The Skeletal System PDF

06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 105 Copyright © 2007 by F. A. Davis. The Skeletal System New Terminology Related Clinical Terminology Appendicular (AP-en-DIK-yoo-lar)...

06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 105 Copyright © 2007 by F. A. Davis. The Skeletal System New Terminology Related Clinical Terminology Appendicular (AP-en-DIK-yoo-lar) Autoimmune disease Articulation (ar-TIK-yoo-LAY-shun) (AW-toh-im-YOON di-ZEEZ) Axial (AK-see-uhl) Bursitis (burr-SIGH-tiss) Bursa (BURR-sah) Cleft palate (KLEFT PAL-uht) Diaphysis (dye-AFF-i-sis) Fracture (FRAK-chur) Epiphyseal disc (e-PIFF-i-SEE-al DISK) Herniated disc (HER-nee-ay-ted DISK) Epiphysis (e-PIFF-i-sis) Kyphosis (kye-FOH-sis) Fontanel (FON-tah-NELL) Lordosis (lor-DOH-sis) Haversian system (ha-VER-zhun SIS-tem) Osteoarthritis (AHS-tee-oh-ar-THRY-tiss) Ligament (LIG-uh-ment) Osteomyelitis (AHS-tee-oh-my-uh-LYE-tiss) Ossification (AHS-i-fi-KAY-shun) Osteoporosis (AHS-tee-oh-por-OH-sis) Osteoblast (AHS-tee-oh-BLAST) Rheumatoid arthritis Osteoclast (AHS-tee-oh-KLAST) (ROO-muh-toyd ar-THRY-tiss) Paranasal sinus (PAR-uh-NAY-zuhl SIGH-nus) Rickets (RIK-ets) Periosteum (PER-ee-AHS-tee-um) Scoliosis (SKOH-lee-OH-sis) Suture (SOO-cher) Symphysis (SIM-fi-sis) Synovial fluid (sin-OH-vee-al FLOO-id) Terms that appear in bold type in the chapter text are defined in the glossary, which begins on page 547. 105 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 106 Copyright © 2007 by F. A. Davis. 106 The Skeletal System I magine for a moment that people did not have skeletons. What comes to mind? Probably that each of late the amount of calcium that is deposited in, or removed from, the bone matrix. us would be a little heap on the floor, much like a jel- In bone as an organ, two types of bone tissue are lyfish out of water. Such an image is accurate and present (Fig. 6–1). Compact bone looks solid but is reflects the most obvious function of the skeleton: to very precisely structured. Compact bone is made of support the body. Although it is a framework for the osteons or haversian systems, microscopic cylinders body, the skeleton is not at all like the wooden beams of bone matrix with osteocytes in concentric rings that support a house. Bones are living organs that around central haversian canals. In the haversian actively contribute to the maintenance of the internal canals are blood vessels; the osteocytes are in contact environment of the body. with these blood vessels and with one another through The skeletal system consists of bones and other microscopic channels (canaliculi) in the matrix. structures that make up the joints of the skeleton. The The second type of bone tissue is spongy bone, types of tissue present are bone tissue, cartilage, and which does look rather like a sponge with its visible fibrous connective tissue, which forms the ligaments holes or cavities. Osteocytes, matrix, and blood vessels that connect bone to bone. are present but are not arranged in haversian systems. The cavities in spongy bone often contain red bone marrow, which produces red blood cells, platelets, FUNCTIONS OF THE SKELETON and the five kinds of white blood cells. 1. Provides a framework that supports the body; the muscles that are attached to bones move the skele- CLASSIFICATION OF BONES ton. 2. Protects some internal organs from mechanical 1. Long bones—the bones of the arms, legs, hands, injury; the rib cage protects the heart and lungs, for and feet (but not the wrists and ankles). The shaft example. of a long bone is the diaphysis, and the ends are 3. Contains and protects the red bone marrow, the called epiphyses (see Fig. 6–1). The diaphysis is primary hemopoietic (blood-forming) tissue. made of compact bone and is hollow, forming a 4. Provides a storage site for excess calcium. Calcium canal within the shaft. This marrow canal (or may be removed from bone to maintain a normal medullary cavity) contains yellow bone marrow, blood calcium level, which is essential for blood which is mostly adipose tissue. The epiphyses are clotting and proper functioning of muscles and made of spongy bone covered with a thin layer of nerves. compact bone. Although red bone marrow is pres- ent in the epiphyses of children’s bones, it is largely replaced by yellow bone marrow in adult bones. TYPES OF BONE TISSUE 2. Short bones—the bones of the wrists and ankles. 3. Flat bones—the ribs, shoulder blades, hip bones, Bone was described as a tissue in Chapter 4. Recall and cranial bones. that bone cells are called osteocytes, and the matrix 4. Irregular bones—the vertebrae and facial bones. of bone is made of calcium salts and collagen. The calcium salts are calcium carbonate (CaCO3) and cal- Short, flat, and irregular bones are all made of cium phosphate (Ca3(PO4)2), which give bone the spongy bone covered with a thin layer of compact strength required to perform its supportive and pro- bone. Red bone marrow is found within the spongy tective functions. Bone matrix is non-living, but it bone. changes constantly, with calcium that is taken from The joint surfaces of bones are covered with artic- bone into the blood replaced by calcium from the diet. ular cartilage, which provides a smooth surface. Cov- In normal circumstances, the amount of calcium that ering the rest of the bone is the periosteum, a fibrous is removed is replaced by an equal amount of calcium connective tissue membrane whose collagen fibers deposited. This is the function of osteocytes, to regu- merge with those of the tendons and ligaments that 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 107 Copyright © 2007 by F. A. Davis. Proximal epiphysis Osteon Haversian canal (haversian system) Concentric rings of osteocytes Marrow Diaphysis Yellow bone marrow Marrow (medullary) cavity Periosteum Distal epiphysis Venule Compact bone Arteriole Spongy bone Canaliculi Fibrous layer Periosteum Osteocyte Osteogenic layer (osteoblasts) A B Figure 6–1. Bone tissue. (A) Femur with distal end cut in longitudinal section. (B) Compact bone showing haversian systems (osteons). QUESTION: What is the purpose of the blood vessels in bone tissue? 107 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 108 Copyright © 2007 by F. A. Davis. 