We all know we have a skeleton, but what is bone and why do we need it?
- Bone is used for: Support, Protection, Leverage and as a Chemical storehouse
- Bone is made up of two components: Organic (collagen) and Inorganic (calcium phosphate)
- Bone formation involves three cells: Osteoblasts (bone forming) which produce the basic materials and proto-collagen upon which minerals are deposited, Osteocysts which are mineralised osteoblast on it's way to becoming bone and Osteoclasts (bone removal) which are cells that absorb bone by resorbing it.
- This formation and removal processes allow bones to maintain or change their shape or size during growth: modelling - bone sculpting during growth and remodelling - continuous removal and replacement of bone through life. This can be from functional adaptation and wear and tear during life.
Bone development
- Bone starts out as an ossified centre (where mineralisation of organic matrix begins)
- These form the diaphysis ie. the shaft of bones such as the tibia or humerus
- Secondary ossified centres also occur, which form the epiphyses, such as the ends of long bones
- A cartilage growth plate separates these two, and deposits bone and continues to make cartilage, making the bones grow longer.
- So basically, bone starts off small and continues to grow by gradual formation as bone is continually deposited!
Anatomy of bone at the macro-level
The Human Skeleton- Compact or cortical bone is dense and solid, but at the macro level, it is porous due to the penetration of many tiny blood vessels that carry nutrients into bone.
- The inner surface of bone is filled with cancellous, which saves weight, bone mass and makes it flexible rather than brittle! This cancellous bone is formed from trabeculae with collagen filling in the spaces.
- Each bone is covered with a layer called the periosteum, with the endoseum on the inside. These layers are made up of collagen with fibres that enter the bone.
- Nutrient arteries enter the bone through nutrient foramen, which supplies the marrow cavities with blood. Some bones have a larger supply of blood going through them, depending on where they are situated in the skeleton. For instance, the femur has a major blood supply through it. In an archaeological sense, if this bone was broken, the individual would have bleed to death as it would not have been possible to stop the flow of blood.
206 bones form the adult skeleton and 300 - 350 form an infants skeleton at birth.
- Skull: 28 (8 Cranial, 14 Facial and 6 Ear Bones)
- Vertebra: 26 (7 Cervical or neck, 12 Thoracic or back and 5 Lumbar or lower back.
- Ribs: 24 (Plus the sternum or breast bone, 2 scapula or shoulder blades and 2 clavicles or collar bones)
- Pelvic Girdle: Pelvis is formed of three fused bones called the Os Coxae: Pubis, Illium and Ischium
Coccyx or vestigial tail (3-5 variably fused segments)
- Arms: 3 bones in each side (Humerus, Radius and Ulna)
- Hand: 27 in each side
5 Metacarpals
14 Phalanges (5 Proximal, 4 Intermediate and 5 Distal)
- Legs: 4 bones in each side (Femur, Tibia, Fibula and patella)
- Foot: 7 Tarsals (Talus, Calcsneum, Cuboid, Navicular, and Medial, Intermediate and Lateral Cuneiform)
14 Phalanges
