Chapter 7
THE SKELETAL SYSTEM
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Introduction
• Skeleton: supporting structure
• Bones and associated cartilage, tendons
and ligaments
• Works with muscles for movement
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Introduction (cont’d.)
• Mineral salts form the inorganic matrix of
bone
• Leonardo da Vinci: constructed first correct
illustrations of all bones
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THE FUNCTIONS OF THE SKELETAL SYSTEM
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The Functions of the Skeletal
System (cont’d.)
•
•
•
•
•
Supports surrounding tissues
Protects vital organs and soft tissues
Provides levers for muscles to pull on
Manufactures blood cells
Stores mineral salts
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The Functions of the Skeletal
System (cont’d.)
• Cartilage
– Connective tissue
– Environment in which bone develops in fetus
– Found at ends of bones and in joints
• Ligaments
– Attach bones to bones
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The Functions of the Skeletal
System (cont’d.)
• Tendons
– Attach muscles to bones
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THE GROWTH AND FORMATION OF BONE
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Introduction
• A three-month fetal skeleton is completely
formed (cartilage)
• Ossification and growth begin
• Longitudinal growth continues until:
– 15 years of age for girls
– 16 years of age for boys
• Bone maturation until 21 years of age
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Deposition of Bone
• Osteoblasts: embryonic bone cells
• Osteocytes: mature osteoblasts
• Strain on bone (exercise) increases bone
strength
• Osteoclasts: bone reabsorption and
remodeling
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Types of Ossification
• Intramembranous
– Dense connective membranes replaced by
calcium salts
– Cranial bones
• Endochondral
– Bone develops inside cartilage environment
– All other bones of the body
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Maintaining Bone
• Endocrine system control
– Calcium storage
– Blood calcium levels
– Excretion of excess calcium
• Parathormone: calcium release
• Calcitonin: calcium storage
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THE HISTOLOGY OF BONE
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Introduction
• Two types of bone: compact and
cancellous (spongy)
– Osteocytes same but arrangement of blood
supply different
– Cancellous has bone marrow
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The Haversian System of
Compact Bone
• Clopton Havers: histology of compact bone
• Haversian canals: run parallel to surface
– Surrounded by concentric rings of bone
– Lacunae: cavity containing osteocyte
– Lacunae connected by canaliculi
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Cancellous Bone
• Trabeculae: meshwork of bone
• Spongy appearance created by trabeculae
• Bone marrow fills spaces between
trabeculae
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Bone Marrow
• Red marrow
– Hematopoiesis
– Ribs, sternum, vertebrae, pelvis
• Yellow marrow
– Fat storage
– Shafts of long bones
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THE CLASSIFICATION OF BONES BASED ON SHAPE
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Introduction
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Long Bones
• Length exceeds width
• Consist of
– Diaphysis: shaft
– Metaphysis: flared portion
– Epiphysis: extremity
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Long Bones (cont’d.)
• Structure of a
long bone
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Short Bones
• Not merely shorter versions of long bones
• Lack a long axis
• Somewhat irregular shape
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Flat Bones
• Thin bones found wherever need for
extensive muscle attachment
• Usually curved
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Irregular Bones
• Very irregular shape
– Example: vertebrae
• Spongy bone enclosed by thin layers of
compact bone
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Sesamoid Bones
• Small rounded bones
• Enclosed in tendon and fascial tissue
• Located adjacent to joints
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BONE MARKINGS
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Introduction
• Processes: projections
• Fossae: depressions
• Functions: muscle attachment, articulation,
passageways
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Processes
• Processes: projections from the surface
– Spine, condyle, tubercle, trochlea, trochanter,
crest, line, head, neck
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Fossae
• Fossae: depressions
– Suture, foramen, meatus, sinus, sulcus
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DIVISIONS OF THE SKELETON
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Divisions of the Skeleton
(cont’d.)
• Typically has 206 named bones
• Axial part
– Skull, hyoid, vertebrae, ribs, sternum
• Appendicular part
– Upper extremities or arms
– Lower extremities or legs
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Divisions of the Skeleton
(cont’d.)
• Adult human skeleton:
anterior view
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Divisions of the Skeleton
(cont’d.)
