Understanding the Human Locomotor System

The Locomotor System

The locomotor system is made up of the skeletal system and the muscular system.

The Skeletal System

The skeletal system is formed by bones and joints.

Purpose of the Skeletal System

• To serve as an internal framework for our bodies.
• To protect organs and internal tissues.
• To provide anchorage support for muscles.
• To manufacture blood cells.
• To serve as a reserve store of calcium and phosphorus.

Bones

Bones are organs composed of compact bone tissue on the outside and spongy bone tissue at the core. To avoid friction, the ends of our bones are covered with cartilage. The holes in the spongy bone tissue are filled with bone marrow. There are two types: red bone marrow, in which blood cells are produced, and yellow bone marrow, which is made up of adipose tissue.

Bones are hard because they contain calcium mineral salts.

Bones are classified by their shape:

• Long bones: e.g., the femur.
• Short bones: e.g., the vertebrae and wrist bones.
• Flat bones: e.g., the bones that make up the skull.

Joints

Joints are the places at which bones connect. There are three types:

• Fixed joints: Do not permit any movement of the bones, as in the case of the bones that form the skull.
• Slightly movable joints: These enable a limited amount of movement, such as the vertebrae. These bones are connected by discs of cartilage and ligaments.
• Freely movable joints: Enable movement in all directions. The contact zones between these bones are covered in cartilage and a lubricating liquid called synovial fluid. In these joints, the bones are connected by ligaments.

The Muscular System

The Muscles of the Locomotor System

The muscles enable fast, voluntary movements. They are connected to bones by tendons.

The muscles of the locomotor system can be divided into three groups, depending on their shape:

• Fusiform muscles: Such as the biceps or the triceps. Their ends may be divided into 2, 3, or 4 branches, in which case they are called biceps, triceps, or quadriceps.
• Flat muscles: Such as the pectoral muscles.
• Circular muscles: Such as the orbicularis oris.

Muscle Contraction

A muscle is said to contract when it becomes thicker and shorter. This process is controlled by the nervous system. A number of different muscles must be coordinated at the same time.

Skeletal muscles generally work in antagonistic pairs: when one muscle contracts, the other relaxes. For example, the biceps and triceps: the former causes the arm to bend, while the latter causes it to straighten.