Download AXIAL SKELETON (cont.)

Chapter 8: Skeletal System
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INTRODUCTION
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Skeletal tissues form bones—the organs of
the skeletal system
The relations of bones to each other and to
other body structures provide 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
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Figure 8-1; Table 8-1
Axial skeleton: the 80 bones of the head,
neck, and torso; composed of 74 bones that
form the upright axis of the body and six tiny
middle-ear bones
Appendicular skeleton: the 126 bones that
form the appendages to the axial skeleton;
the upper and lower extremities
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AXIAL SKELETON
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Skull: composed of 28 bones in two major
divisions: cranial bones and facial bones
(Figures 8-2 to 8-7; Table 8-3)
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Cranial bones (Figure 8-8)
 Frontal bone
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Parietal bones
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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
Form the bulging top of the cranium
Form several sutures: lambdoid suture with the occipital
bone, squamous suture with the temporal bone and part of
the sphenoid, and coronal suture with the frontal bone
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AXIAL SKELETON (cont.)
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Cranial bones (cont.)
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Temporal bones
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Occipital bone
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Form the lower sides of the cranium and part of the cranial floor
Contain the inner and middle ears
Forms the lower, posterior part of the skull
Forms immovable joints with three other cranial bones and a
movable joint with the first cervical vertebras
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AXIAL SKELETON (cont.)
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Cranial bones (cont.)
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Sphenoid bone
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Ethmoid bone
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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 (Figure 8-7)
Contains the sphenoid sinuses
A complex, irregular bone that lies anterior to the sphenoid
and posterior to the nasal bones
Forms anterior cranial floor, medial orbit walls, upper parts
of the nasal septum, and side walls of the nasal cavity
The cribriform plate is located in the ethmoid
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AXIAL SKELETON (cont.)
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Skull (cont.)
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Facial bones (Table 8-4)
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Maxilla (upper jaw)
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Two maxillae form the keystone of the face
Maxillae articulate with each other and with the nasal, zygomatic,
inferior concha, and palatine bones
Forms parts of the orbital floors, roof of the mouth, and floor and
side walls of the nose
Contains maxillary sinuses
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AXIAL SKELETON (cont.)
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Facial bones (cont.)
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Mandible (lower jaw)
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Zygomatic bone
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Shapes the cheek and forms the outer margin of the orbit
Forms the zygomatic arch with the zygomatic process of the
temporal bones
Nasal bones
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Largest, strongest bone of the face
Forms the only movable joint of the skull with the temporal bone
Both nasal bones form the upper part of the bridge of the nose;
cartilage forms the lower part
Articulate with the ethmoid, nasal septum, frontal bone, maxillae,
and each other
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AXIAL SKELETON (cont.)
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Facial bones (cont.)
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Lacrimal bone
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Palatine bone
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Paper-thin bone that lies just posterior and lateral to each nasal
bone
Forms the nasal cavity and medial wall of the orbit
Contains a groove for the nasolacrimal (tear) duct
Articulates with the maxilla, frontal, and ethmoid bones
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 (cont.)
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Facial bones (cont.)
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Inferior nasal conchae (turbinates)
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Vomer bone
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Form the lower edge projecting into the nasal cavity and form the
nasal meatuses
Articulate with ethmoid, lacrimal, maxillary, and palatine bones
Forms the posterior portion of the nasal septum
Articulates with the sphenoid, ethmoid, palatine, and maxillae
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AXIAL SKELETON (cont.)
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Eye orbits (Figure 8-7)
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Right and left eye orbits
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Contain eyes, associated eye muscles, lacrimal
apparatus, blood vessels, and nerves
Thin and fragile orbital walls separate orbital
structures from the cranial and nasal cavities and
paranasal sinuses
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AXIAL SKELETON (cont.)
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Fetal skull (Figure 8-11)
 Characterized by unique anatomical features not seen in
adult skull
 Four fontanels, or “soft spots,” allow the skull to mold during
the birth process and allow rapid growth of the brain (Table
8-5)
 Permits differential growth or appearance of skull
components over time
 Face: smaller proportion of total cranium at birth (one
eighth) than in adult (one half)
 Head at birth is one fourth the total height; at maturity
about one eighth body height
 Sutures appear with skeletal maturity (Table 8-5)
 Paranasal sinuses: change in size and placement with
skeletal maturity (Figure 8-9)
 Appearance of deciduous and, later, permanent teeth
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AXIAL SKELETON (cont.)
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Hyoid bone (Figure 8-12)
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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
Vertebral column (Figure 8-13)
Forms the flexible longitudinal axis of the skeleton
 Consists of 24 vertebrae plus the sacrum and coccyx
 Segments of the vertebral column:
 Seven cervical vertebrae
 12 thoracic vertebrae
 Five lumbar vertebrae
 Sacrum: in adults, results from the fusion of five
separate vertebrae
 Coccyx: in adults, results from the fusion of four or five
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separate vertebrae
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AXIAL SKELETON (cont.)
