3.36 Parts of the Skeletal System

Learn about the skeletal system and the parts of the skeletal system. In addition to bones, discover the cartilage and ligament tissues that also play important roles, and explore the function of the skeleton and different types of joints.

The Skeletal System

Did you know that a baby has more bones than an adult? Babies are born with about 300 bones. By adulthood, some of those bones become fused, which means they join together. An adult ends up with 206 bones, and these bones make up the bulk of the skeletal system. Now, let’s discuss the bones and other parts of the skeletal system, including your joints, ligaments and cartilage.

1. Main points:

Babies are born with more bones than adults, having about 300 bones that fuse to become 206 by adulthood, forming the skeletal system including joints, ligaments, and cartilage.

2. Questions:

• Content Analysis: How many bones are babies born with, and how does this number change by adulthood?
• Contextual Analysis: Why is the information about bones fusing important in understanding the skeletal system?
• Linguistic Analysis: What words in the text indicate a change or transformation?

3. Further Discussion:

If you were to explain to a friend why babies have more bones than adults, what would you say?

4. Answers:

• Content Analysis: "Babies are born with about 300 bones. By adulthood, some of those bones become fused… An adult ends up with 206 bones."
• Contextual Analysis: The text explains that "some of those bones become fused, which means they join together."
• Linguistic Analysis: The words "fused" and "join together" indicate a change or transformation in the number of bones from babyhood to adulthood.

Bones of the Skeleton

Axial skeleton

The human skeleton is split into two parts: the axial skeleton and the appendicular skeleton. If you drew a line down the center of your body, you’d touch most of the bones of your axial skeleton.

Your skull, rib cage and spine are all part of the axial skeleton. These bones act like builtin armorthey form around delicate organs, like your brain, heart, lungs and spinal cord, to protect them from damage.

The bones of your legs and arms make up your appendicular skeleton. These bones are connected to each other by freely movable joints. The bones and joints of your appendicular skeleton make running, throwing a ball and dancing possible.

Bones do a lot of things for you. We already learned that they protect delicate organs and allow for movement. The bone marrow found inside of bones makes blood cells.

And, we can’t forget that bones support your body so you can stand up straight. Without bones, you would be a blob and have to creep along the ground like a slug!

1. Main points:

The human skeleton is divided into the axial skeleton (including the skull, rib cage, and spine) and the appendicular skeleton (bones of the arms and legs), with bones providing protection, support, and enabling movement.

2. Questions:

• Content Analysis: What are the main functions of the bones in the human body?
• Contextual Analysis: How does the division of the skeleton into axial and appendicular parts relate to its overall function?
• Linguistic Analysis: What words or phrases in the text create a vivid image or comparison?

3. Further Discussion:

Can you think of any activities that would be difficult or impossible without our appendicular skeleton?

4. Answers:

• Content Analysis: "They protect delicate organs and allow for movement. The bone marrow found inside of bones makes blood cells."
• Contextual Analysis: "Your skull, rib cage and spine are all part of the axial skeleton… The bones of your legs and arms make up your appendicular skeleton."
• Linguistic Analysis: The phrase "Without bones, you would be a blob and have to creep along the ground like a slug!" creates a vivid comparison.

Joints

The place where bones come together is called a joint. Some joints allow a lot of movement, like the joints in your arms and legs. Other joints are held together tightly, like the joints in your skull.

Joints can be injured when you play sports. For example, a separated shoulder is an injury to the joint that holds the arm bone and shoulder together.

1. Main points:

Joints are where bones meet, allowing for movement or being held tightly, and they can be injured during activities like sports, such as a separated shoulder.

2. Questions:

• Content Analysis: What are the two types of joints mentioned in the text and what are their characteristics?
• Contextual Analysis: How does playing sports relate to joint injuries?
• Linguistic Analysis: What words in the text indicate the function or importance of joints?

3. Further Discussion:

Why do you think some joints in our body allow a lot of movement while others do not?

4. Answers:

• Content Analysis: "Some joints allow a lot of movement, like the joints in your arms and legs. Other joints are held together tightly, like the joints in your skull."
• Contextual Analysis: "Joints can be injured when you play sports."
• Linguistic Analysis: Words like "movement" and "held together tightly" indicate the function and importance of joints.

Ligaments

Ligaments of the knee

Ligaments are strong bands of tissue. Many joints are held together by ligaments. These bands also limit motion in some of your joints.

You can understand what your ligaments do by doing an experiment. First, bend your knee as tight as you can. Now, straighten it. That movement is easy to do.

Now, try to bend your knee the other way. No matter how hard you try, your knee only bends in one direction. Ligaments in your knee prevent unwanted movements (after all, bending the knee in the opposite direction could cause it to break).

1. Main points:

Ligaments are strong tissue bands that hold joints together and limit their motion, preventing movements that could be harmful, like bending a knee in the wrong direction.

2. Questions:

• Content Analysis: What is the primary function of ligaments in the human body?
• Contextual Analysis: How does the experiment with bending the knee help in understanding the role of ligaments?
• Linguistic Analysis: What words or phrases in the text emphasize the protective role of ligaments?

3. Further Discussion:

Can you think of any other body parts where ligaments play a crucial role?

4. Answers:

• Content Analysis: "Ligaments in your knee prevent unwanted movements."
• Contextual Analysis: "You can understand what your ligaments do by doing an experiment. First, bend your knee as tight as you can. Now, straighten it… try to bend your knee the other way."
• Linguistic Analysis: The phrase "prevent unwanted movements" and "bending the knee in the opposite direction could cause it to break" emphasize the protective role of ligaments.

Cartilage

Cartilage is a slipper covering on the ends of bones. Cartilage makes the ends of the bones smooth and prevents the bones from rubbing against each other.

A baby’s skeleton has more cartilage than an adult. Did you ever feel the soft spot on a baby’s head? That soft spot is cartilage. It allows the baby’s skull to flex and squeeze through the birth canal. Hard bone later replaces the soft cartilage.

1. Main points:

Cartilage is a slippery substance on bone ends, preventing bone friction, and is more abundant in babies, like the soft spot on a baby’s head, allowing skull flexibility during birth before being replaced by bone.

2. Questions:

• Content Analysis: What are the main functions of cartilage in the human body?
• Contextual Analysis: Why does a baby’s skeleton have more cartilage compared to an adult?
• Linguistic Analysis: What words in the text describe the texture and role of cartilage?

3. Further Discussion:

How do you think the presence of cartilage affects our daily movements?

4. Answers:

• Content Analysis: "Cartilage makes the ends of the bones smooth and prevents the bones from rubbing against each other."
• Contextual Analysis: "It allows the baby’s skull to flex and squeeze through the birth canal. Hard bone later replaces the soft cartilage."
• Linguistic Analysis: Words like "slippery," "smooth," and "prevents… rubbing" describe the texture and role of cartilage.

Lesson Summary

Your skeletal system is made up of hundreds of bones and works to protect your body and give it structure. Your skill, rib cage and spine are all part of the axial skeleton, while leg bones and arms make up the appendicular skeleton.

At the ends of bones is cartilage, a covering that protects the bones from grinding against each other. The place where bones come together is called a joint. Many joints are held together by ligaments, which are strong bands of tissue.