2. Skeleton and muscular system

Functions of the muscular system

The main function of the muscular system is to produce movement of the body. Depending on the axis and plane, there are several different types of movements that can be performed by the musculoskeletal system. Some of the most important ones include:

Flexion of leg (Flexio cruris); Image: Paul Kim

Flexion of legFlexio cruris1/8Synonyms: Flexion of knee, Flexio genus

  • Flexion and extension: movement of decreasing or increasing the angle between the bones involved in the movement, respectively. This motion takes place in the sagittal plane around a frontal axis. An example of flexion is bending the leg at the knee joint, whereas extension would be straightening knee from a flexed position.
  • Adduction and abduction: movements of bringing the parts of the body towards or away from the midline, respectively. These movements are carried out in the frontal plane around a sagittal axis. For example, abduction of the arm at the shoulder joint involves moving the arm away from the side of the body, while adduction involves bringing it back towards the body.
  • Rotation is the movement in which a part of the body rotates around its vertical (longitudinal) axis in the transverse plane. This movement is defined relative to the midline, where internal rotation involves rotating the segment towards to the midline, while external rotation involves moving it away from the midline. Examples include lateral or medial rotation of the thigh.
  • Supination and pronation are special types of rotatory movements usually used to describe the movements of the forearm. Supination is essentially a lateral rotation of the forearm which turns the palms anteriorly (if the arm is anatomical position) or superiorly, when the elbow is flexed. These movements are also sometimes used to describe movements in the ankle and foot, in which supination means rolling the foot outwards, while pronation means rolling the foot inwards.

Both during movement and stationary positions, muscles contribute to the overall support and stability of joints. Many muscles and their tendons pass over joints and thereby stabilize the articulating bones and hold them in position. In addition, the muscles also play an important role in maintaining posture. While the movements occur mainly due to muscles intermittently contracting and relaxing, the posture is maintained by a sustained tonic contraction of postural muscles. These muscles act against gravity and stabilize the body during standing or walking. The postural muscles include the muscles of the back and abdominal muscles.

Another important function of muscles is heat production. Muscle tissue is one of the most metabolically active tissues in the body, in which approximately 85 percent of the heat produced in the body is the result of muscle contraction. This makes the muscles essential for maintaining normal body temperature. 

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