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Vertebral column (cont.)
 Characteristics of the vertebrae (Figure 8-14; Table 8-6)
 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 a vertebral
foramen
 Second cervical vertebra has an upward projection,
the dens, to allow rotation of the head
 Seventh cervical vertebra has a long, blunt spinous
process
 Each thoracic vertebra has articular facets for the ribs
 Vertebral column as a whole articulated 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 (cont.)
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Sternum (Figure 8-15)
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Dagger-shaped bone in the middle of the anterior chest
wall made of three parts:
 Manubrium: the upper handle part
 Body: middle blade part
 Xiphoid process: blunt cartilaginous lower tip that ossifies
during adult life
Manubrium articulates with the clavicle and first rib
Next nine ribs join the body of the sternum, either directly
or indirectly, by the costal cartilages
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AXIAL SKELETON (cont.)
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Ribs (Figures 8-15 and 8-16)
 12 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
 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
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Upper extremity (Table 8-7)
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Consists of the bones of the shoulder girdle, upper and
lower parts of the arm, wrist, and hand
Shoulder girdle (Figure 8-17)
 Composed of the scapula and clavicle
 Clavicle forms the only bony joint with the trunk, the
sternoclavicular joint
 At its distal end, the clavicle articulates with the acromion
process of the scapula
Humerus (Figures 8-18 and 8-19)
 The long bone of the upper part of the arm
 Articulates proximally with the glenoid fossa of the scapula
and distally with the radius and ulna
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APPENDICULAR SKELETON
(cont.)
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Upper extremity (cont.)
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Ulna
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Radius
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The long bone found on the little finger side of the
forearm
Articulates proximally with the humerus and radius
and distally with a fibrocartilaginous disk
The long bone found on the thumb side of the forearm
Articulates proximally with the capitulum of the
humerus and the radial notch of the ulna; articulates
distally with the scaphoid and lunate carpals and with
the head of the ulna
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APPENDICULAR SKELETON
(cont.)
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Upper extremity (cont.)
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Carpal bones (Figure 8-20)
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Eight small bones that form the wrist
Carpals are bound closely and firmly by ligaments and
form two rows of four carpals each
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Proximal row is composed of the pisiform, triquetrum, lunate, and
scaphoid
Distal row is composed of the hamate, capitate, trapezoid, and
trapezium
The joints between the radius and carpals allow wrist
and hand movements
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APPENDICULAR SKELETON
(cont.)
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Upper extremity (cont.)
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Metacarpal bones
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Form the framework of the hand
The thumb metacarpal forms the most freely movable
joint with the carpals
Heads of the metacarpals (the knuckles) articulate
with the phalanges
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APPENDICULAR SKELETON
(cont.)
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Lower extremity
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Consists of the bones of the hip, thigh, lower part of the
leg, ankle, and foot (Table 8-8)
Pelvic girdle is composed of the sacrum and the two coxal
bones bound tightly by strong ligaments (Figure 8-21)
 A stable circular base that supports the trunk and attaches
the lower extremities to it
 Each coxal bone is composed of three bones that fuse
together (Figure 8-22):
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Ilium: largest and uppermost
Ischium: strongest and lowermost
Pubis: anteriormost
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APPENDICULAR SKELETON
(cont.)
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Lower extremity (cont.)
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Femur: longest and heaviest bone in the body (Figure 823)
Patella: largest 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 talus
Fibula
 The smaller, more laterally and deeply placed of the two leg
bones
 Articulates with the tibia
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APPENDICULAR SKELETON
(cont.)
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Lower extremity (cont.)
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Foot (Figures 8-24 and 8-25)
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Structure is similar to that of the hand with adaptations
for supporting weight
Foot bones are held together to form spring arches
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Medial longitudinal arch is composed of the calcaneus, talus,
navicular, cuneiforms, and medial three metatarsals
Lateral longitudinal arch is composed of the calcaneus, cuboid,
and fourth and fifth metatarsals
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SKELETAL DIFFERENCES IN
MEN AND WOMEN
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Male skeleton is larger and heavier than
female skeleton
Pelvic differences (Figure 8-26; Table 8-9)
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Male pelvis: deep and funnel shaped with a
narrow pubic arch
Female pelvis: shallow, broad, and flaring with a
wider pubic arch
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THE BIG PICTURE: SKELETAL
SYSTEM
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Skeletal system is a good example of increasing
structural hierarchy in the body
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Skeletal tissues grouped into discrete organs: bones
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 more than an assemblage of individual
bones; it represents a complex and interdependent
functional unit of the body
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