The Skeletal System for Middle School Science

Mar 25

8 min read

The human body is a huge topic! The skeletal system is just one of the body systems that make the human body work. Bones shape our bodies and work with our muscles to help us move. Bones also make red blood cells.

You can check out the pages of my skeletal system unit from Teachers Pay Teachers below. You can also continue on to read more about the skeletal system.

The Skeletal System

The skeletal system is the framework of the human body. It gives structure, supports movement, and protects vital organs. Without a skeleton, the body would be soft and unable to hold its shape. The human skeleton also plays a role in producing blood cells and storing minerals like calcium, which are essential for strong bones and overall health.

How the Skeletal System Supports the Body

The skeletal system is more than just a collection of bones. It provides many important functions that keep the body strong and healthy. Bones act as a support system, giving shape to the body and protecting important organs. The skeleton also helps with movement by working with muscles. Inside some bones, a soft tissue called bone marrow produces blood cells, which carry oxygen and fight disease. Additionally, bones store minerals like calcium and phosphorus, which help keep them strong.

Support: Bones provide structure and shape to the body.
Protection: The skull protects the brain, the ribcage protects the heart and lungs, and the spine protects the spinal cord.
Movement: Bones work with muscles to help the body move.
Blood Cell Production: Bone marrow inside certain bones produces red and white blood cells.
Mineral Storage: Bones store calcium and phosphorus, which help keep bones strong.

Parts of the Skeletal System

The skeletal system is made up of bones, joints, and connective tissues that help the body move and function properly. Bones provide structure, while joints allow flexibility. Cartilage, a rubbery tissue found in joints, helps bones move smoothly and prevents them from rubbing against each other. Ligaments are strong bands that connect bones together, and tendons attach muscles to bones, allowing movement. Each part of the skeletal system works together to support the body and help it function.

Bones: Hard structures that form the skeleton.
Joints: Places where two or more bones meet, allowing movement.
Cartilage: A flexible, rubbery tissue that cushions joints and helps them move smoothly.
Ligaments: Strong bands of tissue that connect bones to each other.
Tendons: Connect muscles to bones, helping with movement.

Major Bones of the Human Body

The human body has 206 bones, each with a unique function. Some bones, like the skull and ribcage, protect important organs, while others, like the femur and humerus, help with movement. The skull protects the brain, while the spine supports the body and shields the spinal cord. The ribcage keeps the heart and lungs safe. The pelvis supports the lower body, and the femur, the longest bone in the body, helps with walking and running. Bones in the arms and legs, like the humerus (upper arm bone) and tibia (shin bone), also play key roles in movement.

Skull: Protects the brain.
Spine: Supports the body and protects the spinal cord.
Ribcage: Protects the heart and lungs.
Pelvis: Supports the lower body and helps with movement.
Femur: The thigh bone, which is the longest and strongest bone in the body.
Humerus: The upper arm bone.
Radius and Ulna: The two bones in the forearm.
Tibia and Fibula: The lower leg bones.

Types of Bones

Long Bones – Built for Strength and Movement

Long bones are longer than they are wide and act as levers to help the body move. They contain bone marrow, which produces red blood cells.

Where are they found?

Legs: Femur (thigh bone), tibia (shin bone), fibula
Arms: Humerus (upper arm), radius and ulna (forearm bones)
Hands & Feet: Metacarpals (hand bones), metatarsals (foot bones), phalanges (finger and toe bones)

The femur is the longest and strongest bone in the body, supporting your entire body weight when you stand, walk, or jump!

Short Bones – Small but Strong

Short bones are almost cube-shaped and provide stability and support while allowing limited movement. They are spongy inside, which helps absorb shock.

Where are they found?

Wrists: Carpals (small wrist bones)
Ankles: Tarsals (small ankle bones)

Even though they are small, short bones are very strong and help protect delicate joints from impact, like when you jump or catch yourself after a fall!

Flat Bones – Protectors of the Body

Flat bones are thin, flat, and often curved, providing a large surface for muscles to attach and protecting internal organs.

Where are they found?

Skull: Protects the brain
Ribs & Sternum: Shield the heart and lungs
Scapula (Shoulder Blade): Connects the arms to the body

The skull is actually made up of multiple flat bones that fuse together as you grow! Babies have soft spots in their skulls where the bones haven’t fully joined yet.

Irregular Bones – Uniquely Shaped for Special Jobs

Irregular bones have complex shapes that don’t fit into the other categories. Their unusual shapes allow them to perform specific functions, such as protecting the nervous system or supporting body movement.

Where are they found?

Spine: Vertebrae (bones of the spinal column)
Face & Jaw: Mandible (jawbone), maxilla (upper jaw)
Hips: Pelvis (supports the weight of the upper body)

The vertebrae in your spine help you stand upright, bend, and twist, making them essential for movement!

Sesamoid Bones – Tiny Bones That Reduce Stress

Sesamoid bones are small, round bones embedded within tendons. They help reduce friction in joints and allow smooth movement of muscles.

Where are they found?

Kneecap: Patella (largest sesamoid bone, protects the knee joint)
Hands & Feet: Small sesamoid bones help with movement

Unlike other bones, sesamoid bones develop inside tendons rather than connecting to other bones!

