Joints - Anatomy

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Joints - Anatomy
Joints - Anatomy
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Video: The 6 Types of Joints - Human Anatomy for Artists 2023, February
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The joints

Joints are the mobile connection points between two or more bones and enable targeted movement. There are over 100 such joints in the human body. Their main task is to cushion and dampen pressure effects such as shocks and tensile forces…

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This is how a joint is constructed

A distinction is made between real joints (diarthroses) and false joints (synarthroses). Real joints have a joint space between the cartilage and the joint surface, which enables the joint to move more widely. Examples of real joints are, for example, the hip, ankle and knee joints.

Fake joints have limited mobility. They are important as growth zones in the body, after growth they can ossify. Examples of fake joints are, for example, parts of the skull bone, the sternum, between the ulna and the radius of the forearm.

A (real) joint consists of the following units:

  • Joint surface with a cartilage coating: The joint surfaces of the bones are coated with a smooth layer of cartilage so that the bones do not rub against each other. The cartilage ensures the necessary pressure distribution on the underlying bone. This is particularly important for joints that are subject to heavy weight, such as the knee or hip joint.
  • Joint gap: In real joints, the joint surfaces are separated from each other by an extremely thin gap.
  • Joint capsule: It closes the joint airtight from the outside and forms the joint cavity. The joint capsule consists of an inner and an outer layer. The inner layer has blood vessels and nerves, which also leads, for example, to the transmission of the information "pain" in the joint. The outer layer consists of strong fiber fabric. If a joint has to be immobilized for longer, these fibers can shorten. The result is limited mobility. In order to restore the mobility in the joint, for example physiotherapy (physiotherapy) helps.
  • Ligaments (ligaments): They are, to a certain extent, stretchable strands of connective tissue with collagen fibers. They specify the possible range of motion of a joint and stabilize it. If a band is overused, it can tear or tear completely.
  • Other structures: In some joints, there are other structures in the joint cavity, such as the meniscus (intermediate discs made of cartilage) and the cruciate ligaments in the knee. Other joints have a special shape such as the hip joint. Here the hip socket almost completely surrounds the head of the femur.

The "synovial fluid"

Joints work essentially like hinges, which should be well "lubricated" to function properly. The synovial fluid fulfills this requirement. It is produced by the cells of the synovial membrane, ensures the smooth functioning of the joint and acts as a shock absorber through the distribution of pressure. The synovial fluid is a highly viscous liquid, it is rich in hyaluronic acid and similar in composition to the blood serum.

Since the cartilage tissue in the joint has no blood vessels, it depends on an external supply of nutrients. The synovial fluid is also responsible for this - it nourishes the cartilage. When joints are moved, the exchange of nutrients between the synovial membrane and cartilage can take place better. Movement therefore ensures a better exchange of substances in the joints.

The range of motion of a joint

The directions in which a joint can move depends on the one hand on the shape of the joint surfaces. But muscles or ligaments also dictate the direction in which a joint can move. In addition, the range of motion of a joint is limited by muscles, soft tissues, ligaments or bones, for example the knee joint can no longer be bent from a certain position because the rear surface of the thigh and the calf touch.

The leg can only be stretched backwards to a certain point in the hip because a tight band in the groin stops movement. How agile you are depends on the individual. Stretching exercises can improve the mobility of some joints.

Source: Gesundheitsinformation.de: How do joints work?

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