108 The Skeletal System are attached to the bone. The periosteum anchors junction of the diaphysis with each epiphysis. An epi- these structures and contains both the blood vessels physeal disc is still cartilage, and the bone grows in that enter the bone itself and osteoblasts that will length as more cartilage is produced on the epiphysis become active if the bone is damaged. side (see Fig. 6–3). On the diaphysis side, osteoblasts produce bone matrix to replace the cartilage. Between the ages of 16 and 25 years (influenced by estrogen or EMBRYONIC GROWTH OF BONE testosterone), all of the cartilage of the epiphyseal discs is replaced by bone. This is called closure of the During embryonic development, the skeleton is first epiphyseal discs (or we say the discs are closed), and made of cartilage and fibrous connective tissue, which the bone lengthening process stops. are gradually replaced by bone. Bone matrix is pro- Also in bones are specialized cells called osteo- duced by cells called osteoblasts (a blast cell is a “grow- clasts (a clast cell is a “destroying” cell), which are able ing” or “producing” cell, and osteo means “bone”). In to dissolve and reabsorb the minerals of bone matrix, the embryonic model of the skeleton, osteoblasts dif- a process called resorption. Osteoclasts are very ferentiate from the fibroblasts that are present. The active in embryonic long bones, and they reabsorb production of bone matrix, called ossification, begins bone matrix in the center of the diaphysis to form the in a center of ossification in each bone. marrow canal. Blood vessels grow into the marrow The cranial and facial bones are first made of canals of embryonic long bones, and red bone marrow fibrous connective tissue. In the third month of fetal is established. After birth, the red bone marrow is development, fibroblasts (spindle-shaped connective replaced by yellow bone marrow. Red bone marrow tissue cells) become more specialized and differentiate remains in the spongy bone of short, flat, and irregu- into osteoblasts, which produce bone matrix. From lar bones. For other functions of osteoclasts and each center of ossification, bone growth radiates out- osteoblasts, see Box 6–1: Fractures and Their Repair. ward as calcium salts are deposited in the collagen of the model of the bone. This process is not complete at birth; a baby has areas of fibrous connective tissue FACTORS THAT AFFECT BONE remaining between the bones of the skull. These GROWTH AND MAINTENANCE are called fontanels (Fig. 6–2), which permit com- pression of the baby’s head during birth without 1. Heredity—each person has a genetic potential for breaking the still thin cranial bones. The fontanels height, that is, a maximum height, with genes also permit the growth of the brain after birth. You inherited from both parents. Many genes are may have heard fontanels referred to as “soft spots,” involved, and their interactions are not well under- and indeed they are. A baby’s skull is quite fragile and stood. Some of these genes are probably those for must be protected from trauma. By the age of 2 years, the enzymes involved in cartilage and bone pro- all the fontanels have become ossified, and the skull duction, for this is how bones grow. becomes a more effective protective covering for the 2. Nutrition—nutrients are the raw materials of brain. which bones are made. Calcium, phosphorus, and The rest of the embryonic skeleton is first made of protein become part of the bone matrix itself. cartilage, and ossification begins in the third month of Vitamin D is needed for the efficient absorption of gestation in the long bones. Osteoblasts produce bone calcium and phosphorus by the small intestine. matrix in the center of the diaphyses of the long bones Vitamins A and C do not become part of bone but and in the center of short, flat, and irregular bones. are necessary for the process of bone matrix forma- Bone matrix gradually replaces the original cartilage tion (ossification). Without these and other nutri- (Fig. 6–3). ents, bones cannot grow properly. Children who The long bones also develop centers of ossification are malnourished grow very slowly and may not in their epiphyses. At birth, ossification is not yet com- reach their genetic potential for height. plete and continues throughout childhood. In long 3. Hormones—endocrine glands produce hormones bones, growth occurs in the epiphyseal discs at the that stimulate specific effects in certain cells. (text continued on page 112) 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 109 Copyright © 2007 by F. A. Davis. Anterior fontanel Parietal bone Parietal bone Frontal bone Posterior fontanel Posterior fontanel Frontal bone Occipital bone Mastoid fontanel Occipital bone Temporal bone Anterior fontanel Sphenoid fontanel Mandible Sphenoid bone Zygomatic bone Maxilla A B C D Figure 6–2. Infant skull with fontanels. (A) Lateral view of left side. (B) Superior view. (C) Fetal skull in anterior superior view. (D) Fetal skull in left lateral view. Try to name the bones; use part A as a guide. The fontanels are translucent connective tissue. (C and D pho- tographs by Dan Kaufman.) QUESTION: What is the difference between the frontal bone of the infant skull and that of the adult skull? 109 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 110 Copyright © 2007 by F. A. Davis. Chondrocytes producing cartilage B Epiphyseal disc Osteoblasts producing bone Bone Epiphyseal disc Cartilage Medullary cavity containing marrow Compact bone Secondary ossification Cartilaginous center model Bone collar Compact bone and calcifying cartilage in ossification center Medullary cavity and development A of secondary ossification centers Spongy bone Articular cartilage Figure 6–3. The ossification process in a long bone. (A) Progression of ossification from the cartilage model of the embryo to the bone of a young adult. (B) Microscopic view of an epiphyseal disc showing cartilage production and bone replacement. QUESTION: The epiphyseal discs of the bone on the far right are closed. What does that mean? 110 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 111 Copyright © 2007 by F. A. Davis. BOX 6–1 FRACTURES AND THEIR REPAIR A fracture means that a bone has been broken. nutrition. The elderly and those in poor health often There are different types of fractures classified as to have slow healing of fractures. A diet with sufficient extent of damage. calcium, phosphorus, vitamin D, and protein is also Simple (closed)—the broken parts are still in nor- important. If any of these nutrients is lacking, bone mal anatomic position; surrounding tissue damage