1 FOCUS
Objectives
36.1.1 State the functions of the skeletal system.
36.1.2 Describe the structure of a typical bone.
36.1.3 Explain how bones develop. 36.1.4 Identify the three different
kinds of joints.
Vocabulary Preview
Tell students that words beginning with os, the Latin word for bone, have something to do with bone. For example, the word ossification means “the process of bone formation.” Challenge students to find other words beginning with os, such as osteocyte, and explain each word’s connection with bone.Reading Strategy
Have students preview the material in the section by studying the figures and reading the captions. They should make note of any words they do not know and find the definitions as they read the section.
2 INSTRUCT
The Skeleton
Demonstration
Show students a three-dimensional model of the human skeleton. Challenge them to identify the bones of the axial skeleton (skull, vertebral column, rib cage) and the appendicu-lar skeleton (arms, legs, pelvic girdle, pectoral girdle). Allow students to manipulate the bones so that they have a better understanding of how the axial skeleton supports the body and the appendicular skeleton allows movement.
Section 36–1
T
o retain their shapes, all organisms need some type of struc-tural support. Unicellular organisms have a cytoskeleton that provides structural support. In multicellular animals, support is provided by some form of skeleton, including the external exoskeletons of arthropods and the internal endoskel-etons of vertebrates. The human skeleton is composed of a type of connective tissue called bone. Bones and other connective tissues, such as cartilage and ligaments, form the skeletal system.Scientists can infer a lot about the behavior of extinct species by studying fossil bones and reconstructing skeletons. The human skeleton also contains important clues. The shape of your hip bones shows that you walk upright on two legs. The structure of the bones in your hands, especially your opposable thumbs, indicates that you have the ability to grasp objects. The size and shape of your skull is a clue that you have a well-developed brain.
The Skeleton
The skeletal system has many important functions. The skeleton supports the body, protects internal organs, provides for movement, stores mineral reserves, and provides a site for blood cell formation. The bones that
make up the skeletal system support and shape the body much like an internal wooden frame supports a house. Just as a house could not stand without its wooden frame, the human body would collapse without its bony skeleton. Bones protect the delicate internal organs of the body. For example, the skull forms a protective shell around the brain, and the ribs form a basketlike cage that protects the heart and lungs.
Bones provide a system of levers on which muscles act to produce movement. Levers are rigid rods that can be moved about a fixed point. In addition, bones contain reserves of minerals, mainly calcium salts, that are impor-tant to many body processes. Finally, bones are the site of blood cell formation. Blood cells are produced in the soft marrow tissue that fills the internal cavities in some bones.
There are 206 bones in the adult human skeleton. As shown in Figure 36–2
on page 922, these bones can be divided into two parts—the axial skeleton and the appendicular skeleton. The axial skeleton
sup-ports the central axis of the body. It consists of the skull, the vertebral column, and the rib cage. The bones of the arms and legs, along with the bones of the pelvis and shoulder area, form the appendicular skeleton.
Key Concepts
• What are the functions of the skeletal system?
• What is the structure of a typical bone?
• What are the three different kinds of joints? Vocabulary periosteum Haversian canal bone marrow cartilage ossification joint ligament Reading Strategy: Asking Questions Before you read, rewrite the headings in this section as how, why, or
what questions about the
skeletal system. As you read, write brief answers to those heading questions.
왔
Figure 36–1 Bones provide a system of levers on which muscles act to produce movement. Withoutthis coordination, movement would not be possible.
36–1 The Skeletal System
SECTION RESOURCES
Print:
• Laboratory Manual A, Chapter 36 Lab • Teaching Resources, Lesson Plan 36–1,
Adapted Section Summary 36–1, Adapted Worksheets 36–1, Section Summary 36–1, Worksheets 36–1, Section Review 36–1 • Reading and Study Workbook A,
Section 36–1
• Adapted Reading and Study Workbook B, Section 36–1
• Issues and Decision Making,
Issues and
Decisions 38
Technology: • iText, Section 36–1
• Transparencies Plus, Section 36–1
Tim
e
Structure of Bones
It is easy to think of bones as nonliving. After all, most of the mass of bone is mineral salts— mainly calcium and phosphorus. However, bones are living tissue. Bones are a solid net-work of living cells and protein fibers that are surrounded by deposits of calcium salts.
