The Musculoskeletal System

Thanks to the musculoskeletal system we can move and stand straight. It supports and protects all organs. There are two musculoskeletal systems, the passive one and the active one. The passive one includes everything that does not move by itself, whereas the active one is everything that is directly involved in the moving process.

Bones

There are many types of bones in the body. Each one has a different role.

Here is a small overview:

• Long bones: The long bones, also called the tubular bones are bones that, as the names indicate, are elongated and tubular. They have a marrow cavity filled with yellow bone marrow. The ends of the bones contain plenty of spongiosa, the inner spongy bone substance. The bone marrow of the long bones produces blood. Examples of long bones: collarbone, forearm bone, toe bone, etc.
• Short Bones: Short bones tend to have a cube-like shape. Under a thin cortex, the layer of bone that surrounds the cancellous bone, there is only cancellous bone. Examples of short bones: Carpal and tarsal bones.
• Flat Bones: Flat bones are shallow, compact bones. Between two layers of cortical bone is a spongiosa, which has plenty of blood-forming bone marrow. Examples of flat bones are: the bones making up the skull, shoulder blades, sternum, etc.
• Irregular Bones: There are also irregular bones in our bodies. In most cases, the vortex and facial skull are classified as such, because they do not fit into any of the previous categories.

Muscles

Muscles are a vital part of the musculoskeletal system, as they make the whole movement happen. The 650 human muscles are made up of cells, just like each other part of the body. Each muscle is built differently and there are many types of muscle cells that cause movements through contracting. Muscles get their energy from ATP, the adenosine triphosphate.

Types of muscle cells:

• Skeletal Muscle Cells: The muscle tissues on the skeleton that initiate movements as they contract by being directly attached to two bones. These contractions are triggered by nerve cells that have special connections with muscle cells. The signal coming from the brain triggers the release of messenger substances, which then go into the muscle cells and "order" the sarcoplasmic reticulum (special ER of the muscles) to release calcium ions, which ultimately activate the myocyte, triggering the contraction.
• Cardiac muscle cells: They make up the muscular layer in the heart and they ensure that our heart beats rhythmically all the time. The heart muscles are very close together, because they have to distribute nerve signals quickly.
• Smooth Muscle Cells: Smooth muscle cells are spindle-shaped cells while the others are cylindrical. The smooth muscles work independently without being controlled by the brain. Their contractions are controlled by the autonomic nervous system. Smooth muscles are found on the walls of hollow organs, such as the intestines. They ensure the contractions of these organs, for example they help with digestion in the intestine.

Joints

Joints are the connection points between the bony and cartilaginous parts of the skeleton and enable movements. Depending on their structure, they are divided into groups: synarthroses, the artificial joints, diarthroses, the real joints and an intermediate form, the amphiarthrosis.

Synarthrosis: Tight connections between two bones due to connective tissue adhesions (e.g. skull bones), cartilage connections (e.g. ribs and breastbone) or ossification (e.g. sacrum).

Diarthroses: Real joints, two freely moving bones meet within a joint cavity. There they are separated by a narrow joint space. The entire joint cavity is surrounded by the joint capsule. The bones involved are the condyle and the socket. Both are covered with cartilage on their articular surfaces. This cartilage creates a smooth surface that allows for friction-free movement. There is also a liquid helping. Example: knee joint.

Amphiarthrosis: An intermediate form of diarthrosis and synarthroses, it allows minimal movements. Example: bones of the pelvis.