repair will be a slower process. is minimal (skin is not pierced). Compound (open)—the broken end of a bone has been moved, and it pierces the skin; there may be extensive damage to surrounding blood vessels, nerves, and muscles. Greenstick—the bone splits longitudinally. The bones of children contain more collagen than do adult bones and tend to splinter rather than break completely. Comminuted—two or more intersecting breaks create several bone fragments. Impacted—the broken ends of a bone are forced into one another; many bone fragments may be created. Pathologic (spontaneous)—a bone breaks with- out apparent trauma; may accompany bone disor- ders such as osteoporosis. The Repair Process Even a simple fracture involves significant bone damage that must be repaired if the bone is to resume its normal function. Fragments of dead or damaged bone must first be removed. This is accomplished by osteoclasts, which dissolve and reabsorb the calcium salts of bone matrix. Imagine a building that has just collapsed; the rubble must be removed before reconstruction can take place. This is what the osteoclasts do. Then, new bone must be produced. The inner layer of the perios- teum contains osteoblasts that are activated when bone is damaged. The osteoblasts produce bone matrix to knit the broken ends of the bone together. Because most bone has a good blood supply, the repair process is usually relatively rapid, and a sim- ple fracture often heals within 6 weeks. Some parts of bones, however, have a poor blood supply, and repair of fractures takes longer. These areas are the neck of the femur (the site of a “fractured hip”) and the lower third of the tibia. Box Figure 6–A Types of fractures. Several types of Other factors that influence repair include the fractures are depicted in the right arm. age of the person, general state of health, and 111 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 112 Copyright © 2007 by F. A. Davis. 112 The Skeletal System Several hormones make important contributions to strong cords or sheets of fibrous connective tissue. The bone growth and maintenance. These include importance of ligaments becomes readily apparent growth hormone, thyroxine, parathyroid hormone, when a joint is sprained. A sprain is the stretching or and insulin, which help regulate cell division, pro- even tearing of the ligaments of a joint, and though the tein synthesis, calcium metabolism, and energy bones are not broken, the joint is weak and unsteady. production. The sex hormones estrogen or testos- We do not often think of our ligaments, but they are terone help bring about the cessation of bone necessary to keep our bones in the proper positions to growth. The hormones and their specific functions keep us upright or to bear weight. are listed in Table 6–1. There are 206 bones in total, and the complete 4. Exercise or “stress”—for bones, exercise means skeleton is shown in Fig. 6–4. bearing weight, which is just what bones are spe- cialized to do. Without this stress (which is nor- SKULL mal), bones will lose calcium faster than it is replaced. Exercise need not be strenuous; it can be The skull consists of 8 cranial bones and 14 facial as simple as the walking involved in everyday activ- bones. Also in the head are three small bones in each ities. Bones that do not get this exercise, such as middle ear cavity and the hyoid bone that supports the those of patients confined to bed, will become thin- base of the tongue. The cranial bones form the brain- ner and more fragile. This condition is discussed case (lined with the meninges) that encloses and pro- further in Box 6–2: Osteoporosis. tects the brain, eyes, and ears. The names of some of these bones will be familiar to you; they are the same as the terminology used (see Chapter 1) to describe THE SKELETON areas of the head. These are the frontal bone, parietal bones (two), temporal bones (two), and occipital bone. The human skeleton has two divisions: the axial skele- The sphenoid bone and ethmoid bone are part of the ton, which forms the axis of the body, and the appen- floor of the braincase and the orbits (sockets) for dicular skeleton, which supports the appendages or the eyes. The frontal bone forms the forehead and limbs. The axial skeleton consists of the skull, vertebral the anterior part of the top of the skull. Parietal means column, and rib cage. The bones of the arms and “wall,” and the two large parietal bones form the pos- legs and the shoulder and pelvic girdles make up the terior top and much of the side walls of the skull. Each appendicular skeleton. Many bones are connected to temporal bone on the side of the skull contains an other bones across joints by ligaments, which are external auditory meatus (ear canal), a middle ear cav- Table 6–1 HORMONES INVOLVED IN BONE GROWTH AND MAINTENANCE Growth hormone (anterior pituitary gland) Increases the rate of mitosis of chondrocytes and osteoblasts Increases the rate of protein synthesis (collagen, cartilage matrix, and enzymes for cartilage and bone formation) Thyroxine (thyroid gland) Increases the rate of protein synthesis Increases energy production from all food types Insulin (pancreas) Increases energy production from glucose Parathyroid hormone (parathyroid glands) Increases the reabsorption of calcium from bones to the blood (raises blood calcium level) Increases the absorption of calcium by the small intestine and kid- neys (to the blood) Calcitonin (thyroid gland) Decreases the reabsorption of calcium from bones (lowers blood calcium level) Estrogen (ovaries) or Promotes closure of the epiphyses of long bones (growth stops) Testosterone (testes) Helps retain calcium in bones to maintain a strong bone matrix 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 113 Copyright © 2007 by F. A. Davis. The Skeletal System 113 BOX 6–2 OSTEOPOROSIS Bone is an active tissue; calcium is constantly being As bones lose calcium and become thin and brit- removed to maintain normal blood calcium levels. tle, fractures are much more likely to occur. Among Usually, however, calcium is replaced in bones at a elderly women, a fractured hip (the neck of the rate equal to its removal, and the bone matrix femur) is an all-too-common consequence of this remains strong. degenerative bone disorder. Such a serious injury is Osteoporosis is characterized by excessive loss not inevitable, however, and neither is the thinning of calcium from bones without sufficient