Figure 36–3shows the structure of a typical bone. The bone is surrounded by a tough layer of connective tissue called the (pehr-ee-AHS-tee-um). Blood vessels that pass through the periosteum carry oxygen and nutrients to the bone. Beneath the periosteum is a thick layer of compact bone. Although compact bone is dense, it is far from being solid. Running through compact bone is a network of tubes called
(huh-VUR-zhun) that contain blood vessels and nerves.
A less dense tissue known as spongy bone is found inside the outer layer of compact bone. It is found in the ends of long bones and in the middle part of short, flat bones. Despite its name, spongy bone is not soft and spongy; it is actually quite strong. Near the ends of bones where force is applied, spongy bone is organized into structures that resemble the supporting girders in a bridge. This latticework structure of spongy bone helps to add strength to bone without adding mass.
Osteocytes, which are mature bone cells, are embedded in the bone matrix. Two other kinds of bone cells—osteoclasts (AHS-tee-oh-klasts) and osteoblasts line the Haversian canals and the surfaces of compact and spongy bone. Osteoclasts break down bone. Osteoblasts produce bone. Although we stop growing in our late teens, our bones are continuously remodeled through the activity of osteoclasts and osteoblasts.
Within bones are cavities that contain a soft tissue called There are two types of bone marrow: yellow and red. Yellow marrow is made up primarily of fat cells. Red marrow produces red blood cells, some kinds of white blood cells, and cell fragments called platelets.
Development of Bones
The skeleton of an embryo is composed almost entirely of a type of connective tissue called
The cells that make up cartilage are scattered in a network of protein fibers including both tough collagen and flexible elastin.
cartilage. bone marrow. canals Haversian periosteum Skull Clavicle Scapula Sternum Ribs Vertebral column Humerus Radius Ulna Carpals Metacarpals Phalanges Pelvis Femur Patella Tibia Fibula Tarsals Metatarsals Phalanges Axial Skeleton Appendicular Skeleton
왖
Figure 36–2 The skeleton supports the body.The human skeleton is divided into two parts: the axial skeleton and the appendicular skeleton.
For: Links on bones and joints Visit: www.SciLinks.org Web Code: cbn-0361 NSTA
Structure of Bones
Address Misconceptions
Students may have difficulty conceiv-ing of bone as livconceiv-ing tissue. Ask: Which do you think is a better model of a bone, a stick of chalk or a piece of sponge? (Some students may say that a stick of chalk is a bet-ter model.) Point out that a stick of chalk may look more like a bone, but a piece of sponge is more like a bone in its structure. Both the sponge and the bone contain a network of tubes or spaces through which things can pass. Ask: What passes through the tubes and spaces inside bone? (Blood vessels and nerves)Use Visuals
Figure 36–3 Make sure students understand how the two parts of the figure are related. Point out how the drawing on the right shows a cross section of a tiny piece of the bone on the left. Guide students in using the figure to distinguish between compact and spongy bone tissue. Ask: What structures are found in compact bone? (Haversian canals, veins, arteries, and osteocytes) Where is spongy bone found? (Beneath compact bone at the ends of long bones and in the middle of short, flat bones)
Development of
Bones
Build Science Skills
Comparing and Contrasting Work with the class to create a table comparing and contrasting bone and cartilage. Have a volunteer record the information in a chart on the chalkboard as the class brain-storms the similarities and differences between the two types of tissue.Comprehension: Key Concept
Beginning On the board, rewrite the boldface sentence on page 921 as individual sentences that each express one function of the skeletal system. Then, pair ESL students with students who are proficient in English. Have the student pairs construct a concept circle (cluster dia-gram) with “Functions of the Skeletal System” in the center and the five functions connected to the center by lines.
