Chapter 8
Chapter 8
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
Divisions of Skeleton (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
Axial Skeleton
Skull—made up of 28 bones in two major divisions: cranial bones and facial bones (Figures 8-2 to 8-7;
Table 8-3)
Cranial bones
Frontal bone (Figure 8-8, 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
Parietal bones (Figure 8-8, A)
Form the bulging top of the cranium
Form several sutures: lambdoidal suture with occipital bone; squamous suture with temporal bone and part of sphenoid; and coronal suture with frontal bone
Temporal bones (Figure 8-8, B)
Form the lower sides of the cranium and part
of the cranial floor
Contain the inner and middle ears
Occipital bone (Figure 8-8, 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
Frontal bone
Forehead bone
Forms most of the roof of the orbits (eye sockets) and anterior part of the cranial floor
Axial Skeleton
Cranial bones (cont.)
Sphenoid bone (Figure 8-8, 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 8-7)
Contains the sphenoid sinuses
Ethmoid bone (Figure 8-8, F)
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
Facial bones (Table 8-4)
Maxilla (upper jaw) (Figure 8-8, H)
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
Mandible (lower jaw) (Figure 8-8, M)
Largest, strongest bone of the face
Forms the only movable joint of the skull with the temporal bone
Zygomatic bone (Figure 8-8, I)
Shapes the cheek and forms the outer margin of the orbit
Forms the zygomatic arch with the zygomatic process of the temporal bones
Nasal bone (Figures 8-8, L, and 8-10)
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
Lacrimal bone (Figure 8-8, 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 groove for the nasolacrimal (tear) duct
Articulates with the maxilla and the frontal
and ethmoid bones
Axial Skeleton
Facial bones (cont.)
Palatine bone (Figure 8-8, 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
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 (Figure 8-8, G)
Forms posterior portion of the nasal septum
Articulates with the sphenoid, ethmoid, and palatine
bones and maxillae
Eye orbits (Figure 8-7)
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 cranial and nasal cavities and paranasal sinuses
Traumatic injuries may result in “blowout fractures” (Figure 8-7, C)
“Raccoon eyes”—clinical sign of blowout fracture
(Figure 8-7, D)
Fetal skull (Figure 8-11)
Characterized by unique anatomic features not seen in adult skull
Fontanels (unossified areas) or “soft spots” (4) allow skull to “mold” during birth process and permit rapid growth of brain (Table 8-5)
Permits differential growth or appearance of skull components over time
Face—smaller proportion of total cranium at birth (1/8) than in adult (1/2)
Head at birth is ¼ total body height; at maturity is about 1/8 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
Hyoid bone (Figure 8-12)
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
Axial Skeleton
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:
Cervical vertebrae, 7
Thoracic vertebrae, 12
Lumbar vertebrae, 5
Sacrum—in adult, results from fusion of five separate vertebrae
Coccyx—in adult, results from fusion of four or five separate vertebrae
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 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
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
Convexity persists in the thoracic and sacral regions
Concavity persists in the cervical and lumbar regions
C-Spine
First or upper seven
Foramen in each transverse process for transmission of vertebral artery, vein and plexus of nerves.
Short bifurcated spinous processes except on first and seventh vertebra.
Small bodies with large, triangular spinal foramina.
Atlas (C1)
Lacks a body and spinous process
Superior articulating processes are concave ovals that act like rocker-like cradle for the condyles of the occipital bone.
Named atlas because it supports the head.
Allows up and down movement of the head.
Axis (C2)
Second cervical vertebra
Allows rotation movement of head
Has dens, or odontoid process which is a peg or tooth-like projection upward from the body of the axis that allows for side to side rotation of the head.
Axial Skeleton
Vertebral column (cont.)