replace- of the vertebrae that bows the spines of some eld- ment. Research has suggested that a certain gene erly people. After menopause, women may wish to for bone buildup in youth is an important factor; have a bone density test to determine the strength less buildup would mean earlier bone thinning. of their bone matrix. Several medications are avail- Contributing environmental factors include smok- able that diminish the rate of bone loss. A diet high ing, insufficient dietary intake of calcium, inactivity, in calcium and vitamin D is essential for both men and lack of the sex hormones. Osteoporosis is most and women, as is moderate exercise. Young women common among elderly women, because estrogen and teenagers should make sure they get adequate secretion decreases sharply at menopause (in older dietary calcium to form strong bone matrix, men, testosterone is still secreted in significant because this will delay the serious effects of osteo- amounts). Factors such as bed rest or inability to porosis later in life. get even minimal exercise will make calcium loss even more rapid. Normal Bone Osteoporosis A B Box Figure 6–B (A) Normal spongy bone, as in the body of a vertebra. (B) Spongy bone thinned by osteoporosis. ity, and an inner ear labyrinth. The occipital bone bone has a vertical projection called the crista galli forms the lower, posterior part of the braincase. Its (“rooster’s comb”) that anchors the cranial meninges. foramen magnum is a large opening for the spinal The rest of the ethmoid bone forms the roof and cord, and the two condyles (rounded projections) on upper walls of the nasal cavities, and the upper part of either side articulate with the atlas, the first cervical the nasal septum. vertebra. The sphenoid bone is said to be shaped like All of the joints between cranial bones are immov- a bat, and the greater wing is visible on the side of the able joints called sutures. It may seem strange to refer skull between the frontal and temporal bones. The to a joint without movement, but the term joint (or body of the bat has a depression called the sella tur- articulation) is used for any junction of two bones. cica, which encloses the pituitary gland. The ethmoid (The classification of joints will be covered later in 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 114 Copyright © 2007 by F. A. Davis. 114 The Skeletal System Skull (cranium) Zygomatic arch Maxilla Cervical vertebrae Mandible Thoracic vertebrae Clavicle Sternum Scapula Humerus Ribs Lumbar vertebrae Radius Ulna Ilium Carpals Sacrum Figure 6–4. Skeleton. Anterior view. Metacarpals Coccyx QUESTION: Which of the bones Phalanges shown here would be classified Pubis as irregular bones? Ischium Femur Patella Tibia Fibula Tarsals Metatarsals Phalanges this chapter.) In a suture, the serrated, or sawtooth, the lambdoidal suture between the occipital and pari- edges of adjacent bones fit into each other. These etal bones. Not visible is the sagittal suture, where the interlocking projections prevent sliding or shifting of two parietal bones articulate along the midline of the the bones if the skull is subjected to a blow or pres- top of the skull. All the bones of the skull, as well as sure. In Fig. 6–5 you can see the coronal suture the large sutures, are shown in Figs. 6–5 through 6–8. between the frontal and parietal bones, the squamosal Their anatomically important parts are described in suture between the parietal and temporal bones, and Table 6–2. 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 115 Copyright © 2007 by F. A. Davis. Parietal bone Coronal suture Frontal bone Squamosal suture Sphenoid bone Ethmoid bone Lacrimal bone Temporal bone Lacrimal canal Nasal bone Lambdoidal suture Occipital bone Zygomatic bone Zygomatic process Condyloid process Mandibular fossa Mastoid process Maxilla External auditory meatus Mental foramen Occipital bone Coronoid process Mandible Frontal bone Body Zygomatic bone Frontal bone Maxillary bone Coronal suture Parietal bone Mandible Squamosal suture Parietal bone Temporal bone Temporal bone Nasal bone Sphenoid bone Sphenoid bone Perpendicular plate (ethmoid) Ethmoid bone Zygomatic bone Lacrimal bone Middle nasal concha (ethmoid) Vomer Nasal bone Inferior nasal concha Maxilla Inferior nasal concha Mandible Vomer Mental foramen Palatine bone Figure 6–5. Skull. Lateral view of right side. Figure 6–6. Skull. Anterior view. QUESTION: What might be the purpose of the openings at the back of the eye sockets? 115 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 116 Copyright © 2007 by F. A. Davis. 116 The Skeletal System Palatine process (maxilla) Palatine bone Zygomatic bone Vomer Zygomatic process Temporal bone Styloid process External auditory meatus Mastoid process Foramen magnum Occipital condyles Occipital bone Figure 6–7. Skull. Inferior view with mandible removed. QUESTION: What is the purpose of the foramen magnum? Of the 14 facial bones, only the mandible (lower The plow-shaped vomer forms the lower part of the jaw) is movable; it forms a condyloid joint with each nasal septum; it articulates with the ethmoid bone. On temporal bone. The other joints between facial bones either side of the vomer are the conchae, six scroll- are all sutures. The maxillae are the two upper jaw like bones that curl downward from the sides of the bones, which also form the anterior portion of the nasal cavities; they help increase the surface area of the hard palate (roof of the mouth). Sockets for the roots nasal mucosa. These facial bones are included in Table of the teeth are found in the maxillae and the 6–2. mandible. The two nasal bones form the bridge of Paranasal sinuses are air cavities located in the the nose where they articulate with the frontal bone maxillae and frontal, sphenoid, and ethmoid bones (the rest of the nose is supported by cartilage). There (Fig. 6–9). As the name paranasal suggests, they open is a lacrimal bone at the medial side of each orbit; the into the nasal cavities and are lined with ciliated lacrimal canal contains the lacrimal sac, a passageway epithelium continuous with the mucosa of the nasal for tears. Each of the two zygomatic bones forms the cavities. We are aware of our sinuses only when they point of a cheek, and articulates with the maxilla, become “stuffed up,” which means that the mucus frontal bone, and temporal bone. The two palatine they produce cannot drain into the nasal cavities. This bones are the