Intermediate Read aloud the boldface sen-tence on page 921, and write it on the board. Ask individual students, including some ESL students, to identify and describe the functions of the skeletal system. Give students copies of Figure 36–2. Work with students to identify parts of the skeleton that perform specific func-tions, e.g., the skull protects, the femur supports. Have students label the appropriate parts with the functions.
SUPPORT FOR ENGLISH LANGUAGE LEARNERS
36–1
(continued)N S TA
Download a worksheet
on bones and joints for students to complete, and find additional teacher support from NSTA SciLinks.
Unlike bone, cartilage does not contain blood vessels. Cartilage cells must rely on the diffusion of nutrients from the tiny blood vessels in surrounding tissues. Because cartilage is dense and fibrous, it can support weight, despite its extreme flexibility.
Cartilage is replaced by bone during the process of bone for-mation called (ahs-uh-fih-KAY-shun). Ossification begins to take place up to seven months before birth. Bone tissue forms as osteoblasts secrete mineral deposits that replace the cartilage in developing bones. When the osteoblasts become surrounded by bone tissue, they mature into osteocytes.
Many long bones, including those of the arms and legs, have growth plates at either end. The growth of cartilage at these plates causes the bones to lengthen. Gradually, this new growth of cartilage is replaced by bone tissue, and the bones become larger and stronger. During late adolescence or early adulthood, the cartilage in the growth plates is replaced by bone, the bones become completely ossified, and the person “stops growing.”
In adults, cartilage is found in those parts of the body that are flexible, such as the tip of the nose and the external ears. Cartilage also is found where the ribs are attached to the sternum, which allows the rib cage to move during breathing.
What is ossification?
ossification
Haversian Canal (magnification: 200⫻)
Bones are a solid network of living cells and protein fibers that are supported by deposits of calcium salts. A typical long bone such as the femur contains spongy bone and compact bone. Within compact bone are Haversian canals, which contain blood vessels.
Periosteum Periosteum Bone marrow Spongy bone Compact bone Spongy bone Compact bone Artery Vein Haversian canal Osteocyte
F
IGURE36–3
S
TRUCTURE OF A
B
ONE
Make Connections
Health Science Inform students that force must be placed on bone for ossification to occur, because it is force that stimulates the osteoblasts to secrete the minerals that replace cartilage. Ask: What effect do you think an exercise such as walking would have on the bones of the legs? (It would stimulate ossification, so the bones would contain more min-erals and be stronger.) Ask: What do you think might happen to bones that are not exposed to force, such as the bones of astronauts in zero gravity? (The bones would lose miner-als because of lack of force exerted on them, so they would become weaker.)Demonstration
Demonstrate to students that even ossified bones contain a framework of collagen. Bring a clean chicken bone to class and, after pointing out how relatively hard and inflexible it is, place it in a beaker of vinegar to soak. After a few days, remove the bone and invite students to inspect it. They will observe that the bone has become rubbery and flexible. Explain that the vinegar dissolved the calcium (mineral) in the bone, leaving behind the collagen (pro-tein). Ask: What role does collagen play in an ossified bone? (It pro-vides a framework for the minerals in the bone and gives the bone some flexibility.)
When introducing the skeletal system, I go to a local health clinic and obtain a series of X-rays of the joints and bones that will be discussed. Technicians from local clinics are sometimes willing to visit the class and discuss the different X-rays, as well as explain the various aspects of X-ray medicine. As a class, we have also built an
X-ray “skeleton” by mounting the various X-rays on a bulletin board. This “skeleton” is also a very good tool to use in reviewing the chapter.
—Bob Sprang Biology Teacher
Mitchell Senior High School Mitchell, South Dakota
TEACHER TO TEACHER
Answer to . . .
Ossification is the process of bone formation in which cartilage is replaced by bone.
