Skeletal system

The skeletal system gives our bodies shape and support. Learning how it works helps us understand how our bodies move and stay strong. Use this resource to explore parts of the skeletal system and what they do. Also learn about a culturally responsive movement-based program to improve health outcomes, including skeletal health, for Aboriginal and Torres Strait Islander children.

Musculoskeletal system

The musculoskeletal system or locomotor system includes the bones, muscles, tendons and ligaments in the body. They work together to:

• keep us upright
• help us move
• protect our organs
• make new red and white blood cells
• store important minerals.

It consists of the skeletal and muscular systems. Here, we will look at the skeletal system. The next page will discuss the muscular system.

The skeleton

The skeletal system consists of all the bones in the body and its supporting tissues, including bones, cartilage, ligaments and joints. Together, these form the skeleton. The skeleton gives the body support and shape, and protects the internal organs.

Bones

Bones are strong structures that act as the framework for the skeleton. They play a crucial role in protecting the internal organs.

Bones have a dense outer layer called compact bone (also known as cortical bone) and a lighter, porous inner layer called spongy bone (also known as cancellous or trebacular bone). Both compact and spongy bone are mostly made of a mineral called hypoxyapatite, which is a form of calcium phosphate. This makes up around \(70\%\) of bone; the remaining \(30\%\) is a mix of cells and water.

Transcript

Inside the bone

A diagram of the end of a bone. Where the bone has been cut, there is red bone marrow. Extending through the core of the bone are blood vessels. The outer layer of bone is labelled "Compact bone" which is dense. The inner area of bone is labelled "Spongy bone", which is porous, as shown by the tiny holes throughout the structure.

The spaces in the spongy bone are where bone marrow is found. Red marrow makes blood cells. Yellow marrow stores fat.

Blood vessels run through the compact and spongy bone, playing an important role in bone development, repair and maintenance.

The outer surface of the bone is covered in a thin membrane called the periosteum (“peri” meaning “around” and “osteon” meaning “bone”). It has blood vessels and nerves that help the bone grow and heal.

The overall structure of bone gives it strength, but also flexibility and the ability to absorb shock.

The image shows some of the key bones in the skeletal system.

Transcript

Bones in the skeletal system

A diagram of a labelled skeleton.

• The head of the skeleton, or "Skull", is labelled. It consists of the top part labelled "Cranium" and the jaw, labelled "Mandible".
• The "Spinal column" extends from the head down to the pelvis. It consists of the "Cervical vertebrae", which is the neck portion, the "Thoracic vertebrae", which starts at the shoulders and extends down to the bottom of the ribs, the "Lumbar region", which is the lower back, and the "Sacrum" and "Coccyx" which are located in the pelvis.
• The collarbone is labelled "Clavicle". It connects the body to the arms.
• The "Scapula" is the shoulder blade.
• The "Sternum" is the breastplate from which the ribs extend.
• The "Ribs" are curved bones that surround the core of the body.
• The "Humerus" is the bone in the arm between the shoulder and the forearm.
• The forearm is made up of the "Ulna" and "Radius", which are the bones on the outside and inside of the arm, respectively.
• The "Carpals" are the bones in the wrist. The "Metacarpals" are the bones in the hand. The "Phalanges" are the bones in the fingers.
• The "Pelvic girdle" is the main pelvic bone.
• The "Femur" is the thigh bone.
• The "Patella" is the kneecap.
• The "Tibia" is the larger bone in the lower leg and the "Fibula" is the smaller bone.
• The "Tarsals" are the bones in the ankles. The "Metatarsals" are the bones in the foot. The "Phalanges" are the bones in the toes.

Cartilage

Cartilage is a flexible type of tissue that cushions the joints and reduces friction between bones so you can move easily. You typically find cartilage covering the surfaces of bones at your joints. It also covers structures like the nose, ears and parts of the rib cage.

Cartilage is made of cells called chondrocytes (“chrondro” meaning “cartilage” and “cyte” meaning “cells”). These produce a gel-like substance that is both strong and flexible.

Unlike bone, the cartilage does not contain blood vessels. It gets nutrients from surrounding tissues. This means that when cartilage is damaged, it takes a lot longer to heal.

There are three main types of cartilage:

• hyaline cartilage which provides smooth surfaces for joint movement, like between the ribs
• elastic cartilage which allows for flexibility, like in the ear
• fibrocartilage which provides strong support and absorbs shock, like in the spine.

Ligaments

Bones are connected at joints by strong bands of tissue called ligaments. They provide stability by holding the bones together and allowing you to move in a controlled way, while also stopping you from making overextended or abnormal movements that could injure you.

Ligaments are made up of dense, fibrous connective tissue. This gives them strength and flexibility. They support movement and keep your joints aligned.

Joints

The joints connect bones to let us move. They are complex structures containing various tissue types. Joints include cartilage and ligaments.

We can classify joints based on their structure and the material that holds the bones together. There are three primary categories:

• fibrous joints connect the bones with dense fibrous connective tissue. Most fibrous joints are immovable.
• cartilaginous joints connect bones with cartilage. Most cartilaginous joints allow for slight movement.
• synovial joints are characterised by a joint cavity containing synovial fluid, a slippery substance that reduces friction and helps the joint to move smoothly. All synovial joints can move freely.

Synovial joints are the most common and familiar joints in the body. There are different types of synovial joints, which we have summarised in the following table.

Joint images by OpenStax, licensed under CC BY 4.0.

 

Summary

The components of the skeletal system and their functions are outlined in the table.

Exercise

See how well you understand the components and function of the skeletal system with a quick quiz.

Data drill

Read the scenario and use the information provided to answer the questions in the quiz.

Dr. Pom Pompurin, a nutrition researcher, conducted a six-month study to examine the impact of calcium intake on bone health. He tracked the average weekly calcium intake of six healthy adults and assessed their bone health scores at the beginning and end of the study.

The bone health score, measured on a scale from 0 to 100, reflects changes in bone density and strength. The data is shown in the table.

Images on this page by RMIT, licensed under CC BY-NC 4.0