posterior portion of the hard palate. may happen during upper respiratory infections such (text continued on page 119) 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 117 Copyright © 2007 by F. A. Davis. Crista galli Ethmoid bone Cribriform plate Frontal bone Olfactory foramina Sphenoid bone Greater wing Sella turcica Squamosal suture Temporal bone Parietal bone Lambdoidal suture Foramen magnum Occipital bone A C Crista galli B Sella turcica Figure 6–8. (A) Skull. Superior view with the top of cranium removed. (B) Sphenoid bone in superior view. (C) Ethmoid bone in superior view. (B and C photographs by Dan Kaufman.) QUESTION: What are the olfactory foramina of the ethmoid bone for? 117 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 118 Copyright © 2007 by F. A. Davis. Table 6–2 BONES OF THE SKULL—IMPORTANT PARTS Terminology of Bone Markings Foramen—a hole or opening Meatus—a tunnel-like cavity Condyle—a rounded projection Fossa—a depression Process—a projection Plate—a flat projection Crest—a ridge or edge Facet—a flat projection Tubercle—a round projection Bone Part Description Frontal Frontal sinus Air cavity that opens into nasal cavity Coronal suture Joint between frontal and parietal bones Parietal (2) Sagittal suture Joint between the 2 parietal bones Temporal (2) Squamosal suture Joint between temporal and parietal bone External auditory meatus The tunnel-like ear canal Mastoid process Oval projection behind the ear canal Mastoid sinus Air cavity that opens into middle ear Mandibular fossa Oval depression anterior to the ear canal; artic- ulates with mandible Zygomatic process Anterior projection that articulates with the zygomatic bone Occipital Foramen magnum Large opening for the spinal cord Condyles Oval projections on either side of the foramen magnum; articulate with the atlas Lambdoidal suture Joint between occipital and parietal bones Sphenoid Greater wing Flat, lateral portion between the frontal and temporal bones Sella turcica Central depression that encloses the pituitary gland Sphenoid sinus Air cavity that opens into nasal cavity Ethmoid Ethmoid sinus Air cavity that opens into nasal cavity Crista galli Superior projection for attachment of meninges Cribriform plate and On either side of base of crista galli; olfactory olfactory foramina nerves pass through foramina Perpendicular plate Upper part of nasal septum Conchae (4 are part of Shelf-like projections into nasal cavities that ethmoid; 2 inferior are increase surface area of nasal mucosa separate bones) Mandible Body U-shaped portion with lower teeth Condyles Oval projections that articulate with the tem- poral bones Sockets Conical depressions that hold roots of lower teeth Maxilla (2) Maxillary sinus Air cavity that opens into nasal cavity Palatine process Projection that forms anterior part of hard palate Sockets Conical depressions that hold roots of upper teeth Nasal (2) — Form the bridge of the nose Lacrimal (2) Lacrimal canal Opening for nasolacrimal duct to take tears to nasal cavity Zygomatic (2) — Form point of cheek; articulate with frontal, temporal, and maxillae Palatine (2) — Form the posterior part of hard palate Vomer — Lower part of nasal septum 118 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 119 Copyright © 2007 by F. A. Davis. The Skeletal System 119 Ethmoid sinus Frontal sinus Sphenoid sinus Ethmoid sinus Maxillary sinus A B Figure 6–9. Paranasal sinuses. (A) Anterior view of the skull. (B) Left lateral view of skull. QUESTION: Which of these sinuses often cause the pain of a sinus headache? as colds, or with allergies such as hay fever. These of vertebrae indicate their location along the length of sinuses, however, do have functions: They make the the spinal column. There are 7 cervical vertebrae, 12 skull lighter in weight, because air is lighter than bone, thoracic, 5 lumbar, 5 sacral fused into 1 sacrum, and and they provide resonance for the voice, meaning 4 to 5 small coccygeal vertebrae fused into 1 coccyx more air to vibrate and thus deepen the pitch of the (Fig. 6–10). voice. The seven cervical vertebrae are those within the The mastoid sinuses are air cavities in the mastoid neck. The first vertebra is called the atlas, which artic- process of each temporal bone; they open into the ulates with the occipital bone to support the skull and middle ear. Before the availability of antibiotics, mid- forms a pivot joint with the odontoid process of the dle ear infections often caused mastoiditis, infection of axis, the second cervical vertebra. This pivot joint these sinuses. allows us to turn our heads from side to side. The Within each middle ear cavity are three auditory remaining five cervical vertebrae do not have individ- bones: the malleus, incus, and stapes. As part of the ual names. hearing process (discussed in Chapter 9), these bones The thoracic vertebrae articulate (form joints) transmit vibrations from the eardrum to the receptors with the ribs on the posterior side of the trunk. The in the inner ear (see Fig. 9–7). lumbar vertebrae, the largest and strongest bones of the spine, are found in the small of the back. The sacrum permits the articulation of the two hip bones: VERTEBRAL COLUMN the sacroiliac joints. The coccyx is the remnant of The vertebral column (spinal column or backbone) is tail vertebrae, and some muscles of the perineum made of individual bones called vertebrae. The names (pelvic floor) are anchored to it. 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 120 Copyright © 2007 by F. A. Davis. 