7. The Skeletal and Muscular Systems

        The skeletal system helps you to support your body, protect the organs inside and move connected to the muscles. We have 206 bones (a baby has 300).
        Joints (articulaciones) are the places where two or more bones are connected. There are 3 types of joints:
1.    Fixed: permit little or no movement. E.g. skull
2.    Semi-movable: permit a limited movement. E.g. the vertebrates.

3.    Movable: permit a lot of movement. Bones here are connected by ligaments (strong tissue) and protected by cartilage (so bones don't touch to protect them from friction). E.g. knees, wrists, ankles



The muscular system helps you to move contracting or relaxing. We have around 650 muscles in our body. There are 2 types of muscles:
1.    Smooth / involuntary muscles:         you can't control them. Examples: stomach, intestinal walls or the cardiac muscles /  myocardium / the heart.
2.    Skeletal / voluntary muscles: you control them. They are connected to bones by non-elastic tissues: tendons, so when a muscle moves, the bone moves to.

Muscles can be of different shapes:
·         Spindle-shaped muscles: like the biceps and the triceps in the upper arms. They are thick in the middle and thinner at the end.
·         Flat muscles: like in the diaphragm or forehead.
·         Triangular muscles: like the deltoid at the top of the arms.
·         Circular muscles: like around the mouth, the pupils or the bladder.