T-Spine
Next 12 vertebrae
12 pair of ribs attach to these vertebrae
Stronger, with more massive bodies than C-spine
Contain no transverse foramina
Two sets of facets for articulation with ribs
Elongated spinous processes
Lumbar spine
Five vertebrae
Strong, massive, superior articulating processes directed medially instead of upward
Inferior articulating processes , laterally instead of upward
Short blunt spinous process with large amount of muscle attachment
Sternum (Figure 8-15)
Dagger-shaped bone in the middle of the anterior chest wall made up of three parts:
Manubrium—the upper, handle part
Body—the middle, blade part
Xiphoid process—the blunt cartilaginous lower tip, which 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 means of the costal cartilage
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
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
Appendicular Skeleton
Upper extremity (Table 8-7)
Consists of the bones of the shoulder girdle, upper arm, lower arm, wrist, and hand
Shoulder girdle (Figure 8-17)
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
Humerus (Figures 8-18 and 8-19)
The long bone of the upper arm
Articulates proximally with the glenoid fossa of the scapula and distally with the radius and ulna
Ulna
Long bone found on little finger side of forearm
Articulates proximally with humerus and radius and distally with a fibrocartilaginous disk
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
Carpal bones (Figure 8-20)
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
Metacarpal bones
Form framework of hand
Thumb metacarpal forms the most freely movable joint with the carpals
Heads of metacarpals (knuckles) articulate with phalanges
Appendicular Skeleton
Lower extremity
Consists of the bones of hip, thigh, lower leg, ankle, and foot (Table 8-8)
Pelvic girdle is made up 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 made up of three bones that fuse together (Figure 8-22):
Ilium—largest and uppermost
Ischium—strongest and lowermost
Pubis—anteriormost
Femur—longest and heaviest bone in the body (Figure 8-23)
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 the talus
Fibula
The smaller, more laterally and deeply placed
of two leg bones
Articulates with tibia
Foot (Figures 8-24 and 8-25)
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 calcaneus, talus, navicular, cuneiforms, and medial three metatarsals
Lateral longitudinal arch is made up of calcaneus, cuboid, and fourth and fifth metatarsals
Skeletal Differences in Men and Women
Male skeleton is larger and heavier than female skeleton
Pelvic differences (Figure 8-26; Table 8-9)
Male pelvis—deep and funnel-shaped with a narrow pubic arch
Female pelvis—shallow, broad, and flaring with a wider pubic arch
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
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
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
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
The Big Picture
Skeletal system is a good example of increasing structural hierarchy in the body
Skeletal tissues are 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 is more than an assemblage of individual bones—it represents a complex and interdependent functional unit of the body
Mechanisms of Disease—Bone 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)
Displaced, open or compound fractures—do not produce a break in the skin and pose less danger of infection
Nondisplaced, closed or simple fractures—do not produce a break in the skin and pose less danger of infection
Fracture types:
Impacted—one end of fracture driven into diaphysis of other fragment
Complete—break extends across entire section of bone
Incomplete—some fracture components still partially joined
Dentate—fracture components jagged and fit together like teeth on a gear
Comminuted—crushed, small, crumbled bone fragments near fracture
Avulsion—bone fragments pulled away from underlying bone surface or bone totally torn from body part
Linear—fracture line parallel to the bone’s long axis
Transverse—fracture line at right angle to long axis of bone
Oblique—fracture line slanted or diagonal to longitudinal axis
Spiral—fracture line spirals around long axis
Hairline—common in skull—fracture components small and aligned; if fracture is pushed downward, called a depressed fracture
Greenstick—bone bent but broken only on one side (common in children)
Pott’s—fracture of lower tibia
Colles’—fracture of distal radius
LeFort—fracture of face and/or base of skull
Hangman’s—fracture of posterior elements in upper cervical spine, especially the axis
Blowout—fracture of the eye orbit
Mechanisms of Disease—Bone 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
Mechanisms of Disease—Treatment 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 reduction—alignment completed without surgery
Open reduction—surgery 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 used—especially in children
Restoration of function is treatment priority following healing
Mechanisms of Disease—Abnormal 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
Lordosis—abnormally accentuated lumbar curve (“swayback”)
Frequently seen during pregnancy
May be secondary to traumatic injury
Kyphosis—abnormally accentuated thoracic curvature (“hunchback”)
Frequent consequence of vertebral compression fractures in osteoporosis
Sign of Scheuermann’s disease, which may develop
in children at puberty
Scoliosis—abnormal 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
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