SE page reduction 80%
Clavicle Ball-and-Socket Joint Humerus Scapula Ball-and-socket joint Hinge joint Hinge Joint Fibula Tibia Patella Pivot joint Pivot Joint Humerus Radius Ulna Femur Saddle joint Saddle Joint Carpals Metacarpals왖
Figure 36–4 Freely movable joints are classified by the type of movement they permit. Thejoints illustrated are in the shoulder, knee, elbow, and hand.
Types of Joints
A place where one bone attaches to another bone is called a Joints permit bones to move without damaging each other. Some joints, such as those of the shoulder, allow extensive movement. Others, like the joints of the fully developed skull, allow no movement at all.
Depending on its type of movement, a joint is classified as immovable, slightly movable, or freely movable.
Immovable Joints
Immovable joints, often called fixed joints, allow no movement. The bones at an immovable joint are interlocked and held together by connective tissue, or they are fused. The places where the bones in the skull meet are examples of immovable joints.Slightly Movable Joints
Slightly movable joints permit a small amount of restricted move-ment. Unlike the bones of immovable joints, the bones of slightly movable joints are separated from each other. The joints between the two bones of the lower leg and the joints between adjacent vertebrae are examples of slightly movable joints.Freely Movable Joints
Freely movable joints permit movement in one or more directions. Freely movable joints are grouped according to the shapes of the surfaces of the adjacent bones. The most common types of freely movable joints are shown in Figure 36–4.Ball-and-socket joints permit movement in many directions. They allow the widest range of movement of any joint. Hinge joints permit back-and-forth motion, like the opening and closing of a door. Pivot joints allow one bone to rotate around another. Saddle joints permit one bone to slide in two directions.
What are the four common types of freely movable joints?
joint.
For: Joint Movement activity Visit: PHSchool.com Web Code: cbp-0361
Types of Joints
Build Science Skills
Using Models Provide students with materials such as craft sticks, toothpicks, pipe cleaners, modeling clay, tacks, and glue. Then, challenge them to create models of one or more types of joints shown in Figure 36–4. Invite students to demonstrate their completed models to the class. Ask: What type of joint and what range of motion does your model illustrate? (Models should illustrate the range of motion of one of the four types of joints shown in the figure.) Call on other students to name examples of that type of joint.Demonstration
Ask a volunteer to model the move-ment of several different joints. As you name each joint, have the stu-dent demonstrate the range of motion permitted by the joint. In each case, challenge the rest of the class to name other joints that have the same range of motion.
Structure of Joints
Use Community Resources
Invite a professional from the med-ical community to speak to the class about joints and joint problems. Possible speakers might include a radiology technician, physical thera-pist, chiropractor, or physician’s assistant in sports medicine, rheuma-tology, or orthopedics. Encourage students to prepare questions for the speaker in advance. Afterward, have them write a summary of what they learned.PROGRAM RESOURCES
Bionic joints
Osteoarthritis plagues many older adults, causing them to have stiff, aching joints and keeping them from being as active as they would like. Replacing arthritic joints, especially the hip and knee, with artificial joints made of metal and plas-tic is an increasingly common solution to this problem. The major drawback has been that arti-ficial joints tend to wear out in just 10 to 15 years. Now, a new type of polyethylene is being used to
make artificial joints that last much longer. Machines that test artificial joints by putting them through a million movements a week have con-firmed that the polyethylene joints should last for at least 27 years. Scientists are also researching ways to rebuild aging joints so they will not need to be replaced. For example, they are testing a type of cell that replaces damaged cartilage and a protein paste that helps repair damaged joints.
BIOLOGY UPDATE
36–1
(continued)For: Joint Movement activity Visit: PHSchool.com Web Code: cbe-0361 Students explore the skeletal and muscular systems through various joint movements.
Structure of Joints
In freely movable joints, cartilage covers the surfaces where two bones come together. This protects the bones as they move against each other. The joints are also surrounded by a fibrous joint capsule that helps hold the bones together while still allowing them to move.