120 The Skeletal System B Atlas/Axis Odontoid process 1 2 Vertebral canal 3 Cervical 4 vertebrae Spinous process 5 6 of axis 7 1 2 Facets of atlas for occipital condyles 3 Intervertebral 4 discs 5 C 6 7th Lumbar Thoracic 7 vertebrae 8 9 Transverse process Facet for rib 10 11 Spinous process 12 Vertebral body 1 2 Lumbar 3 D vertebrae 4 1st Lumbar 5 Vertebral Articular surface canal for ilium Sacrum Coccyx Figure 6–10. Vertebral column. (A) Lateral view of left side. (B) Atlas and axis, superior view. (C) 7th thoracic vertebra, left lateral view. (D) 1st lumbar vertebra, left lat- eral view. QUESTION: Compare the size of the individual thoracic A and lumbar vertebrae. What is the reason for this differ- ence? All of the vertebrae articulate with one another in The supporting part of a vertebra is its body; the sequence, connected by ligaments, to form a flexible bodies of adjacent vertebrae are separated by discs backbone that supports the trunk and head. They also of fibrous cartilage. These discs cushion and absorb form the vertebral canal, a continuous tunnel (lined shock and permit some movement between vertebrae with the meninges) within the bones that contains the (symphysis joints). Since there are so many joints, spinal cord and protects it from mechanical injury. the backbone as a whole is quite flexible (see also Box The spinous and transverse processes are projections 6–3: Herniated Disc). for the attachment of the muscles that bend the verte- The normal spine in anatomic position has four bral column. The facets of some vertebrae are small natural curves, which are named after the vertebrae flat surfaces for articulation with other bones, such as that form them. Refer to Fig. 6–10, and notice that the the ribs with the facets of the thoracic vertebrae. cervical curve is forward, the thoracic curve backward, 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 121 Copyright © 2007 by F. A. Davis. BOX 6–3 HERNIATED DISC The vertebrae are separated by discs of fibrous car- The terms herniated disc or ruptured disc more tilage that act as cushions to absorb shock. An inter- accurately describe what happens. The nucleus pul- vertebral disc has a tough outer covering and a soft posus is forced out, often posteriorly, where it puts center called the nucleus pulposus. Extreme pres- pressure on a spinal nerve. For this reason a herni- sure on a disc may rupture the outer layer and force ated disc may be very painful or impair function in the nucleus pulposus out. This may occur when a the muscles supplied by the nerve. person lifts a heavy object improperly, that is, using Healing of a herniated disc may occur naturally if the back rather than the legs and jerking upward, the damage is not severe and the person rests and which puts sudden, intense pressure on the spine. avoids activities that would further compress the Most often this affects discs in the lumbar region. disc. Surgery may be required, however, to remove Although often called a “slipped disc,” the the portion of the nucleus pulposus that is out of affected disc is usually not moved out of position. place and disrupting nerve functioning. Box Figure 6–C Herniated disc. As a result of compression, a ruptured intervertebral disc puts pres- sure on a spinal nerve. 121 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 122 Copyright © 2007 by F. A. Davis. 122 The Skeletal System BOX 6–4 ABNORMALITIES OF THE lages join the 7th rib cartilage. The last two pairs are CURVES OF THE SPINE called floating ribs because they do not articulate with the sternum at all (see Fig. 6–10). An obvious function of the rib cage is that it en- Scoliosis—an abnormal lateral curvature, which may be congenital, the result of having one leg closes and protects the heart and lungs. Keep in mind, longer than the other, or the result of chronic though, that the rib cage also protects organs in the poor posture during childhood while the verte- upper abdominal cavity, such as the liver and spleen. brae are still growing. Usually the thoracic verte- The other important function of the rib cage depends brae are affected, which displaces the rib cage to upon its flexibility: The ribs are pulled upward and one side. In severe cases, the abdominal organs outward by the external intercostal muscles. This may be compressed, and the expansion of the enlarges the chest cavity, which expands the lungs and rib cage during inhalation may be impaired. contributes to inhalation. Kyphosis*—an exaggerated thoracic curve; sometimes referred to as hunchback. THE SHOULDER AND ARM Lordosis*—an exaggerated lumbar curve; sometimes referred to as swayback. The shoulder girdles attach the arms to the axial skele- These abnormal curves are usually the result ton. Each consists of a scapula (shoulder blade) and of degenerative bone diseases such as osteo- clavicle (collarbone). The scapula is a large, flat bone porosis or tuberculosis of the spine. If osteoporo- with several projections (the spine of the scapula, the sis, for example, causes the bodies of the thoracic coracoid process) that anchor some of the muscles that vertebrae to collapse, the normal thoracic curve move the upper arm and the forearm. A shallow will be increased. Most often the vertebral body depression called the glenoid fossa forms a ball-and- “settles” slowly (rather than collapses suddenly) socket joint with the humerus, the bone of the upper and there is little, if any, damage to the spinal arm (Fig. 6–12). nerves. The damage to the vertebrae, however, cannot be easily corrected, so these conditions Each clavicle articulates laterally with a scapula should be thought of in terms of prevention and medially with the manubrium of the sternum. In rather than cure. this position the clavicles act as braces for the scapulae and prevent the shoulders from coming too far for- *Although descriptive of normal anatomy, the terms ward. Although the shoulder joint is capable of a wide kyphosis and lordosis, respectively, are commonly used to range of movement, the shoulder itself must be rela- describe the abnormal condition associated with each. tively stable if these movements are to be effective. The humerus is the long bone of the upper arm. In Fig. 6–12, notice the deltoid tubercle (or tuberosity); the triangular deltoid muscle that caps the shoulder the lumbar curve forward, and the sacral curve back- joint is anchored here. Proximally, the humerus forms ward. These curves center the skull over the rest of the a ball-and-socket joint with the scapula. Distally, the body, which enables a person to more easily walk humerus forms a hinge joint with the ulna of the upright (see Box 6–4: Abnormalities of the Curves of forearm. This hinge joint, the elbow, permits move- the Spine). ment in one plane, that is, back and forth with no lat- eral movement. RIB CAGE The forearm bones are the ulna on the little finger The rib cage consists of the 12 pairs of ribs and the side and the radius on the thumb side. The semilunar sternum, or breastbone. The three parts of the ster- notch of the ulna is part of the hinge joint of the num are the upper manubrium, the central body, and elbow; it articulates with the trochlea of the humerus. the lower xiphoid process (Fig. 6–11). The radius and ulna articulate proximally to form a All of the ribs articulate posteriorly with the tho- pivot joint, which permits