............................ THE LOCOMOTOR SYSTEM AND ITS DISEASES

Introduction. We all can move but not all of the organisms can do that. For example, plants die in the same place where they were born. This is very important, try to imagine how our lifes would look like if we weren't able to move. How would we get food? How would we escape from danger? Our ability to move is based on the contractile structures, the muscles, which are responsible for moving the rigid levers, the bones, but are the bones a living structures or are they made of the inert mineral matter? Why do many older people have pain related to their bones? This interesting chapter explains all of those things.

Activities to do. Read the explanations on the skeletal system and perform the first and the second Multiple Choice Test, the Relate Pictures with Names. Then read the text on the muscular system and perform the following exercises Multiple Choice Test, Relate Pictures with Names and the Crossword.

1 . The human locomotor system. Is the device that allows us to move and change places from one tho another (locomotion). It is constituted by the skeletal system and the muscular system.

2 . The skeletal system. Is responsible for supporting the body, protect vital organs, serve as an insertion to the muscles and prodce the blood cells. It is formed by a semi-rigid elements (cartilages), a rigid elements (bones) and flexible elements which allow the connection between the bones (ligaments) and between the bones and muscles (tendons).

3 . The cartilages. Are the semi-rigid structures of the cartilaginous tissue, which is a form of the connective tissue where in its inercellular subctance, the non fibrous substance predominates over the fibers. The unripe cells of the cartilaginous tissue are called chondroblasts and the mature - chondrocytes. An example of the cartilage is the pinna.

4 . The bones. Are the hard structures of the bone tissue, which is a tissue derived from the cartilaginous tissue, characterized by the fact that the intercellular substance presents a higher percentage in the weight of precipitation of the calcium phosphate (60%) and calcium carbonate (5%) than of the organic substance called osteon (30%), which is essentially formed by the fibers of the collagen protein. Its unripe cells are called the osteoblasts and the mature cells - the osteocytes. Moreover, It presents some cells called the osteoclasts which are responsible for destroying the bone tissue when it is necessary to reshape the bone. The osteocytes occupy a small elongated gaps that exist in the extracellular material of the calcareous nature, mentioned above. The bones have canals called the Haversian canals where pass the arteries, veins, nerves and lymphatic vessels, that keep the bone cells alive.

The stem (diaphysis) which is made of the compact bone tissue and the two ends (epiphysis) that are made of the spongy bone tissue are distinguished in the long bones.

Inside the diaphysis lays the yellow bone marrow (bone marrow) formed by cells filled with grease and in the empty spaces of the epiphysis lays the red marrow formed by stem cells of the red blood cells and white blood cells from the blood.

The contacts between bones are called joints. There can be three types of them:

Immovable. Are those that do not allow the mobility between the bones. For examples the joints between the bones of the skull, called sutures.

Semimovable. Are those that allow a certain mobility between the bones. For example the joints between the vertebrae, which present a cartilaginous intervertebral disc.

Movable. Are those that allow a high mobility between the bones, as it happens in the knee joint, where the whole knee is located inside a capsule of connective tissue filled with a absorbing fluid called synovial fluid.

5 . The ligaments. Are the structures of the connective tissue that connect the bones to each other.

6 . The tendons. Are the structures of the connective tissue that connect the muscles together or connect the muscles with the bones.

7. The human skeleton. Is constituted by 206 bones. Some form the axial skeleton (skull, vertebal column, ribs and sternum) and the rest form the appendicular skeleton (upper extremities, shoulder girdle, lower extremities and pelvic girdle).

8. The muscular system. Is the system that performs the movements thanks to the ability to contract with its cells, also known as muscular fibers. These are elongated, have several cores and contain many contractile myofibrils formed by proteins of actin and myosin. The muscle fibers join together and form musclar fascicles and these, in turn, come together and form the muscles. These are coated with a tissue called perimysium whose extension at the ends of the muscle forms the tendons which serve as an attachment to the bones.

Three types of muscle tissue can be differentiated:

• The striated muscle tissue. Is called that because when seen under the microscope has a striated appearance due to alternating fibers of actin and myosin. Is presents a voluntary contraction. It forms the muscles which take part in the process of the locomotion.
• The smooth muscle tissue. It presents an involuntary contraction. Constitutes the muscles that move the viscera such as the stomach, intestine, respiratory canals, etc.
• The cardiac muscle tissue. It presents a striated structure and an involuntary contraction. It is only in the heart.

9. The muscles of the human body. Can be differentiated into the ones of the head, of the neck, of the trunk, of the upper extremities (arm and forearm that is the part that goes from elbow to hand) and of the lower extremities (thigh and leg which is the part that goes from knee to foot).

Arthritis. The pain of the mobile joints due to the inflammation of the synovial membrane that secretes the synovial fluid. Sometimes it is caused by an infection.

Arthrosis. The pain of the joints due to a degeneration of articular cartilage because of the aging process.

Delayed onset muscle soreness. The pain of the muscles due to the accumulation of the lactic acid in the muscle fibers when they are required to make an effort to which they arenot accustomed.

Infantile rickets. The slow growth of the bones due to the lack of calcification as a result of the lack of the vitamin D in the diet.

Osteoporosis. The decrease in a bone mass due to a lack of extracellular matrix of the collagen on which calcium phosphate can accumulate. It is a natural process during aging. Can be compounded by hormonal changes such as those that occur during menopause.

Rheumatoid arthritis. The symmetrical chronic arthritis of an unknown origin or due to a mistaken immune response against itself's synovial membrane.

Sprain. The overstretch of a tendon due to a bad move.

11. The rules to prevent the disorders of the locomotor system. The main source of the locomotor system's problems comes from the spinal column. It is because the head is heavy and leans all day long on the spinal column and also, when we lift heavy things, for examle a suitcase, all the efford is taken by the spinal column. To avoid the back pain the following things should be considered:

• To sit right (see the two attached pictures) and if the computer is used to have the top of the screen on the height of the eyes.
• To lift heavy objects properly (see the attached picture) and to try not to carry much weight on a regular basis.
• To sleep on a mattress very consistent, that is not easily deformed.
• To do soft exercises regularly, such as walking or taking a bike instead of using a public transport, climbing stairs instead of taking the elevator, swimming, etc.. All this increase the muscular tone and helps the posture to be more like the student who is sitting frontal in the drawing. This can avoid current pains and those when the person is older.

Crossword (Spanish activity. Activity in English is under construction)