Chapter 7
The Skeletal System
Introduction
• Skeleton - supporting structure
• Bones and associated cartilage, tendons
and ligaments
• Works with muscles for movement
• Mineral salts form the inorganic matrix of
bone
• Leonardo da Vinci - first correct
illustrations of all bones
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The Functions of the Skeletal
System
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Support surrounding tissues
Protect vital organs and soft tissues
Provide levers for muscles to pull on
Manufacture blood cells
Store mineral salts
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The Growth and Formation of
Bone
General Information
• A three-month fetal skeleton completely
formed (cartilage)
• Ossification and growth begin
• Longitudinal growth continues until
– 15 years of age - girls
– 16 years of age - boys
• Bone maturation until 21 years of age
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Deposition of the 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 the 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
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
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Long
Short
Flat
Irregular
Sesamoid
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Bone Markings
• Processes - projections from the surface
– spine, condyle, tubercle, trochlea, trochanter,
crest, line, head, neck
• Fossae - depressions
– suture, foramen, meatus, sinus, sulcus
• Functions - muscle attachment,
articulation, passageways
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Divisions of the Skeleton
The Axial Skeleton
Cranial Bones
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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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Facial Bones
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Nasal bones (2)
Palatine bones (2)
Maxillary bones (2)
Zygomatic bones (2)
Lacrimal bones (2)
Nasal conchae (2)
Vomer bone (1)
Mandible (1)
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The Orbits, Nasal Cavities, and
Foramina
• Orbits - cavities enclose and protect the
eyes
• Nose framework surrounds the two nasal
cavities
• Foramina
– 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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The Torso or Trunk
• Sternum
• Ribs - 12 pairs
– true ribs, false ribs, floating ribs
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The Torso or Trunk
• Vertebrae
– seven cervical
– twelve thoracic
– five lumbar
– sacrum
– coccyx
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The Appendicular Skeleton
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 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 Arches of the Foot
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Medial longitudinal - highest
Lateral longitudinal
Transverse
Pes planus - flat foot
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Animation
• The following animation illustrates the
damage that can occur to muscle, bone, or
joint due to a twisting action.
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Animation
• The following animation illustrates a
fracture due to direct force to the bone
from another object.
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