The joint capsule consists of two layers. One layer forms strips of tough connective tissue called
Ligaments, which hold bones together in a joint, are attached to the membranes that surround bones. Cells in the other layer of the joint capsule produce a substance called synovial (sin-OH-vee-ul) fluid. Synovial fluid enables the sur-faces of the joint to slide over each other smoothly.
In some freely movable joints, such as the knee in Figure 36–5,small sacs of synovial fluid called bursae (BUR-see; singular: bursa) form. A bursa reduces the friction between the bones of a joint and also acts as a tiny shock absorber.
Skeletal System Disorders
Bones and joints can be damaged, just like any other tissue. Excessive strain on a joint may produce inflammation, a response in which excess fluid causes swelling, pain, heat, and redness. Inflammation of a bursa is called bursi-tis. A more serious disorder is arthritis, which involves inflammation of the joint itself.
In older people, especially women, loss of calcium in the bones can lead to a condition known as osteoporosis. Osteoporosis is a weaken-ing of the bones that can cause serious fractures. Sound nutrition, including plenty of calcium in the diet, and weight-bearing exercise are among the best ways to prevent this serious problem.
ligaments. Muscle Tendon Femur Patella Ligament Bursa Synovial fluid Cartilage Fat Fibula Tibia
왖
Figure 36–5 The knee joint is protected bycartilage and bursae. The ligaments hold the bones composing the knee joint—femur, patella, tibia, and fibula—together. Inferring How do the cartilage and bursae help reduce friction?
1. Key Concept List the different functions of the skeletal system.
2. Key Concept Describe the structure of a typical bone. 3. Key Concept What is a
joint? List the three types of joints.
4. How does compact bone differ from spongy bone?
5.Critical Thinking Inferring Why do you think the amount of cartilage decreases and the amount of bone increases as a person develops?
Creative Writing Use library or Internet resources to find out more about osteoporosis. Then, develop an advertising campaign for the dairy industry based on the relationship between milk and healthy bone development.
36–1 Section Assessment
Skeletal System
Disorders
Make Connections
Health Science Point out that there are several different types of arthritis, including rheumatoid arthritis and osteoarthritis, also called degenerative joint disease. Challenge students to identify ways in which the two types differ. (Possible answers: rheumatoid arthritis is caused by the immune system attacking joints and usually occurs by young adulthood; osteoarthritis is caused by wear and tear on joints and usually occurs after middle age.)
3 ASSESS
Evaluate Understanding
Read each of the Vocabulary words in the section. As you read, call on stu-dents at random to define the terms without referring to their books.Reteach
Work with students to make a table summarizing the similarities and dif-ferences among the different types of joints. Label the columns: Type of Joint, Range of Motion, Examples.
If your class subscribes to the iText, use it to review the Key Concepts in Section 36–1.
Answers to . . .
Ball-and-socket, hinge, pivot, and saddle
Figure 36–5 They help reduce fric-tion by providing a smooth, flexible surface between bones in joints.
Students’ advertising campaigns should make a convincing argument for milk consumption that includes information regarding the high inci-dence of osteoporosis at older ages, especially in women; the serious potential health consequences of osteoporosis, including broken bones; the role of dietary calcium in preventing osteoporosis; and the high calcium content of milk.
36–1 Section Assessment
1. The skeletal system supports the body,pro-tects internal organs, allows movement, stores mineral reserves, and provides a site for blood cell formation.
2. A typical bone has a thick layer of compact bone covered by periosteum. Haversian canals contain the blood vessels and nerves. At the ends of long bones, there is a layer of spongy bone beneath the compact bone layer.
3. A joint is a place where one bone attaches to another. Three types of joints are immovable, slightly movable, and freely movable. 4. Compact bone is denser than spongy bone.
Spongy bone is found in the ends of long bones and in the middle of short, flat bones. 5. The cartilage decreases because minerals