turning the hand palm up racic vertebrae. The first seven pairs of ribs are called to palm down. You can demonstrate this yourself by true ribs; they articulate directly with the manubrium holding your arm palm up in front of you, and noting and body of the sternum by means of costal cartilages. that the radius and ulna are parallel to each other. The next three pairs are called false ribs; their carti- Then turn your hand palm down, and notice that your 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 123 Copyright © 2007 by F. A. Davis. The Skeletal System 123 1st rib 1st thoracic vertebra 2nd Manubrium 3rd 4th Body of sternum Costal 5th cartilages 6th 7th 8th Xiphoid process 9th 10th 11th 12th thoracic vertebra 12th Figure 6–11. Rib cage. Anterior view. QUESTION: With what bones do all of the ribs articulate? upper arm does not move. The radius crosses over the THE HIP AND LEG ulna, which permits the hand to perform a great vari- ety of movements without moving the entire arm. The pelvic girdle (or pelvic bone) consists of the two The carpals are eight small bones in the wrist; hip bones (coxae or innominate bones), which articu- gliding joints between them permit a sliding move- late with the axial skeleton at the sacrum. Each hip ment. The carpals also articulate with the distal ends bone has three major parts: the ilium, ischium, and of the ulna and radius, and with the proximal ends of pubis, and these are shown in Fig. 6–13, which depicts the metacarpals, the five bones of the palm of the both a male and a female pelvis. The ilium is the hand. All of the joints formed by the carpals and flared, upper portion that forms the sacroiliac joint. metacarpals make the hand very flexible at the wrist The ischium is the lower, posterior part that we sit (try this yourself: flexion to extension should be almost on. The pubis is the lower, most anterior part. The 180 degrees), but the thumb is more movable than the two pubic bones articulate with one another at the fingers because of its carpometacarpal joint. This is a pubic symphysis, with a disc of fibrous cartilage saddle joint, which enables the thumb to cross over between them. Notice the pubic angle of both the the palm, and permits gripping. male and female pelvises in Fig. 6–13. The wider The phalanges are the bones of the fingers. There female angle is an adaptation for childbirth, in that it are two phalanges in each thumb and three in each helps make the pelvic outlet larger. of the fingers. Between phalanges are hinge joints, The acetabulum is the socket in the hip bone that which permit movement in one plane. Important forms a ball-and-socket joint with the femur. parts of the shoulder and arm bones are described Compared to the glenoid fossa of the scapula, the in Table 6–3. acetabulum is a much deeper socket. This has great 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 124 Copyright © 2007 by F. A. Davis. Acromial end Acromicon process Clavicle Coracoid process Head Sternal end Glenoid fossa Deltoid tubercle Scapula Humerus Capitulum Trochlea Head Semilunar notch On posterior side Olecranon process Radial tuberosity Radius Ulna Scaphoid Lunate Trapezium Carpals Triquetrum Trapezoid Carpals Pisiform Capitate Hamate Metacarpals Phalanges Figure 6–12. Bones of arm and shoulder girdle. Anterior view of right arm. QUESTION: What types of joints are found in the arm? Begin at the shoulder and work downward. 124 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 125 Copyright © 2007 by F. A. Davis. The Skeletal System 125 Table 6–3 BONES OF THE SHOULDER AND ARM—IMPORTANT PARTS Bone Part Description Scapula Glenoid fossa Depression that articulates with humerus Spine Long, posterior process for muscle attachment Acromion process Articulates with clavicle Clavicle Acromial end Articulates with scapula Sternal end Articulates with manubrium of sternum Humerus Head Round process that articulates with scapula Deltoid tubercle Round process for the deltoid muscle Olecranon fossa Posterior, oval depression for the olecranon process of the ulna Capitulum Round process superior to radius Trochlea Concave surface that articulates with ulna Radius Head Articulates with the ulna Ulna Olecranon process Fits into olecranon fossa of humerus Semilunar notch “Half-moon” depression that articulates with the trochlea of ulna Carpals (8) Scaphoid Lunate Proximal row Triquetrum Pisiform Trapezium Trapezoid Distal row Capitate Hamate functional importance because the hip is a weight- fibula is important in that leg muscles are attached and bearing joint, whereas the shoulder is not. Because the anchored to it, and it helps stabilize the ankle. Two acetabulum is deep, the hip joint is not easily dislo- bones on one is a much more stable arrangement than cated, even by activities such as running and jumping one bone on one, and you can see that the malleoli of (landing), which put great stress on the joint. the tibia and fibula overlap the sides of the talus. The The femur is the long bone of the thigh. As men- tibia and fibula do not form a pivot joint as do the tioned, the femur forms a very movable ball-and- radius and ulna in the forearm; this also contributes to socket joint with the hip bone. At the proximal end of the stability of the lower leg and foot and the support the femur are the greater and lesser trochanters, large of the entire body. projections that are anchors for muscles. At its distal The tarsals are the seven bones in the ankle. As end, the femur forms a hinge joint, the knee, with the you would expect, they are larger and stronger than tibia of the lower leg. Notice in Fig. 6–14 that each the carpals of the wrist, and their gliding joints do not bone has condyles, which are the rounded projections provide nearly as much movement. The largest is the that actually form the joint. The patella, or kneecap, calcaneus, or heel bone; the talus transmits weight is anterior to the knee joint, enclosed in the tendon of between the calcaneus and the tibia. Metatarsals are the quadriceps femoris, a large muscle group of the the five long bones of each foot, and phalanges are thigh. the bones of the toes. There are two phalanges in the The tibia is the weight-bearing bone of the lower big toe and three in each of the other toes. The pha- leg. You can feel the tibial tuberosity (a bump) and langes of the toes form hinge joints with each other. anterior crest (a ridge) on the front of your own leg. Because