
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Skull
Hyoid bone
The vertebral column
The thoracic cage
Middle ear bones
Axial Skeleton
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Skull
Formed by the cranium and the facial
bones
Sinuses
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Air spaces within the bones
Lined by mucous membranes
Reduce the weight of the skull
Give the voice a resonant sound
Paranasal sinuses
Maxillary
Frontal
Sphenoidal
Ethmoidal
Mastoid sinuses
Fig 6.6
Axial Skeleton
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Bones of the Cranium
Protects the brain
Sutures – immovable joints
Composed of eight bones
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Frontal bone
Parietal bones
Occipital bone
Temporal bones
External auditory meatus
Mandibular fossa
Mastoid process
Styloid process
Zygomatic process
Sphenoid bone
Ethmoid bone
Crista galli
Cribriform plate
Perpendicular plate
Superior and middle nasal conchae
Fig 6.7a
Fig 6.7b
Fig 6.8a
Fig 6.8b
Axial Skeleton
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Bones of the Face
Maxillae
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Alveolar process
Palatine process
Palatine bones
Zygomatic bones
Lacrimal bones
Nasal bones
Vomer bone
Inferior nasal conchae
Mandible
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Mandibular condyle
Coronoid process
Skeletal Muscles of the Body
• Hyoid bone
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Superior to larynx
Only bone in the
body that does not
articulate with
another bone
Anchors the tongue
Site of attachment
for muscles
associated with
swallowing
Fig 6.5a
Axial Skeleton
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Vertebral Column (Spine)
Supports rib cage
Serves as a point of attachment for the
pelvic girdle
Protects the spinal cord
Consists of a series of separate bones
named for their location
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Seven cervical (neck)
Twelve thoracic (chest)
Five lumbar (lower back)
Five sacral
Three to five coccygeal
Normal curvatures
Fig 6.9
Axial Skeleton
Normal curvatures
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Cervical and lumbar – convex anteriorly
Thoracic and sacral – concave anteriorly
Provide support and balance
Abnormalities
Lordosis – exaggerated lumbar curvature
Kyphosis – increased roundness of the
thoracic curvature
Scoliosis – abnormal lateral curvature that
occurs most often in the thoracic region
Fig 6.10
Axial Skeleton
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Intervertebral Disks
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Prevent vertebrae from grinding against one
another
Absorb shock
Allow motion between vertebrae
Vertebrae
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Body – anterior portion
Vertebral foramin – canal for spinal cord
Bony projections serve as sites for muscle
attachment
Atlas (C1) – supports the head; allows head
movement up and down
Axis (C2) - serves as a pivot for the atlas; allows
head movement from side to side
Sacrum – fused sacral vertebrae; forms posterior
wall of the pelvic cavity
Coccyx – formed from a fusion of three to five
vertebrae
Fig 6.11
Axial Skeleton
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The Rib Cage
Protects the heart and lungs
Provides support for the bones of the pectoral
girdle
The ribs
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Twelve pair that connect to the thoracic vertebrae
True ribs – upper seven pairs connect directly to the
sternum by costal cartilages
False ribs – next five pair that attach indirectly to the
sternum or not at all (“floating” ribs)
The sternum
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Flat, blade-shaped bone
Composed of three bones that fuse
Manubrium
Body
Xiphoid process
Fig 6.12
Appendicular Skeleton
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Pectoral Girdle
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Clavicles
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Articulate medially with the manubrium
Only attachment to the axial skeleton
Serves as a brace for the scapula and
stabilizes the shoulder
Scapulae
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Spine
Acromion process
Coracoid process
Glenoid cavity
Fig 6.13
Appendicular Skeleton
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Upper Limb
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Humerus
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Long bone of the arm
Head articulates with the glenoid cavity of the
scapula
Greater and lesser tubercles serve as attachments
for muscles
Intertubercular groove holds a tendon from the
biceps brachii
Deltoid tuberosity attaches the deltoid
Capitulum articulates with the head of the radius
Trochlea articulates with the ulna
Coronoid fossa
Olecranon fossa
Fig 6.14
Appendicular Skeleton
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Radius
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Lateral side of the forearm
Head articulates with the capitulum of the humerus and
fits into the radial notch of the ulna
Radial tuberosity attaches a tendon from the biceps
brachii
Ulnar notch articulates with the head of the ulna
Styloid process attaches ligaments that run to the wrist
Ulna
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Longer bone of the forearm
Coronoid process articulates with the coronoid fossa
when elbow is flexed
Olecranon process articulates with the olecranon fossa
when the elbow is extended
Trochlear notch articulates with the trochlea of the
humerus
Head articulates with the ulnar notch of the radius
