Chapter 8 Skeletal System

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Chapter 8Skeletal System
2
Introduction

• Skeletal tissues form bonesthe organs of the
  skeletal system
• The relationship of bones to each other and to
  other body structures provides a basis for
  understanding the function of other organ systems
• The adult skeleton is composed of 206 separate
  bones

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Divisions of Skeleton

• The adult skeleton is composed of 206 separate
  bones
• Axial skeleton
• 80 bones of the head, neck, and torso
• 74 bones that form the upright axis of the body
• 6 tiny middle ear bones
• Appendicular skeleton
• 126 bones that form the appendages to the axial
  skeleton
• The upper and lower extremities

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Axial Skeleton

• Facial bones
• Maxilla (2)
• Zygomatic (2)
• Nasal (2)
• Mandible
• Vomer
• Lacrimal (2)
• Palatine (2)
• Inferior nasal concha (2)

• Skull
• 28 bones in two major divisions
• Cranial bones
• Frontal
• Parietal (2)
• Temporal (2)
• Occipital
• Sphenoid
• Ethmoid

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Axial Skeleton

• Cranial Bones
• Frontal bone
• Forms the forehead and anterior part of the top
  of the cranium
• Contains the frontal sinuses
• Forms the upper portion of the orbits
• Forms the coronal suture with the two parietal
  bones

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Axial Skeleton

• Cranial bones (cont.)
• Parietal bones
• Form the bulging top of the cranium
• Form several sutures
• Lambdoidal suture with occipital bone
• Squamous suture with temporal bone
• Coronal suture with frontal bone
• Part of sphenoid

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Axial Skeleton

• Cranial bones (cont.)
• Temporal bones
• Form the lower sides of the cranium and part of
  the cranial floor
• Contain the inner and middle ears

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Axial Skeleton

• Cranial bones (cont.)
• Occipital bone
• Forms the lower, posterior part of the skull
• Forms immovable joints with three other cranial
  bones and a movable joint with the first
  cervical vertebra

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Axial Skeleton

• Cranial bones (cont.)
• Sphenoid bone
• A bat-shaped bone located in the central portion
  of the cranial floor
• Anchors the frontal, parietal, occipital, and
  ethmoid bones and forms part of the lateral wall
  of the cranium and part of the floor of each
  orbit
• Contains the sphenoid sinuses

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Axial Skeleton

• Cranial bones (cont.)
• Ethmoid bone
• A complicated, irregular bone that lies anterior
  to the sphenoid and posterior to the nasal bones
• Forms the anterior cranial floor, medial orbit
  walls, upper parts of the nasal septum, and
  sidewalls of the nasal cavity
• The cribriform plate is located in the ethmoid

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Axial Skeleton

• Facial bones
• Maxilla (upper jaw)
• Two maxillae form the keystone of the face
• Maxillae articulate with each other and with
  nasal, zygomatic, inferior concha, and palatine
  bones
• Forms parts of the orbital floors, roof of the
  mouth, and floor and sidewalls of the nose
• Contains maxillary sinuses

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Axial Skeleton

• Facial bones (cont.)
• Mandible (lower jaw)
• Largest, strongest bone of the face
• Forms the only movable joint of the skull with
  the temporal bone
• Zygomatic bone
• Shapes the cheek and forms the outer margin of
  the orbit
• Forms the zygomatic arch with the zygomatic
  process of the temporal bones

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Axial Skeleton

• Facial bones (cont.)
• Nasal bone
• Both nasal bones form the upper part of the
  bridge of the nose, whereas cartilage forms the
  lower part
• Articulates with the ethmoid bone, nasal septum,
  frontal bone, maxillae, and the other nasal bone

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Axial Skeleton

• Facial bones (cont.)
• Lacrimal bone
• Paper-thin bone that lies just posterior and
  lateral to each nasal bone
• Forms the nasal cavity and medial wall of the
  orbit
• Contains groove for the nasolacrimal (tear) duct
• Articulates with the maxilla and the frontal and
  ethmoid bones

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Axial Skeleton

• Facial bones (cont.)
• Palatine bone
• Two bones form the posterior part of the hard
  palate
• Vertical portion forms the lateral wall of the
  posterior part of each nasal cavity
• Articulates with the maxillae and the sphenoid
  bone