there is no saddle joint in the foot, the big toe The medial malleolus, what we may call the “inner is not as movable as the thumb. The foot has two ankle bone,” is at the distal end. Notice in Fig. 6–14 major arches, longitudinal and transverse, that are that the fibula is not part of the knee joint and does supported by ligaments. These are adaptations for not bear much weight. The lateral malleolus of the walking completely upright, in that arches provide for fibula is the “outer ankle bone” you can find just above spring or bounce in our steps. Important parts of hip your foot. Though not a weight-bearing bone, the and leg bones are described in Table 6–4. (text continued on page 128) 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 126 Copyright © 2007 by F. A. Davis. Figure 6–13. Hip bones and sacrum. (A) Male pelvis, anterior view. (B) Male pelvis, lat- eral view of right side. (C) Female pelvis, anterior view. (D) Female pelvis, lateral view of right side. QUESTION: Compare the male and female pelvic inlets. What is the reason for this differ- ence? 126 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 127 Copyright © 2007 by F. A. Davis. Acetabulum Pubis Head Ischium Greater trochanter Neck Lesser trochanter Femur Patella Medial condyle Lateral condyle Medial condyle Lateral condyle Head Tibial tuberosity Anterior crest Tibia Fibula Tibia Fibula Talus Medial malleolus Talus Lateral malleolus Navicular Calcaneus Tarsals Calcaneus Cuneiforms Cuboid Tarsals First Metatarsals Second Third Phalanges Metatarsals Cuboid Phalanges B A Figure 6–14. (A) Bones of the leg and portion of hip bone, anterior view of left leg. (B) Lateral view of left foot. QUESTION: What types of joints found in the arm do not have counterparts in the leg? 127 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 128 Copyright © 2007 by F. A. Davis. 128 The Skeletal System Table 6–4 BONES OF THE HIP AND LEG—IMPORTANT PARTS Bone Part Description Pelvic (2 hip bones) Ilium Flared, upper portion Iliac crest Upper edge of ilium Posterior superior iliac spine Posterior continuation of iliac crest Ischium Lower, posterior portion Pubis Anterior, medial portion Pubic symphysis Joint between the 2 pubic bones Acetabulum Deep depression that articulates with femur Femur Head Round process that articulates with hip bone Neck Constricted portion distal to head Greater trochanter Large lateral process for muscle attachment Lesser trochanter Medial process for muscle attachment Condyles Rounded processes that articulate with tibia Tibia Condyles Articulate with the femur Tibial tuberosity Round process for the patellar ligament Anterior crest Vertical ridge Medial malleolus Distal process; medial “ankle bone” Fibula Head Articulates with tibia Lateral malleolus Distal process; lateral “ankle bone” Tarsals (7) Calcaneus Heel bone Talus Articulates with calcaneus and tibia Cuboid, navicular — Cuneiform: 1st, 2nd, 3rd — a strong sheath, like a sleeve. Lining the joint capsule JOINTS—ARTICULATIONS is the synovial membrane, which secretes synovial fluid into the joint cavity. Synovial fluid is thick and A joint is where two bones meet, or articulate. slippery and prevents friction as the bones move. Many synovial joints also have bursae (or bursas), THE CLASSIFICATION OF JOINTS which are small sacs of synovial fluid between the joint The classification of joints is based on the amount and the tendons that cross over the joint. Bursae per- of movement possible. A synarthrosis is an immovable mit the tendons to slide easily as the bones are moved. joint, such as a suture between two cranial bones. If a joint is used excessively, the bursae may become An amphiarthrosis is a slightly movable joint, such inflamed and painful; this condition is called bursitis. as the symphysis joint between adjacent vertebrae. A Some other disorders of joints are described in Box diarthrosis is a freely movable joint. This is the largest 6–5: Arthritis. category of joints and includes the ball-and-socket joint, the pivot, hinge, and others. Examples of each type of joint are described in Table 6–5, and many of AGING AND THE SKELETAL SYSTEM these are illustrated in Fig. 6–15. With age, bone tissue tends to lose more calcium than is replaced. Bone matrix becomes thinner, the bones SYNOVIAL JOINTS themselves more brittle, and fractures are more likely All diarthroses, or freely movable joints, are synovial to occur with mild trauma. joints because they share similarities of structure. A Erosion of the articular cartilages of joints is also a typical synovial joint is shown in Fig. 6–16. On the common consequence of aging. Joints affected include joint surface of each bone is the articular cartilage, weight-bearing joints such as the knees, and active, which provides a smooth surface. The joint capsule, small joints such as those of the fingers. made of fibrous connective tissue, encloses the joint in (text continued on page 131) 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 129 Copyright © 2007 by F. A. Davis. A Ball and socket B Hinge C Pivot Acetabulum of hip bone Odontoid process Head of of axis femur Atlas Trochlea of humerus Semilunar notch of ulna Bodies of vertebra Intervertebral disc Carpals Metacarpal of thumb Trapezium D Gliding F Saddle (carpal) E Symphysis Figure 6–15. Types of joints. For each type, a specific joint is depicted, and a simple diagram shows the position of the joint surfaces. (A) Ball and socket. (B) Hinge. (C) Pivot. (D) Gliding. (E) Symphysis. (F) Saddle. QUESTION: Which of these types of joints is most movable? Which is least movable? Table 6–5 TYPES OF JOINTS Category Type and Description Examples Synarthrosis (immovable) Suture—fibrous connective tissue Between cranial bones; between between bone surfaces facial bones Amphiarthrosis (slightly Symphysis—disc of fibrous cartilage Between vertebrae; between pubic movable) between bones bones Diarthrosis (freely movable) Ball and socket—movement in all Scapula and humerus; pelvic bone planes and femur Hinge—movement in one plane Humerus and ulna; femur and tibia; between phalanges Condyloid—movement in one plane Temporal bone and mandible with some lateral movement Pivot—rotation Atlas and axis; radius and ulna Gliding—side-to-side movement Between carpals Saddle—movement in several planes Carpometacarpal of thumb 129 06Scanlon(p3)-ch06 8/17/06 11:13 AM Page 130 Copyright © 2007 by F. A. Davis. Bone Bursa Synovial membrane Figure