1. Chapter 9: Skeletal System
Anatomy & Physiology
Chapter 9: Skeletal System

2. Introduction
Skeletal tissues form bones—the 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 2

3. Divisions of the Skeleton (Figure 9-1; Table 9-1)
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 3

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5. Axial Skeleton
Skull—made up of 28 bones in two major divisions: cranial bones and facial bones (Figures 9-2 to 9-7; Table 9-3)
Cranial bones
Frontal bone (Figure 9-8, C)
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 5

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16. Axial Skeleton Cranial bones (cont) Parietal bones (Figure 9-8, A)
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 16

17. Axial Skeleton Cranial bones (cont) Temporal bones (Figure 9-8, B)
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
Occipital bone (Figure 9-8, D)
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 17

18. Axial Skeleton Cranial bones (cont) Sphenoid bone (Figure 9-8, E)
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 9-7)
Contains the sphenoid sinuses 18

19. Axial Skeleton Cranial bones (cont) Ethmoid bone (Figure 9-8, F)
A complex, 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 19

20. Axial Skeleton Skull (cont) Facial bones (Table 9-4)
Maxilla (upper jaw) (Figure 9-8, H)
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 sidewalls of the nose
Contains maxillary sinuses 20

21. Axial Skeleton Facial bones (cont)
Mandible (lower jaw) (Figure 9-8, M)
Largest, strongest bone of the face
Forms the only movable joint of the skull with the temporal bone
Zygomatic bone (Figure 9-8, I)
Shapes the cheek and forms the outer margin of the orbit
Forms the zygomatic arch with the zygomatic process of the temporal bones 21

22. Axial Skeleton Facial bones (cont)
Nasal bone (Figures 9-8, L and 9-10)
Both nasal bones form the upper part of the bridge of the nose, whereas cartilage forms the lower part
Articulates with the ethmoid, nasal septum, frontal bone, maxillae, and the other nasal bone 22

23. Axial Skeleton Facial bones (cont) Lacrimal bone (Figure 9-8, K)
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 23

24. Axial Skeleton Facial bones (cont) Palatine bone (Figure 9-8, J)
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 24

25. Axial Skeleton Facial bones (cont) Inferior nasal conchae (turbinates)
Form the lower edge projecting into the nasal cavity and form the nasal meatus
Articulate with ethmoid, lacrimal, maxillary, and palatine bones
Vomer bone (Figure 9-8, G)
Forms the posterior portion of the nasal septum
Articulates with the sphenoid, ethmoid, palatine, and maxillae 25

26. Axial Skeleton Eye orbits (Figure 9-7) Right and left eye orbits
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 26

27. Axial Skeleton Fetal skull (Figure 9-11)
Characterized by unique anatomical features not seen in adult skull
Fontanels or “soft spots” (4) allow the skull to “mold” during the birth process and also allow for rapid growth of the brain (Table 9-5) 27

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29. Axial Skeleton Fetal skull (cont)
Permits differential growth or appearance of skull components over time
Face—smaller proportion of total cranium at birth {1/8} than in adult {½}
Head at birth is {¼} the total height; at maturity about {1/8} body height
Sutures appear with skeletal maturity (Table 9-5)
Paranasal sinuses—change in size and placement with skeletal maturity (Figure 9-9)
Appearance of deciduous and, later, permanent teeth 29

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31. Axial Skeleton Hyoid bone (Figure 9-12)
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 31

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33. Axial Skeleton Vertebral column (Figure 9-13)
Forms the flexible longitudinal axis of the skeleton
Consists of 24 vertebrae plus the sacrum and coccyx 33

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35. Axial Skeleton Vertebral column (cont)
Characteristics of the vertebrae (Figure 9-14; Table 9-6)
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 vertebrae 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 35

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39. Axial Skeleton Vertebral column (cont)
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 39

40. Axial Skeleton Sternum (Figure 9-15)
Dagger-shaped bone in the middle of the anterior chest wall made up of three parts:
Manubrium—the upper handle part
Body—middle blade part
Xiphoid process—blunt cartilaginous lower tip, which ossifies during adult life 40

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42. 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 cartilages 42

43. Axial Skeleton Ribs (Figures 9-15 and 9-16)
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
From its vertebral attachment, each rib curves outward, then forward and downward 43

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45. Axial Skeleton Ribs (cont) 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 45

46. Appendicular Skeleton
Upper extremity (Table 9-7)
Consists of the bones of the shoulder girdle, upper and lower parts of the arm, wrist, and hand
Shoulder girdle (Figure 9-17)
Made up 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 46

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48. Appendicular Skeleton
Upper extremity (cont)
Humerus (Figures 9-18 and 9-19)
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
Ulna
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 48

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51. Appendicular Skeleton
Upper extremity (cont)
Carpal bones (Figure 9-20)
Eight small bones that form the wrist
Carpal bones are bound closely and firmly by ligaments and form two rows of four carpals each
Proximal row is made up of the pisiform, triquetrum, lunate, and scaphoid
Distal row is made up of the hamate, capitate, trapezoid, and trapezium
The joints between the radius and carpal bones allow wrist and hand movements 51

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53. Appendicular Skeleton
Upper extremity (cont)
Metacarpal bones
Form the framework of the hand
The thumb metacarpal forms the most freely movable joint with the carpal bones
Heads of the metacarpal bones (the knuckles) articulate with the phalanges 53

54. Appendicular Skeleton
Lower extremity
Consists of the bones of the hip, thigh, leg, ankle, and foot (Table 9-8)
Pelvic girdle is made up of the sacrum and the two coxal bones bound tightly by strong ligaments (Figure 9-21)
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 (Figure 9-22):
Ilium—largest and uppermost
Ischium—strongest and lowermost
Pubis—anterior most 54

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57. Appendicular Skeleton
Lower extremity (cont)
Femur—longest and heaviest bone in the body (Figure 9-23)
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 57

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59. Appendicular Skeleton
Lower extremity (cont)
Fibula
The smaller, more laterally and deeply placed of the two leg bones
Articulates with the tibia 59

60. Appendicular Skeleton
Lower extremity (cont)
Foot (Figures 9-24 and 9-25)
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 the calcaneus, talus, navicular, cuneiforms, and medial three metatarsal bones
Lateral longitudinal arch is made up of the calcaneus, cuboid, and fourth and fifth metatarsal bones 60

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63. Skeletal Differences Between Men and Women
Male skeleton is larger and heavier than female skeleton
Pelvic differences (Figure 9-26; Table 9-9)
Male pelvis—deep and funnel-shaped with a narrow pubic arch
Female pelvis—shallow, broad, and flaring with a wider pubic arch 63

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65. Cycle of Life: The Skeletal System
Changes in the skeleton begin at fertilization and continue over a lifetime; changes can be positive or negative
Incompletely ossified skeleton in children provides the resiliency needed to withstand stress without breaking easily
Dense bone structure in young and middle adulthood permits bearing heavy loads 65

66. Cycle of Life: The Skeletal System
In later adulthood, reduced bone density makes fractures more likely and causes changes in posture and overall height
Details of aging effects are found in Mechanisms of Disease section 66

67. The Big Picture: Skeletal System
Skeletal system is a good example of increasing structural hierarchy in the body
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 a collection of individual bones—it represents a complex and interdependent functional unit of the body 67