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Axial Skeleton

• Facial bones (cont.)
• Inferior nasal conchae (turbinates)
• Form lower edge projecting into the nasal cavity
  and form the nasal meati
• Articulate with ethmoid, lacrimal, maxillary, and
  palatine bones
• Vomer bone
• Forms posterior portion of the nasal septum
• Articulates with the sphenoid, ethmoid, and
  palatine bones and maxillae

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Axial Skeleton

• Fetal skull
• Characterized by unique anatomic features not
  seen in adult skull
• Fontanels or soft spots (4) allow skull to
  mold during birth process and permit rapid
  growth of brain (Table 8-5)

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Axial Skeleton

• Hyoid bone
• U-shaped bone located just above the larynx and
  below the mandible
• Suspended from the styloid processes of the
  temporal bone
• Only bone in the body that articulates with no
  other bones

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Axial Skeleton

• Vertebral column
• Forms the flexible longitudinal axis of the
  skeleton
• Consists of 24 vertebrae plus the sacrum and
  coccyx
• Segments of the vertebral column
• Cervical vertebrae, 7
• Thoracic vertebrae, 12
• Lumbar vertebrae, 5
• Sacrumin adult, results from fusion of five
  separate vertebrae
• Coccyxin adult, results from fusion of four or
  five separate vertebrae

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Axial Skeleton

• Vertebral column (cont.)
• Characteristics of the vertebrae
• All vertebrae, except the first, have a flat,
  rounded body anteriorly and centrally, a spinous
  process posteriorly, and two transverse processes
  laterally
• All but the sacrum and coccyx have vertebral
  foramen
• Second cervical vertebra has upward projection,
  the dens, to allow rotation of the head
• Seventh cervical vertebra has long, blunt spinous
  process
• Each thoracic vertebra has articular facets for
  the ribs

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Axial Skeleton

• Vertebral column (cont.)
• Vertebral column as a whole articulates with the
  head, ribs, and iliac bones
• Individual vertebrae articulate with each other
  in joints between their bodies and between their
  articular processes

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Axial Skeleton

• Sternum
• Dagger-shaped bone in the middle of the anterior
  chest wall made up of three parts
• Manubriumthe upper, handle part
• Bodythe middle, blade part
• Xiphoid processthe blunt cartilaginous lower
  tip, which ossifies during adult life

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Axial Skeleton

• Sternum (cont.)
• Manubrium articulates with the clavicle and first
  rib
• Next nine ribs join the body of the sternum,
  either directly or indirectly, by means of the
  costal cartilage

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Axial Skeleton

• Ribs (Figures 8-15 and 8-16)
• Twelve pairs of ribs, with the vertebral column
  and sternum, form the thorax
• Each rib articulates with the body and transverse
  process of its corresponding thoracic vertebra
• Ribs 2 through 9 articulate with the body of the
  vertebra above

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Axial Skeleton

• Ribs (cont.)
• From its vertebral attachment, each rib curves
  outward, then forward and downward
• Rib attachment to the sternum
• Ribs 1 through 8 join a costal cartilage that
  attaches it to the sternum
• Costal cartilage of ribs 8 through 10 joins the
  cartilage of the rib above to be indirectly
  attached to the sternum
• Ribs 11 and 12 are floating ribs, because they do
  not attach even indirectly to the sternum

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Appendicular Skeleton

• Upper extremity
• Consists of the bones of the shoulder girdle,
  upper arm, lower arm, wrist, and hand
• Shoulder girdle
• Made up of scapula and clavicle
• Clavicle forms only bony joint with trunk, the
  sternoclavicular joint
• At its distal end, clavicle articulates with the
  acromion process of the scapula

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Appendicular Skeleton

• Upper extremity (cont.)
• Humerus
• The long bone of the upper arm
• Articulates proximally with the glenoid fossa of
  the scapula and distally with the radius and ulna

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Appendicular Skeleton

• Upper extremity (cont.)
• Ulna
• Long bone found on little finger side of forearm
• Articulates proximally with humerus and radius
  and distally with a fibrocartilaginous disk

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Appendicular Skeleton

• Upper extremity (cont.)
• Radius
• Long bone found on thumb side of forearm
• Articulates proximally with capitulum of humerus
  and radial notch of ulna articulates distally
  with scaphoid and lunate carpals and with head
  of ulna

