Skeletal System

• THe function os the skeleton is to support, protect, and move the body.
• There are 213 bones in an adult human.
• The axial skeleton comprises the skull, vertebrae, ribs, and the sternum.
• The rib cage consists of the sternum and 12 pairs of ribs. The top seven ribs are true ribs attached to the breastbone, the middle three are called false ribs as they are connected via cartilage, and the bottom two are floating ribs as they are attached to the spine.
• Vertebrae are held together by ligaments and muscles. Between each vertebra, there is a disc of cartilage. These discs prevent friction.
• The last nine vertebrae of the spine are fused to form the sacrum.
• The appendicular skeleton consists of the pectoral and pelvic girdles and leg and arm.
• In the pectoral girdle, there is the collarbone (clavicle) and shoulder blade (scapula.)
• The arm comprises of the radius, humerus, ulna, carpals (wrist), metacarpals (hand bones), and phalanges (finger bones).
• The pelvic girdle consists of the hip bones and the sacrum.
• The leg comprises the femur, patella, tibia, fibula, tarsals (ankles), metatarsals (feet bones), and phalanges (toe bones).
• Cartilage consists of a flexible fibrous protein called collagen. It lacks blood vessels and acts as a shock absorber.
• The shaft of the bone is called diaphysis. The head of the bone is called the epiphysis.
• A long bone contains a hollow centre region called the medullary cavity, containing yellow bone marrow that stores fat.
• The periosteum is a tough fibrous layer surrounding each bone.
• Compact bone gives it strength and flexibility. It is made of bone cells called osteoblast. It is found in the shaft of bones.
• Spongy bone is found in the epiphyses of bones. It contains red marrow which produces blood cells. It gives moderate strength to bones but makes them lighter. 
• Bone marrow is the soft tissue inside the medullary cavity and spongy bone that produces blood cells.
• A joint is where two or more bones meet.
• In immovable joints, the joints are fused e.g. skull.
• In slightly movable joints, he joints between vertebrae in the upper spine are slightly moveable.
• Freely moveable joints contain synovial fluid which acts as a lubricant for joints.
• Ligaments are strong, slightly elastic tissue that connect bones.
• Tendons are flexible inelastic fibers that connect bone to muscle.
• A synovial joint is a freely moveable joint comprised of synovial fluid and membrane and cartilage.
• Ball and socket joints allow movement in all directions e.g. shoulder and hip.
• Hinge joints allow movement in one direction only e.g. elbow and knee
• In gliding joints, bones slide over each other e.g. wrist, ankle, spine
• Skeletal muscle causes body movements and contracts quickly but tires easily.
• Cardiac muscle is found in the heart and does not tire easily.
• Smooth muscle is an involuntary muscle that contracts slowly and is slow to tire e.g. bladder and uterus.
• Antagonistic muscles are two muscles that have an opposite effect on each other. Muscles can ONLY pull.
• Biceps contract to raise the lower arm (tricep relaxes.) Tricept contracts to lower the lower arm (bicep relaxes.)
• The bicep is a flexor muscle (closes the joint) while the tricep is an extensor muscle (opens the joint)
• Arthritis is caused by the inflammation of joints. This is prevented by wearing protective clothing.
• The skeleton is originally made of cartilage and is replaced by bone. This is called ossification.
• Ossification is caused by osteoblasts, which produce collagen, which is then hardened by calcium and phosphate. The osteoblasts then become dormant and are called osteocytes.
• Osteoclasts are bone-digesting cells.
• Parathormone removes calcium from the bone so the level of calcium in the blood can be raised for muscles and nerves to work properly.
• Diagram of the arm:

  A) clavicle

  B) pectoral girdle

  C) scapula

  D) humerus

  E) radius

  F) ulna

  G) carpals and metacarpals