To support or hold in shape many living organisms have a skeletal system. Organisms may have An exoskeleton – skeleton on the outside of the body eg. Insects Endoskeletons – skeletons on the inside of the body eg. Humans The human skeleton is made of bones that meet each other to form joints, covered on each end by cartilage and are moved by the contraction and relaxation of muscles

The skeletal system serves five main functions: Support Movement Protection Making red and white blood cells Storage of some minerals

Bone is made of: Bone is Mostly mineral substances such as calcium phosphate and small amounts of magnesium salts And Collagen fibres (gives it elasticity). Collagen is a protein Alive Needs to be supplied with food and oxygen Have different layers: Compact bone – on the outside Spongy bone – layer underneath that has spaces in it to keep the bone from being too heavy Bone marrow – in the centre, has a good blood supply and is very soft, red and white blood cells and platelets are made here

Joints Cartilage Is much softer than bone Allows bones to move easily over each other Found at the end of bones Contains collagen There are different kinds of joints: Fibrous joints – joins bones by fibres such as in the skull. These are called Sutures Synovial Joints – found when two bones need to move freely. The bones are held together by ligaments. Eg. Elbow or shoulder. There are two types of Synovial Joints Hinge joints – such as the elbow work like a door on a hinge. Allows up and down movement or side to side Ball and socket joints – such as the shoulder and hip. A ball end fits into a socket in the other. Allows circular movement

There are three kinds of muscle: Cardiac Muscle (C ) – found only in the heart Smooth muscle (Sm) -also called involuntary muscle since we do not control them consciously. It is found in organs such as bladder and alimentary canal Striated muscle (St) – attached to bones to make bones move by contraction (the muscle gets shorter) or relaxation (the muscle gets longer). These are also called voluntary muscles because we control them Tendons are collagen fibres that join muscles to bones Tendons do not stretch but they are very strong