Styloid process attaches ligaments that run to the wrist
Fig 6.15
Appendicular Skeleton
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Hand
Wrist (carpus) contains eight small bones
Metacarpal bones form the palm
Phalanges
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Bones of the fingers
The thumb has only two phalanges (proximal
and distal)
The other fingers have three phalanges each
(proximal, middle, and distal)
Fig 6.16
Appendicular Skeleton
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Pelvic Girdle
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Coxal bones
Ilium
Ischium
Pubis
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Pubic symphysis
Obturator foramen
Gender differences
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Female
Female
Female
Female
Female
Female
has broader hips
pelvis is wider
inlet and outlet of the true pelvis are wider
pelvic cavity is more shallow
bones are lighter and thinner
pubic arch is wider
Fig 6.17
Appendicular Skeleton
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Lower Limb
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Femur
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Longest and strongest bone in the body
Head fits into acetabulum of coxal bone
Greater and lesser trochanters attach
muscles of the thigh and buttocks
Linea aspera attaches several muscles
Medial and lateral epicondyles attach
muscles and ligaments
Lateral and medial condyles articulate
with the tibia
Patellar surface articulates with the
patella
Fig 6.18
Appendicular Skeleton
• Tibia
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Medial bone of the
lower leg
Bears the weight from
the femur
Medial and lateral
condyles articulate
with the femur
Tibial tuberosity attach
patellar ligaments
Anterior crest
Medial malleolus
articulates with the
talus in the foot
• Fibula
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Lateral to the tibia
Stabilizes ankle
Fig 6.19
Appendicular Skeleton
• Foot
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Seven tarsal bones
Only the talus can
move freely
The calcaneus and the
talus support the
weight of the body
Five metatarsal bones
form the instep
The phalanges form the
toes
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Big toe has only two
Three each in other
toes
Fig 6.20
Joints (Articulations)
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Classification according to the
amount of movement
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Synarthrosis – immovable
Amphiarthrosis – slightly moveable
Diarthrosis – freely moveable
Classification according to
structure
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Fibrous
Cartilaginous
Synovial
Joints (Articulations)
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Fibrous – fibrous connective tissue
Fibrous connective tissue joins bone to
bone
Typically immovable
Sutures of the cranium
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Coronal – between the parietal bones and the
frontal bone
Lambdoidal – between the parietal bones and
the occipital bone
Squamosal – between each parietal bone and
each temporal bone
Sagittal – between the parietal bones
Joints formed by each tooth in its socket
Fig 6.7
Fig 6.8
Joints (Articulations)
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Cartilaginous
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Bones are joined by fibrocartilage or
hyaline cartilage
Usually slightly moveable
Synovial
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Bones do not touch each other
Bones are separated by a joint cavity
Usually freely moveable
Fig 6.21
Fig 6.22
Joints (Articulations)
Types of synovial joints
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Saddle joint
Ball-and-socket joint
Pivot joint
Hinge joint
Gliding joint
Condyloid joint
Fig 6.23
Joints (Articulations)
Movements permitted by synovial joints
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Angular movements
Flexion- decreasing angle or bending
Extension- increase angle or straightening
Adduction- towards the midline of body
Abduction- away from the midline of body
Joints- articulations
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Circular movements
Circumduction- conical movement
Rotation- single plane along longitudinal
axis
Supination
Pronation
Special movements
Inversion and eversion
Elevation and depression
Fig 6.24
Effects of Aging
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Cartilage and bone tend to
deteriorate
Articular cartilage may not function
properly, resulting in arthritis
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Osteoarthritis – deterioration of the
articular cartilage
Rheumatoid arthritis – synovial
membrane becomes inflamed
Gout – excessive buildup of uric acid
Osteoporosis is common
Homeostasis
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Functions of the Skeletal System
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Protection of internal organs
Bones assist in all phases of
respiration
Bones store and release calcium
Bones assist the lymphatic system
and immunity
Bones assist digestion
The skeleton is necessary to
locomotion
Homeostasis
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Functions of Other Systems
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The integumentary and the muscles
assist in protecting internal organs
The digestive system absorbs calcium
from food and the endocrine system
regulates the storage of calcium in
the bones
Movement of the bones is only
possible because of the contraction of
skeletal muscle