1. The Skeletal System
How is it possible for you to perform motions such as stretching and rolling your shoulders?
The interaction of bones and muscles allows you to perform these motions.

2. In this lesson, you will learn to:
Lesson Objectives
In this lesson, you will learn to:
Describe the functions of the skeletal system
Identify the main divisions and types of bones of the skeletal system

3. Functions of the Skeletal System
What Does Your Skeletal System Do?
Your skeletal system protects your internal tissues and organs from trauma.
The skull, vertebrae, and ribs create protective cavities for the brain, the spinal cord, and the heart and lungs, respectively.
Bones store minerals such as calcium and phosphorus, which are important to the health and strength of the skeleton and to various essential processes in your body.
Bone marrow, a connective tissue within bones, produces new red blood cells and white blood cells.

4. Structure of the Skeleton
The Axial and Appendicular Skeletons
Your skeletal system consists of 206 bones that can be classified in two main groups:
Axial skeleton
Appendicular skeleton

5. Structure of the Skeleton
The Skeletal System

6. Structure of the Skeleton
Types of Bones
All bones are covered with an outer layer of hard, densely packed, compact bone, beneath which is spongy bone filled with red bone marrow.
Almost every bone in the body can be categorized by shape:
Long bones
Short bones
Flat bones
Irregular bones

7. Structure of the Skeleton
Long Bones
The humerus is the bone in your upper arm.
The diaphysis, or main column of a long bone, is composed of compact bone.
Within the diaphysis is a narrow cavity that contains yellow bone marrow.
The end of a long bone is called the epiphysis.
Humerus

8. Structure of the Skeleton
Short Bones
Short bones are almost equal in length and width.
Wrist

9. Structure of the Skeleton
Flat Bones
Flat bones are somewhat thinner and much flatter than other bones.
Flat bones, such as those in the skull, protect organs.
Rib
Irregular Bones
Irregularly shaped bones have unusual shapes and do not fit into the other categories.

10. Structure of the Skeleton
Cartilage
In some joints, such as the knee, cartilage acts as a cushion, reducing friction and allowing smooth motion.
An embryo’s skeleton consists mostly of cartilage that serves as a template from which bones will form.
Early in embryonic development, the cartilage hardens, which is called ossification.

11. Structure of the Skeleton
Joints
Some joints, such as those between the bones of the skull, do not move.
Others, including the joints between vertebrae, have limited movement.
Ligaments help stabilize the movements of bones at a joint.
Movement is produced because muscles are attached to bones by tendons and ligaments.

12. Structure of the Skeleton
Classification of Flexible Joints
Hip (ball-and-socket joint)
Ball-and-socket joints allow the widest range of movement in all directions.
Hinge joints allow a joint to bend and straighten, promoting rotation.
Pivot joints allow limited rotation or turning of the head.
Ellipsoidal joints allow bones to slide over one another.
Knee (hinge joint)

13. Q. _______ is a strong, flexible connective tissue.
Quick Review
Choose the appropriate option.
Q. _______ is a strong, flexible connective tissue.
Cartilage
A ligament
An axial skeleton
4. A tendon

14. A. 1. cartilage Quick Review - Answer
Cartilage is a strong, flexible connective tissue.
Click Next to attempt another question.

15. Q. Which of the following is NOT a function of the skeletal system?
Quick Review
Q. Which of the following is NOT a function of the skeletal system?
To support the upper body and head
To provide a strong, stable, and mobile framework on which muscles can act
To connect the eyes and the brain with the heart and the lungs
To protect the internal tissues and organs from trauma

16. A. 3. To connect the eyes and the brain with the heart and the lungs
Quick Review - Answer
A. 3. To connect the eyes and the brain with the heart and the lungs
The skeletal system does not connect the eyes and the brain with the heart and the lungs.
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17. Q. Which of the following is NOT a type of joint?
Quick Review
Q. Which of the following is NOT a type of joint?
Ball-and-socket joints: e.g., hip or shoulder joints
Roller joints: e.g., inner shoulder joints that connect the joint to a muscle
Hinge joint: e.g., elbow, knee, ankle, and finger joints
Pivot joints: e.g., top two vertebrae

18. A. 2. roller joints Quick Review - Answer
The following is NOT a type of joint: roller joints, e.g., inner shoulder joints that connect the joint to a muscle.
Click Next to attempt another question.

