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

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

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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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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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

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

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

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

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

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

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

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

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

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

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

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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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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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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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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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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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

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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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

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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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

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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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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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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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

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

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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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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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

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

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