• Adult human skeleton:
posterior view
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THE AXIAL SKELETON
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The Cranial Bones
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•
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•
•
•
Frontal bone (1)
Parietal bones (2)
Occipital bone (1)
Temporal bone (2)
Sphenoid bone (1)
Ethmoid bone (1)
Auditory ossicles (6)
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The Facial Bones
•
•
•
•
•
•
Nasal bones (2)
Palatine bones (2)
Maxillary bones (2)
Zygomatic bones (2)
Lacrimal bones (2)
Nasal conchae (2)
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The Facial Bones (cont’d.)
• Vomer bone (1)
• Mandible (1)
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The Facial Bones (cont’d.)
• Bones of the
face and skull,
lateral view
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The Orbits
• Orbits: cavities enclose and protect the eyes
Area of Orbit Participating Bones
Roof
Frontal, sphenoid
Floor
Maxilla, zygomatic
Lateral wall
Medial wall
Zygomatic, greater wing of sphenoid
Maxilla, lacrimal, ethmoid
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The Nasal Cavities
• Nose framework surrounds the two nasal
cavities
Area of Nose
Participating Bones
Roof
Ethmoid
Floor
Maxilla, palatine
Lateral wall
Maxilla, palatine
Septum of medial wall Ethmoid, vomer, nasal
Bridge
Nasal
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The Foramina of the Skull
• Passageways for blood vessels and nerves
• Foramen magnum: spinal cord passage
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The Hyoid Bone
• No articulation with other bones
• Suspended by ligaments from styloid
process
• Supports the tongue
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How to Study the Bones of the
Skull
• Refer to color illustrations in textbook
• Use a model of a human skull
• Search for sutures as a guide
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The Torso or Trunk
• Vertebrae
– Seven cervical
– Twelve thoracic
– Five lumbar
– Sacrum
– Coccyx
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The Thorax
• Thorax or rib cage made up of:
– Sternum
– Costal cartilages
– Ribs
– Bodies of thoracic vertebrae
• Encloses and protects heart and lungs
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The Thorax (cont’d.)
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The Sternum
• Breastbone
• Has three parts
– Manubrium
– Gladiolus
– Xiphoid process
• Attachment for diaphragm and rectus abdominis
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The Ribs
• Also called costae
• Attach posteriorly to thoracic vertebrae
• 12 pairs
– True ribs, false ribs, floating ribs
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THE APPENDICULAR SKELETON
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The Bones of the Upper
Extremities
• Shoulder girdle: clavicle and scapula
• Arm
– Upper arm: humerus
– Forearm: ulna and radius
– Wrist: carpals
– Hand: metacarpals (5/hand)
– Fingers: phalanges (14/hand)
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The Bones of the Upper
Extremities (cont’d.)
• Bones of the wrist
and hand
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The Bones of the Lower
Extremities
• Pelvic girdle: ischium, ilium, pubis
• Leg
– Upper leg: femur
– Lower leg: patella, tibia, fibula
– Foot
• Tarsals
• Metatarsals (5/foot)
• Phalanges (14/foot)
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The Bones of the Lower
Extremities (cont’d.)
• Right ankle and
foot, lateral view
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The Bones of the Lower
Extremities (cont’d.)
• Right ankle and foot,
superior view
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THE ARCHES OF THE FOOT
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The Arches of the Foot (cont’d.)
• Enable foot to bear weight while standing
and to provide leverage while walking
• Medial longitudinal: highest
• Lateral longitudinal
• Transverse
• Pes planus: flat foot
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Animation – Twisting Force
• The following animation illustrates the damage that can
occur to muscle, bone, or joint due to a twisting action
Click Here to Play Twisting Force Animation
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to a publicly accessible website, in whole or in part.
Animation – Direct Force
• The following animation illustrates a fracture due
to direct force to the bone from another object.
Click Here to Play Direct Force Animation
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to a publicly accessible website, in whole or in part.
Summary
• Listed the functions of the skeletal system
• Described the process of growth and
formation of bone
• Described the structure of compact and
cancellous bone
• Defined the various processes and fossae
associated with bones
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Summary (cont’d.)
• Named the bones of the axial and
appendicular skeleton
• Described the arches of the foot
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