This is how skeletons and joints work

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Last Medical Review: March 31, 2020
Medically Reviewed by Dr. Elisabeth Vincent Hamelin
Muscles (March 31, 2020)
Skeleton (March 31, 2020)

The skeleton has several important tasks. It keeps us upright, protects our internal organs and attaches to the muscles. The bones of the skeleton are held together by joints. In the joints the legs can move towards each other. It allows the entire body to move. The skeleton also forms the blood cells.

In this text you can read about how the skeleton and joints are constructed and how they work in different parts of the body.

So the skeleton is built up

The human skeleton is made up of 206 bones. Some bones are large, such as the femur and hip. Other bones are very small, like the auditory bones.

There are different types of bones

There are different types of bone in the skeleton:

  • Tubular bones are the long and narrow skeletal parts found in the arms and legs. Large tubular bones are hollow.
  • Short legs and legs with irregular shapes are found in wrists and ankles, among other things. The vertebral vertebrae are also included in this type.
  • Flat legs are in the skull. The sternum, ribs, shoulder blades and hip bones also count as flat bones.

The bone of the skeleton consists of bone tissue

The skeleton is made up of bone tissue. There are two types of bone tissue:

  • Compact bone tissue is compact and heavy and contains blood vessels, nerves and lymphatic vessels.
  • Fungal bone tissue is lighter and contains cavities and bone marrow.

Each bone contains both compact and spongy bone tissue. This makes the skeleton strong, but still not too heavy.

Inside the legs are bone marrow

The bone marrow is found in the fungal bone tissue and in the marrow. The marrow is a cavity at the bottom of the leg. The bone marrow can be both red and yellow. In the red bone marrow, red and white blood cells are formed. The yellow bone marrow contains largely fat.
In the spongy part of the bone there is red bone marrow in both adults and children. In the marrow, the bone marrow is red in children, but the more yellow you get the older you get.

On the surface of the legs is the retina

Each bone is surrounded by a thin membrane called the retina. In the retina there are blood vessels that carry oxygen and nutrition to the bone. Nerves also have nerves. Therefore, the bone membrane is very sensitive to pain.

This is how the joints work

In one joint, two or more bones meet. The surfaces of the bones that meet in the joint are called joint surfaces. Often, one leg joint surface is rounded while the other leg joint surface is shaped like a pit.

Cartilage is on the joint surface. The cartilage provides stability and protects different parts of the body. The cartilage in the joints is hard and slippery and prevents the surface of the bone from being torn or damaged. The cartilage also allows the bone’s surfaces to slide easily against each other.

Synovial fluid

Between the joint surfaces there is a narrow space with joint fluid. The joint fluid makes it easier for the legs to slide against each other. The joint fluid also adds oxygen and nutrients to the joint cartilage.

Joint capsule and ligaments

The joint is surrounded by the joint capsule. The capsule sits around the entire joint and holds the joint fluid in place. On the outside of the trail there are also ligaments. The ligaments hold the joint together and prevent the legs from moving in the wrong direction. The muscles that sit around the joint also help hold the joint together.

Different types of leads

The joints can look different and they can work in different ways:

  • Hinge joints can be moved back and forth, or bent and stretched. The elbow joint and the joints of the fingers and toes are examples of hinged joints.
  • Rotary joints are less common, but are found, for example, between the jet leg and the elbow bone in the forearm. In a pivot joint, the leg ends can only be rotated in relation to each other.
  • Two-axis joints can be moved in several ways. For example, the wrist can be bent forwards, backwards and sideways. The base of the thumb can also be moved in two planes.
  • Ball joints can be moved in all directions. The end of one leg of the joint is rounded in ball joints. The hip joint and the shoulder joint are examples of ball joints.
  • Planes can only move a little by sliding on each other. The counters in the spine are flat joints.


The skull consists of the so-called brain dish and the facial skeleton. The skull consists of twenty-nine legs. The brain bowl is made up of the forehead bone, two head bones, two temporal bones, the wedge bone, the sieve bone and the neck bone. These bones protect the brain.

The jaw joint is the only joint of the skull. The other bones in the skull are joined by so-called joints. The joint consists of connective tissue and cartilage tissue or bone tissue.

The facial skeleton protects the eyes, oral cavity and nasal cavity. The facial skeleton includes, for example, the lower jawbone and upper jawbone, nasal bone and oxbone.

The spine

The spine is made up of the following legs:

  • Seven neck vertebrae
  • twelve thoracic vertebrae
  • five lumbar vertebrae
  • the cruciate bone, which consists of five intersected cross vertebrae
  • four tail vertebrae.

In each vertebra there is a hole. Since the vertebrae are stacked on top of each other, a channel is formed through the holes. In the canal are the spinal cord. The vertebrae are held together by ligaments and muscles making the spine flexible and firm.