19. Quick Review
Choose the appropriate option.
Q. The ligament that holds the bones in your forearm together and helps form the pivot joint affects your ability to move your hand and arm.
True
False

20. Quick Review - Answer
A. True. The ligament that holds the bones in your forearm together and helps form the pivot joint affects your ability to move your hand and arm.
Click Next to attempt another question.

21. End of Lesson 1
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22. Structure of the Skeleton
The Axial and Appendicular Skeletons
Your skeletal system consists of 206 bones that can be classified in two main groups:
The axial skeleton consists of the 80 bones of the skull, spine, ribs, vertebrae, and sternum, or breastbone.
Axial skeleton
Appendicular skeleton

23. Structure of the Skeleton
The Axial and Appendicular Skeletons
Your skeletal system consists of 206 bones that can be classified in two main groups:
Axial skeleton
Appendicular skeleton
The appendicular skeleton is composed of 126 bones of the upper and lower limbs, shoulders, and hips.

24. Structure of the Skeleton
Cartilage
In some joints, such as the knee, cartilage acts as a cushion, reducing friction and allowing smooth motion.
An embryo’s skeleton consists mostly of cartilage that serves as a template from which bones will form.
Early in embryonic development, the cartilage hardens, which is called ossification.
Cartilage is a strong, flexible connective tissue.

25. Structure of the Skeleton
Cartilage
In some joints, such as the knee, cartilage acts as a cushion, reducing friction and allowing smooth motion.
An embryo’s skeleton consists mostly of cartilage that serves as a template from which bones will form.
Early in embryonic development, the cartilage hardens, which is called ossification.
Ossification is the process by which bone is formed, renewed, and repaired.

26. Structure of the Skeleton
Joints
A ligament is a band of fibrous, slightly elastic connective tissue that attaches bone to bone.
Some joints, such as those between the bones of the skull, do not move.
Others, including the joints between vertebrae, have limited movement.
Ligaments help stabilize the movements of bones at a joint.
Movement is produced because muscles are attached to bones by tendons and ligaments.

27. Structure of the Skeleton
Joints
Some joints, such as those between the bones of the skull, do not move.
Others, including the joints between vertebrae, have limited movement.
Ligaments help stabilize the movements of bones at a joint.
Movement is produced because muscles are attached to bones by tendons and ligaments.
A tendon is a fibrous cord that attaches muscle to the bone.

28. A. Correct! Cartilage is a strong, flexible connective tissue.
Quick Review - Answer
A. Correct! Cartilage is a strong, flexible connective tissue.
Click Next to attempt another question.

29. Quick Review - Answer
You have answered the question incorrectly. Go back to try again, or click Next to view the correct answer.

30. Quick Review - Answer
A. Correct! The skeletal system does NOT function: to connect the eyes and the brain with the heart and the lungs.
Click Next to attempt another question.

31. Quick Review - Answer
You have answered the question incorrectly. Go back to try again, or click Next to view the correct answer.

32. Quick Review - Answer
A. Correct! The following is NOT a type of joint: roller joints, e.g., inner shoulder joints that connect the joint to a muscle.
Click Next to attempt another question.

33. Quick Review - Answer
You have answered the question incorrectly. Go back to try again, or click Next to view the correct answer.

34. Quick Review - Answer
A. Correct! The ligament that holds the bones in your forearm together and helps form the pivot joint affects your ability to move your hand and arm.
Click Next to attempt another question.

35. Quick Review - Answer
You have answered the question incorrectly. Go back to try again, or click Next to view the correct answer.