Skeletal System

Skeletal System

Middle School

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Learning Objectives

• Identify the five major functions of the skeletal system.

• Differentiate between the axial and appendicular skeletons.

• Describe the structure of a bone, including its different tissues and cells.

• Explain the different types of joints and their movement capabilities.

• Recognize common injuries and diseases of the skeletal system.

Key Vocabulary

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Cartilage

Flexible connective tissue found on bone ends and in joints, providing a smooth surface for movement.

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Ligament

Fibrous connective tissue that connects one bone to another bone, holding joints together.

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Joint

The location in the body where two or more bones meet to allow for movement.

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Bone Marrow

Soft tissue in spongy bone that is responsible for producing new blood cells.

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Ossification

The natural process of bone formation, where soft tissue like cartilage hardens into bone.

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Functions & Divisions of the Skeleton

Axial Skeleton

• The axial skeleton forms the central axis, providing the core structure for your body.

• It includes the skull, the vertebral column or backbone, and the protective rib cage.

• Its main job is to protect vital internal organs like the brain, heart, and lungs.

Appendicular Skeleton

• The appendicular skeleton includes all the bones that are attached to the axial skeleton.

• This division is made up of the arms, legs, shoulder girdle, and pelvic girdle.

• Its primary role is to allow for movement, such as walking, running, and grasping.

Multiple Choice

Which of the following bones belongs to the axial skeleton?

• Femur (leg bone)

• Humerus (arm bone)

• Rib cage

• Pelvic girdle

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The Structure of a Bone

• A tough membrane called the periosteum covers the outside of the bone.

• Beneath the periosteum is a hard, dense layer of compact bone for strength.

• Inside compact bone is a layer of spongy bone with many small spaces.

• These spaces contain red marrow for making blood and yellow marrow for storing fat.

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Multiple Choice

What is the primary function of red bone marrow found in the spaces of spongy bone?

• To store fat for energy

• To produce blood cells

• To make the bone hard and dense

• To cover the outer surface of the bone

Specialized Bone Cells & Homeostasis

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Osteoblasts

• Osteoblasts are responsible for building new bone tissue.

• They create a protein matrix and help absorb minerals from the blood.

• This process stores essential minerals like calcium within your bones for later.

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Osteoclasts

• Osteoclasts are responsible for breaking down old bone tissue.

• This process releases essential minerals like calcium back into the blood.

• This helps maintain the correct mineral balance within your entire body.

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Osteocytes

• Osteocytes are mature bone cells that get trapped within the bone matrix.

• They help to control the activities of both osteoblasts and osteoclasts cells.

• These cells help regulate mineral balance in a process called homeostasis.

Multiple Choice

Which type of specialized bone cell is responsible for building new bone tissue?

• Osteoclast

• Osteocyte

• Osteoblast

• Red blood cell

Types of Joints

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Immovable Joints

• ​These joints are fixed and allow no movement at all.

• ​​They are found where bones have fused together for protection.

• ​An example is the joints between the plates of the skull.

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Partly Movable Joints

• ​These joints permit a very small amount of body movement.

• ​​They provide stability and some flexibility to the body's structure.

• ​The joints in your spine are an example of these.

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Movable Joints

• ​These joints allow for the widest range of body motions.

• ​​Bones are cushioned by cartilage to prevent them from rubbing.

• ​Ligaments are strong bands that connect one bone to another.

Multiple Choice

What is the strong connective tissue that holds bones together in a movable joint?

• Cartilage

• Tendon

• Marrow

• Ligament

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Skeletal Injuries & Diseases

Injuries

• A fracture is simply a break that occurs in a bone.

• Fractures can result from forceful impacts or significant stress on the bone.

• They can also happen from minor incidents if bones are weak.

• It can be simple or compound based on the intensity of injury.

Diseases

• Osteoarthritis is a disease that causes the loss of cartilage between joints.

• Osteoporosis is a condition that causes bones to become weak and break easily.

• Rickets is a childhood condition that softens bones due to vitamin D deficiency.

Multiple Choice

A condition that causes bones to become weak and break easily due to mineral loss is known as:

• Osteoarthritis

• Fracture

• Rickets

• Osteoporosis

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Common Misconceptions

Misconception	Correction
Bones are not living tissue.	Bones are living organs with cells, nerves, and blood vessels.
An adult skeleton is static and unchanging.	Bone tissue is constantly being reshaped to repair damage.
Cartilage is only found in your nose and ears.	Cartilage also covers the ends of bones in your joints.

Multiple Choice

How does the structure of the backbone, being made of 26 separate vertebrae, relate to its primary functions?

• It makes the backbone lighter for easier movement.

• It allows the backbone to bend and twist while still providing central support.

• It provides more surface area for blood cell production.

• It helps the backbone store more calcium than a single bone could.

Multiple Choice

Why is a balanced diet rich in calcium particularly important for preventing osteoporosis in later life?

• Calcium helps cartilage stay flexible.

• The body stores calcium in the bones, and a good diet ensures there is enough to keep them dense and strong.

• Calcium is the main component of red bone marrow.

• A lack of calcium directly causes joints to swell.

Multiple Choice

A patient has a condition that significantly reduces the activity of their osteoclasts. What is the most likely long-term effect on their skeletal system?

• Their bones would become overly dense and brittle, as old bone tissue isn't cleared away.

• Their bones would weaken as new bone tissue could not be formed.

• They would be unable to produce red blood cells.

• Their joints would lose cartilage and become stiff.

Multiple Choice

Which of the following is an example of an immovable joint?

• Knee joint

• Shoulder joint

• Joints in Skull

• Elbow joint 

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Summary

• The skeletal system provides support, protection, movement, and mineral storage.

• It is divided into the axial and the appendicular skeletons.

• Bones are living tissues composed of compact bone, spongy bone, and marrow.

• Specialized cells like osteoblasts and osteoclasts constantly reshape bone tissue.

• Joints are where bones meet, held by ligaments and cushioned by cartilage.

• A healthy diet and exercise are crucial to prevent conditions like osteoporosis.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

• 1

• 2

• 3

• 4