Parts of Bones

Bones may look solid from the outside, but they are actually complex living structures that grow, repair themselves, and help keep the body strong. Each bone has several layers and parts, each with an important role.

1. Periosteum – The Protective Outer Layer

The periosteum is a thin, tough membrane that covers the outside of the bone. It contains nerves and blood vessels, which help provide nutrients to the bone and sense pain when a bone is injured.

✔️ Protects the bone

✔️ Helps with bone growth and repair

✔️ Provides nutrients through blood vessels

Even though bones seem hard and lifeless, they are actually alive! The periosteum contains special cells that help bones heal when they are broken.

2. Compact Bone – The Strong, Hard Layer

Beneath the periosteum is the compact bone, which is the hardest and densest part of the bone. It looks solid but actually contains tiny canals that allow blood to flow through.

✔️ Provides strength and structure

✔️ Supports the body's weight

✔️ Protects the inner parts of the bone

Compact bone is made mostly of calcium and phosphorus, which give bones their hardness. Drinking milk and eating leafy greens can help keep bones strong!

3. Spongy Bone – The Lightweight, Flexible Layer

Deep inside the bone, the spongy bone looks like a honeycomb with many small holes. These spaces help make the bone lighter while still being strong.

✔️ Absorbs shock and reduces weight

✔️ Helps bones resist breaking

✔️ Supports bone marrow

The spongy bone isn’t actually soft—it’s still firm but has a porous, sponge-like structure that makes bones both strong and flexible!

4. Bone Marrow – The Blood Cell Factory

Inside the hollow spaces of many bones is bone marrow, a soft, jelly-like tissue that makes blood cells. There are two types of bone marrow:

Red marrow: Produces red and white blood cells and platelets
Yellow marrow: Stores fat for energy

✔️ Produces red blood cells (carry oxygen)

✔️ Produces white blood cells (fight infections)

✔️ Produces platelets (help blood clot)

A newborn baby’s bones have only red marrow, but as people grow, some of it turns into yellow marrow!

5. Cartilage – The Cushion Between Bones

Cartilage is a smooth, flexible tissue found at the ends of bones. It acts like a cushion to prevent bones from rubbing against each other.

✔️ Protects bones from wear and tear

\✔️ Allows smooth joint movement

✔️ Supports flexible structures (like your nose and ears!)

Unlike bones, cartilage does not contain blood vessels. That’s why injuries to cartilage take longer to heal than broken bones!

How the Skeletal System Interacts with Other Body Systems

The skeletal system does not work alone—it interacts with many other systems in the body. The muscular system attaches to bones to create movement. The nervous system sends signals through the brain and spinal cord, which are protected by bones, to control body movements. The circulatory system relies on bone marrow to produce blood cells, which carry oxygen and fight infections. The digestive system benefits from the minerals stored in bones, like calcium, which helps muscles contract and keeps bones strong. Without the skeletal system, these other body systems would not be able to function properly.

Muscular System: Muscles attach to bones to create movement.
Nervous System: The brain and spinal cord (protected by bones) send signals that control body movement.
Circulatory System: Bone marrow produces blood cells that carry oxygen and fight disease.
Digestive System: Bones store minerals like calcium, which are important for muscle contractions and other body functions.

Skeletal Systems in Other Animals

Not all animals have skeletons like humans. While vertebrates, such as mammals, birds, and fish, have internal skeletons, other animals have evolved different types of skeletal structures. Some creatures have exoskeletons, which are hard outer shells, while others have hydrostatic skeletons, which rely on fluid pressure to move. The way an animal’s skeleton is structured depends on its environment and how it needs to move.

Endoskeleton (Internal Skeleton)

Animals with internal skeletons, called endoskeletons, include mammals, birds, reptiles, amphibians, and fish. Their bones provide strong support and allow them to grow larger than animals with exoskeletons. The endoskeleton is made of bones or cartilage and helps protect internal organs while allowing movement.

Exoskeleton (External Skeleton)

Some animals, like insects, crabs, and spiders, have exoskeletons, which are hard outer shells made of chitin. This tough covering protects their bodies and provides support. However, because exoskeletons do not grow, these animals must shed (molt) their exoskeletons and form new ones as they get bigger.

Hydrostatic Skeleton (Fluid-Based Support)

Soft-bodied animals, like octopuses, do not have bones. Instead, they have hydrostatic skeletons, which use fluid pressure to move. Their bodies are flexible, allowing them to squeeze through small spaces.

Animals Without a Skeleton

Some animals do not have any kind of skeleton at all. These creatures rely on muscle movement and other adaptations to survive. Jellyfish are mostly made of water and use their soft, flexible bodies to move through the ocean. Flatworms have no bones but use their muscles to glide through their environment. Slugs and snails do not have an internal skeleton, but snails have a hard shell that offers some protection. These animals show that not all creatures need bones to survive!

The skeletal system is an essential part of many living things. Whether an animal has bones, a shell, or no skeleton at all, each organism has adaptations that help it move, grow, and survive in its environment.

Flashcards on the Skeletal System and Muscular System

Flashcards are the best way to practice remembering new information. You can get digital and printable flashcards at Teachers Pay Teachers, or you can use the flashcards here for free!