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Appendicular Skeleton

• Upper extremity (cont.)
• Carpal bones
• Eight small bones that form wrist
• Carpals are bound closely and firmly by ligaments
  and form two rows of four carpals each
• Proximal row is made up of pisiform, triquetrum,
  lunate, and scaphoid
• Distal row is made up of hamate, capitate,
  trapezoid, and trapezium
• The joints between radius and carpals allow wrist
  and hand movements

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Appendicular Skeleton

• Upper extremity (cont.)
• Metacarpal bones
• Form framework of hand
• Thumb metacarpal forms the most freely movable
  joint with the carpals
• Heads of metacarpals (knuckles) articulate with
  phalanges

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Appendicular Skeleton

• Lower extremity
• Consists of the bones of hip, thigh, lower leg,
  ankle, and foot

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Appendicular Skeleton

• Lower extremity (cont.)
• Pelvic girdle is made up of the sacrum and the
  two coxal bones, bound tightly by strong
  ligaments
• A stable circular base that supports the trunk
  and attaches the lower extremities to it
• Each coxal bone is made up of three bones that
  fuse together
• Iliumlargest and uppermost
• Ischiumstrongest and lowermost
• Pubisanteriormost

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Appendicular Skeleton

• Lower extremity (cont.)
• Femurlongest and heaviest bone in the body
• Patellalargest sesamoid bone in the body
• Tibia
• The larger, stronger, and more medially and
  superficially located of the two leg bones
• Articulates proximally with the femur to form the
  knee joint
• Articulates distally with the fibula and the
  talus
• Fibula
• The smaller, more laterally and deeply placed of
  two leg bones
• Articulates with tibia

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Appendicular Skeleton

• Lower extremity (cont.)
• Foot
• Structure is similar to that of the hand, with
  adaptations for supporting weight
• Foot bones are held together to form spring
  arches
• Medial longitudinal arch is made up of calcaneus,
  talus, navicular, cuneiforms, and medial three
  metatarsals
• Lateral longitudinal arch is made up of
  calcaneus, cuboid, and fourth and fifth
  metatarsals

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Skeletal Differences in Men and Women

• Male skeleton is larger and heavier than female
  skeleton
• Pelvic differences
• Male pelvisdeep and funnel-shaped with a narrow
  pubic arch
• Female pelvisshallow, broad, and flaring with a
  wider pubic arch

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Cycle of Life The Aging Skeleton

• Aging changes begin at fertilization and continue
  over a lifetime
• Changes can be positive or negative
• Normal bone development is a skeletal aging
  process
• Intramembranous ossification
• Endochondral ossification
• Appearance of ossification centers and closure of
  epiphyseal plates can be used to estimate
  potential growth and height

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Cycle of Life The Aging Skeleton

• Characteristics of bone during age
• Bone produced early in life is properly calcified
  but not brittle
• Osteoblastic activity during early periods of
  bone remodeling results in deposition of more
  bone than is resorbed
• Prior to puberty results in growth of bones
• After puberty and until early thirties, replaced
  bone is stronger

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Cycle of Life The Aging Skeleton

• Negative outcomes of skeletal aging begin between
  30 and 40 years of age
• Decrease in osteoblast numbers with production of
  lower quality matrix
• Increase in osteoclast numbers and activity with
  increased bone loss
• Mature osteocytes coalesce and shrink, producing
  a honeycomb of tiny holes in the compact bone

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Cycle of Life The Aging Skeleton

• Negative outcomes (cont.)
• Skeleton as a whole loses strength, and fracture
  risk increases
• Decrease in number of trabeculae in spongy bone
  in vertebral bodies and other bones results in
  spontaneous as well as compression fractures
• Overall height decreases beginning at about age
  35
• Osteoporosis is a common and very serious bone
  disease in old age

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The Big Picture

• Skeletal system is a good example of increasing
  structural hierarchy in the body
• Skeletal tissues are grouped into discrete
  organsbones
• Skeletal system consists of bones, blood vessels,
  nerves, and other tissues grouped to form a
  complex operational unit
• Integration of skeletal system with other body
  organ systems permits homeostasis to occur
• Skeletal system is more than an assemblage of
  individual bonesit represents a complex and
  interdependent functional unit of the body

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Mechanisms of DiseaseBone Fractures