Disks and facet joints hold together the vertebrae

The vertebrae are connected to each other through two types of joints:

  • The counters contain cartilage. They cushion bumps and facilitate spinal movements. The disks are located between the vertebrae of the spine. They are joints of the type joints.
  • The facet joints are small joints that sit on the back of the spine.

On the vertebrae there are various committees called thorns and transverse projections. The ligaments and muscles are attached to the projections. It makes the spine stable. There are short ligaments between the vertebrae. The longest ligaments extend along the entire spine.


The neck is the upper part of the spine. The two top vertebrae and the neck bone together form the neck joint. The downside allows you to turn a lot on your head.

Shoulder, arm and hand

The shoulder joint is made up of the clavicle and the shoulder blade. The arm contains three large bones, the upper arm bone in the upper arm and the beam bone and the elbow bone in the forearm. The hand contains many small bones.

The shaft can be moved in three planes

The upper leg and shoulder blade are in contact with the shoulder joint. The shoulder joint is a ball joint and is the body’s most moving joint. The movements also occur in the joints of the clavicle. It allows you to raise your arm above your head.

The shoulder joint is surrounded by strong muscles that keep the joint stable. The shoulder joint’s joint cap and ligaments are more movable than other joints. Sometimes the legs that meet in the joint can slip out of position. It is called because the shaft goes out of joint.


In the elbow joint are the upper arm bone, the elbow bone and the ray bone. The joint is very stable because the joint surfaces fit well with each other. The ligaments in the elbow joint also contribute to its stability. The path between the upper arm and the elbow is a hinged joint. The path between the elbow bone and the beam bone is a pivot joint. There is a ball joint between the forearm bone and the ray bone. A joint capsule sits around the entire joint.


The wrist is the joint between the ray bone, the elbow bone and the palm of the hand. The Act of Law consists of eight small legs that are held together by strong ligaments. hHadlovs legs are arranged in two rows. The wrist can be moved forwards, backwards and can be rotated.

The joints of the fingers

The joints of the fingers are of the type hinged joints. You can only bend and stretch these joints. The trail that is at the bottom of the thumb is an exception. It is called saddle and can be moved in two planes. The joints are stabilized by strong ligaments.

The chest protects the heart and lungs

The chest consists of the twelve thoracic vertebrae, the sternum and twelve pairs of ribs. The bones of the chest protect, among other things, the heart and lungs. The chest also attaches muscles that are important for breathing.

The pelvis protects the intestines and bladder

The pelvis consists of the cruciferous bone and two hip bones. The bones together form a broad ring that protects, among other things, the bladder and parts of the intestine.

Hip bones

The hip bones are part of the pelvis. The hip bones are made up of three bones called bowel bones, sit bones and pubic bones. The bowel protects the intestines. At the front, the two hip bones are joined by a joint called the pubic joint. It is also called the symphysis. On each side at the back of the back there is a joint between the hip and the sacrum.

The hip joint

The hip joint is a ball joint, but it is not as mobile as the shoulder joint. This is partly because it is stabilized by the body’s strongest ligaments.

The joint surfaces are formed by the femoral head and a pit in the pelvis.

The leg and the foot

The skeletons in our bones are made up of the femur, kneecap bone, calf bone and tibia. The femur is the longest leg of the body. The tibia is included in the knee joint, while both the tibia and calf bone are included in the ankle joint.
The foot consists of the ankle, middle foot and toes. The legs in the foot are arranged as arches both longitudinally and transversely. This makes the walking softer and the load on the knees, hips and back decreases.

The knee joint

The knee joint is the largest joint of the body. The joints of the knee joint are formed by the lower part of the femur and the upper part of the tibia. In front of the knee joint is the kneecap bone which has a joint surface towards the knee joint. Around the joint surfaces of the knee and the kneecap is a capsule that holds the joint fluid in place.

The knee joint is a type of hinged joint. It can be stretched and bent. When the joint is bent, the ligaments are slightly relaxed, and the lower leg can also be slightly rotated in relation to the femur.

Between the joint surfaces of the knee are two cartilage discs, so-called meniscus. They make the joints better match each other. The meniscus can be damaged if you twist your knee sharply.

There are various ligaments to hold the joint together. The crossbands are tight ligaments that sit inside the knee. On the sides there are also ligaments that stabilize the joint.

The foot of the foot

The ankle joint actually consists of two joints. The paths are called the upper and lower bones. There are strong ligaments around both joints.

The upper fuselage joint includes the tibia, wad bone and the fuselage which is in the ankle. The ankle can be bent and stretched in this joint.

The lower leg of the leg is between the jump leg, heel leg and boat leg in the ankle. Here the ankle can be bent, stretched and twisted.

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