The human body: Week four
This page has been specially written for thousands of pupils from across Northern Ireland who are doing the Belfast Telegraph cross-curricular project themed on the human body. Over a six week period, we will look at systems in the human body. This week we will focus on the skeletal and muscular system – one of the most important systems in the body.
Skeletal and muscular system
The human skeletal system has six major functions including the production of blood cells for support, for movement, for protection and for growth.
Inside the body, hundreds of bones link together like scaffolding to form the skeleton. Without a skeleton, the body would collapse.
The skeleton holds the body rigid and gives shape to all the softer parts. It also protects the organs — the skull surrounds the brain, and the ribs act like a protective cages around the lungs and heart.
The skeleton is also an anchor for the muscles, which move the different parts of the body.
Bone is made of living cells surrounded by a framework of mineral, particularly calcium and phosphate, and a strong, elastic substance called collagen.
Humans and other mammals, fish, birds and reptiles all have an inner skeleton or endoskeleton, made of many separate bones.
The central part of the skeleton is the spine (vertebral column or backbone).
The spinal joints can move only a little, but the spine as a whole is very flexible.
Some creatures such as worms have no bones. Instead the pressure of fluid inside their bodies helps them keep their shape.
They are said to have a hydrostatic skeleton.
Insects, spiders and crabs have a hard casing or shell, called an exoskeleton. This kind of skeleton cannot grow larger.
As the animal grows, it has to shed its old skeleton, and a new, bigger skeleton hardens beneath.
Bones are linked together at joints
There are several types of joints, including fixed, hinge and ball-and-socket joints.
Fixed joints, such as those between the separate bones in the skull, cannot move.
Hinge joints, such as those in the elbow/knee, allow movement in one direction, like the opening and closing of a door, with no rotation (turning).
Ball-and-socket joints, such as the hip/shoulder, allow the bones to swing in two directions and also to twist.
If two bones just moved against each other, they would eventually wear away. To stop this happening, the ends of the bones in a joint are covered with a tough, smooth substance called cartilage. This is kept slippery by fluid in the body.
Living bone is tough and slightly flexible — only dead bone is white and brittle. Blood vessels pass through small holes in the bone’s surface and carry a steady supply of blood to the bone.
Some bones contain a jelly like substance called bone marrow which makes blood cells.
In a newborn baby, many of the bones are made of a soft, rubbery substance called cartilage. As a baby grows, the cartilage gradually turns into hard bone.
Our wrists and ankles are among the last to become bone. In later life, bones gradually become more fragile and brittle, and therefore break more easily.
Muscles and how they work
A simple movement such as lifting your arm involves dozens of muscles acting together in sequence with split second timing.
About 650 muscles are in the human body and are responsible for moving the various parts of the skeleton.
Muscles work in pairs. The largest muscle is called the gluteus maximus, in the buttock. The smallest muscles are the tiny muscles of the small bones inside the ear.
Altogether, muscles make up more than half of an adult’s body weight.
BICEPS AND TRICEPS MUSCLES
Muscles can pull, but they cannot push.
Many, such as the biceps and triceps muscles in the upper arm, are arranged in opposing pairs.
Muscles work by getting shorter, this means they contract. Muscles are attached to bones by strong tendons.
When the forearm is raised, the biceps contract and the triceps relax.
However, when the forearm is then lowered, the biceps relax and the triceps contract.
All muscles must be used regularly, or they waste away.
Regular exercise is an important part of staying healthy.
Taking part in a sport, or exercising two or three times a week, helps keep a person healthy.
Name: Amaya Ruth Preston
Tandragee Primary School
How tall are you?
What colour of eyes do you have? Blue/grey coloured eyes.
What exercise do you enjoy to keep your body healthy? I like to participate in hockey lessons. I play for a local hockey team and enjoy playing as part of a team. I also like to play netball in an afterschool club in school.
Which healthy foods do you enjoy eating? I really enjoy eating lots of fruit. My favourites are apples and bananas.
What is your top tip for healthy living? My top tip would be to get involved with lots of activities in school and also join a sports team in your local area. I think this is a great idea because even if you can't eat your 5 a day, you can still remain active and keep healthy.