• Fracture defined as partial or complete break in
  continuity of a bone
• Mechanical stress and traumatic injury are most
  common causes
• Pathological or spontaneous fractures occur in
  absence of trauma
• Stress fractures may not be apparent in clinical
  examination or standard x-ray images but can be
  seen in bone scans
• Bone damage is microscopic
• Caused by repetitive trauma (e.g., marathon
  runners)

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Mechanisms of DiseaseBone Fractures

• Fracture defined (cont.)
• Displaced, open or compound fracturesdo not
  produce a break in the skin and pose less danger
  of infection
• Nondisplaced, closed or simple fracturesdo not
  produce a break in the skin and pose less danger
  of infection
• Fracture types
• Impactedone end of fracture driven into
  diaphysis of other fragment
• Completebreak extends across entire section of
  bone
• Incompletesome fracture components still
  partially joined
• Dentatefracture components jagged and fit
  together like teeth on a gear
• Comminutedcrushed, small, crumbled bone
  fragments near fracture

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Mechanisms of DiseaseBone Fractures

• Fracture types (cont.)
• Avulsionbone fragments pulled away from
  underlying bone surface or bone totally torn from
  body part
• Linearfracture line parallel to the bones long
  axis
• Transversefracture line at right angle to long
  axis of bone
• Obliquefracture line slanted or diagonal to
  longitudinal axis
• Spiralfracture line spirals around long axis
• Hairlinecommon in skullfracture components
  small and aligned if fracture is pushed
  downward, called a depressed fracture

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Mechanisms of DiseaseBone Fractures

• Fracture types (cont.)
• Greenstickbone bent but broken only on one side
  (common in children)
• Pottsfracture of lower tibia
• Collesfracture of distal radius
• LeFortfracture of face and/or base of skull
• Hangmansfracture of posterior elements in upper
  cervical spine, especially the axis
• Blowoutfracture of the eye orbit

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Mechanisms of DiseaseBone Fractures

• Osgood-Schlatter disease
• Avulsion fracture of tibial tuberosity fragments
  the surface
• Caused by powerful contraction of quadriceps
  muscle group pulling on patellar ligament
  attached to tibial tuberosity
• Common in adolescent athletes in whom patellar
  ligament is stronger than underlying bone

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Mechanisms of DiseaseTreatment of Fractures

• Clinical signs of fracture include pain, loss of
  function, false motion, soft tissue edema,
  deformity, and crepitus
• Initial treatment is realignment and
  immobilization of bone fragments
• Closed reductionalignment completed without
  surgery
• Open reductionsurgery required to align and
  internally immobilize bone fragments with screws,
  wires, plates, or other orthopedic devices
• After reduction, immobilization generally
  accomplished by casts, splints, and bandages
• Traction sometimes usedespecially in children
• Restoration of function is treatment priority
  following healing

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Mechanisms of DiseaseMastoiditis

• Inflammation of air spaces within mastoid portion
  of temporal bone
• Pus may enter mastoid air spaces from middle ear
  infection or otitis media
• Mastoid air cells do not drain into nose as do
  paranasal sinuses
• Infectious material may erode thin, bony
  partition separating air cells from cranial
  cavity, causing intracranial infection
• Treatment is antibiotic therapy and surgical
  incision of eardrum to drain pus from middle ear
• Surgical removal of part of mastoid process of
  temporal bonemastoidectomyis rare

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Mechanisms of DiseaseAbnormal Spinal Curvatures

• Normal curvature of spine is convex through the
  cervical and lumbar regions
• Normal curves give spine strength for support of
  body and balance required to stand and walk
• Abnormal curvatures
• Lordosisabnormally accentuated lumbar curve
  (swayback)
• Frequently seen during pregnancy
• May be secondary to traumatic injury

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Mechanisms of DiseaseAbnormal Spinal Curvatures

• Abnormal curvatures (cont.)
• Kyphosisabnormally accentuated thoracic
  curvature (hunchback)
• Frequent consequence of vertebral compression
  fractures in osteoporosis
• Sign of Scheuermanns disease, which may develop
  in children at puberty

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Mechanisms of DiseaseAbnormal Spinal Curvatures

• Abnormal curvatures (cont.)
• Scoliosisabnormal side-to-side spinal curvature
• Often appears before adolescence
• Treatments vary with severity of curvature
• Milwaukee brace
• Transcutaneous stimulation
• Surgical grafting to the deformed vertebrae of
  bone from elsewhere in skeleton or of metal rods