Chapter 8 Lesson 2 The Skeletal System Bones and Joints • Bones A bone is an organ of the skeletal system. Bones are hard because they store minerals. • Bone Marrow Inside a bone is soft tissue called bone marrow. Bone marrow makes blood cells for the body. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Joints • Joints A joint is a place where two or more bones meet. • Joints – where bones meet to allow movement – Sliding joints – allow bones in hand to glide over one another – Ball-and-socket joint – enables you arm or leg to move freely in all directions – Hinge joint – enables you to flex and extend elbow and knee. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. • Ligaments attach bones to another bone at the joint. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 8 Lesson 2 The Skeletal System Bone and Joint Development • Cartilage Before birth, most of the bones in a baby’s body are made of cartilage. Cartilage is a soft, flexible tissue. • Bone Formation Cartilage starts changing to bone before a baby is born. The soft tissue hardens and becomes bone tissue as minerals, such as calcium, build up in the bone. This change is not finished until a person is around 18 years old. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. How the Skeletal System Works Label the Skeletal System Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 8 Lesson 3 The Muscular System Many Kinds of Muscles • Skeletal Muscle Skeletal muscle is muscle that is attached to bones. Example: Bicep • Smooth Muscle Smooth muscle is muscle that forms some internal organs. Example: Small Intestine • Cardiac Muscle Cardiac muscle is muscle that forms the heart. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 8 Lesson 3 The Muscular System Muscles and Movement • How Muscles Move Bones When skeletal muscles contract, they pull on bones. When a muscle contracts, its two ends are pulled towards its center. If the two ends are attached to different bones, the bones are pulled towards each other. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 8 Lesson 3 The Muscular System Muscles work in pairs. Here, the biceps and triceps move the bones of the arm by pulling them in opposite directions. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 8 Tendons attach a muscle to a bone at the joint. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 8 How the Muscular System Works Label the Muscular System Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.