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Name____________________________ Class __________________ Date __________ Chapter Chapter 36# Skeletal, Title Muscular, and Integumentary Systems Summary 36–1 The Skeletal System The skeletal system has several jobs. It supports the body, protects internal organs, allows movement, stores mineral reserves, and provides a site for blood cell formation. The skeleton is divided into two parts. • The axial skeleton is made up of the skull, ribs, and spine. • The appendicular skeleton is made up of all of the bones related to the arms and legs. This includes the bones of the shoulders, hips, hands, and feet. Bones are living tissue. Bones are a solid network of cells and protein fibers surrounded by deposits of calcium salts. The periosteum is a layer of connective tissue that surrounds a typical bone. Under the periosteum is a thick layer of compact bone. A network of tubes called Haversian canals runs through compact bone. These canals hold blood vessels and nerves. Cavities that hold bone marrow are inside the bone. Yellow bone marrow is made up of fat cells. Red bone marrow makes blood cells. The skeleton of an embryo is made mostly of cartilage. Cartilage is a tough but flexible connective tissue. Cartilage is replaced by bone in a process called ossification. Ossification starts before birth and continues until adulthood. A joint is a place where one bone attaches to another. Joints allow bones to move without damaging each other. Depending on its type of movement, a joint is classified as immovable, slightly movable, or freely movable. • Immovable joints allow no movement. Immovable joints are found in the skull. • Slightly movable joints, such those in the spine, allow a small amount of movement. • Freely movable joints permit movement in one or more directions. Four common freely movable joints are: ball-andsocket joints, hinge joints, pivot joints, and saddle joints. Ligaments are strips of tough connective tissue that hold bones together in a joint. The bony surfaces of the joint are covered with cartilage. A substance called synovial fluid forms a thin film on the cartilage, making the joint surfaces slippery. Excessive strain or disease can damage bones and joints. • Arthritis is a disorder that involves inflammation of the joints. • Osteoporosis is a condition in which bones weaken. Weak bones are prone to fracture, or breaking. © Pearson Education, Inc., publishing as Pearson Prentice Hall. 354 Name____________________________ Class __________________ Date __________ 36–2 The Muscular System Working together with the skeletal system, the muscular system produces movement. There are three different types of muscle tissue. • Skeletal muscles most often attach to bones. Skeletal muscles allow voluntary movements such as dancing. • Smooth muscles line blood vessels and the digestive tract. They are not under conscious control. Smooth muscles move food through the digestive tract and control the flow of blood through the circulatory system. • Cardiac muscle is found only in the heart. Cardiac muscle is not under voluntary control. Skeletal muscle cells are called muscle fibers. Muscle fibers are made up of smaller structures called myofibrils. Each myofibril is made up of even smaller structures called filaments. Filaments can be thick or thin. Thick filaments are made of the protein myosin. Thin filaments are made of the protein actin. Thick and thin filaments are arranged in units called sarcomeres. When the muscle is relaxed, there are no thin filaments in the middle of the sarcomere. A musle contracts when the thin filaments in the muscle fiber slide over the thick filaments. During muscle contraction, knoblike heads of myosin filaments attach to binding sites on actin molecules. Each attachment is called a cross-bridge. ATP then causes the myosin cross-bridge to change shape. This change in shape pulls the actin filament toward the center of the sarcomere. The myosin head detaches and the cycle repeats. Tendons join muscles to bones. Tendons pull on bones, making them work like levers. Muscles supply the force that moves bones. Most skeletal muscles work in opposing pairs. When one muscle contracts, the other muscle relaxes. For example, in order to bend the arm at the elbow, the biceps contract and the triceps relax. This creates the force necessary to bend the elbow joint. To extend the arm, the triceps contract and the biceps relax. Regular exercise is important in maintaining muscle strength and flexibility. Regular exercise also strengthens bones. Strong bones and muscles are less likely to be injured. © Pearson Education, Inc., publishing as Pearson Prentice Hall. 355 Name____________________________ Class __________________ Date __________ 36–3 The Integumentary System The integumentary system has several jobs. It covers the body and protects against infection, injury, and ultraviolet radiation. It helps regulate body temperature and removes wastes from the body. The skin is made up of two main layers. • The epidermis is the outer layer of the skin. The epidermis is composed of two layers. The inner layer of the epidermis is made up of living cells. These cells quickly divide and push older cells up toward the surface of the skin. Eventually, the older cells die. The outside layer of the epidermis is made up of dead cells. It provides a tough, flexible, waterproof outer covering for the body. The epidermis also contains cells that produce melanin. Melanin is a dark brown pigment. It helps protect the skin from ultraviolet radiation in sunlight. • The dermis is the inner layer of skin. The dermis contains many different types of structures such as blood vessels, nerve endings, hair follicles, and glands. There are two main types of glands in the dermis: sweat glands and sebaceous glands. Sweat glands produce sweat. Sweat evaporates off of the surface of skin and helps keep the body cool. Sebaceous glands produce sebum. This oily substance helps keep the epidermis flexible and waterproof. Hair and nails are also parts of the integumentary system. Hair and nails are made mainly of keratin. Hair is made by structures called hair follicles. Nails grow from an area called the nail root. Nails protect the tips of the fingers and toes. © Pearson Education, Inc., publishing as Pearson Prentice Hall. 356