Structure of the Human Skeleton
- Function of the human skeleton: support, structure, protection.
- The human skeleton is made mostly of bone, with cartilage covering the end of moveable joints to provide lubrication, so it is easier to move.
- As a foetus develops, the skeleton is made only of cartilage.
- During growth and development, this is mostly replaced by bone. This process is ossification.
- Bone and cartilage are living tissues – they contain living cells.
- They require nutrients and oxygen, which are supplied by the blood.
- Compact bones are found in most of the long shafts of bone in the body, i.e. the limbs.
- Compact bone has many closely packed concentric circular arrangements.
- Each circle is called a Haversian system.
- The lacunae, which can be seen above, and the ‘thread-like’ canaliculi which branch from them are filled with osteocytes (which begin their lives as bone forming cells called osteoblasts).
- These cells synthesise and secret the fibrous protein tropocollagen outside their plasma membranes.
- Tropocollagen molecules link together end-to-end and side-to-side to form collagen fibres.
- An inorganic mineral containing calcium phosphate is deposited amongst these fibres.
- The mineral also contains magnesium and carbonate.
- Cells become completely surrounded by and trapped within a matrix collagen and calcium phosphate.
- Collagen gives the bone tensile strength since collagen fibres are very strong, whereas calcium phosphate gives rigidity and compressive strength.
- This is important in leg bones - they carry the weight of the body.
- Living bone is broken down by osteoclasts, allowing bone structure to be altered, for example to repair damage.
- Hyaline cartilage is a translucent tissue found covering the ends of bones at moveable joints, in the ribs where they join to the sternum, and in the C-shaped cartilage rings that surround and support the trachea.
- The living cells in cartilage are called chondrocytes, they produce and maintain the matrix in which they lie.
- Being protein secreting cells, they have a well developed Golgi apparatus and endoplasmic reticulum.
- Unlike bone, the matrix does not contain calcium phosphate or blood vessels.
- The chondrocytes gain nutrients by diffusion from surrounding tissue fluids.
- The matrix consists of water, collagen and glycoproteins.
- The surface of the hyaline cartilage at joints is very smooth and slippery.
- Fine collagen fibres are closely packed and arranged parallel to the surface.
- This is then covered by a very smooth, glycoprotein layer, making it slippery to prevent bones from wearing.
Axial and Appendicular Skeleton
- The human skeleton consists of the axial skeleton and the appendicular skeleton.
- The axial skeleton comprises of the middle of the skeleton - the skull, vertebral column, ribs and sternum.
- The appendicular skeleton comprises of the limb bones, the pectoral girdle.
The Axial Skeleton
- There are 33 vertebrae, 7 cervical (support head/neck), 12 thoracic (support chest/rib articulation), 5 lumbar (large muscles of lower back attach to), 5 fused sacral vertebrae (supports and articulates with hip bones), and the 4 fused tail vertebrae - the coccyx.
- Joints between vertebrae are known as intervertebral joints.
- Each vertebra is joined to the next by ligaments.
- Between each vertebra there are disks of cartilage, intervertebral disks, which act as shock absorbers
- Lumbar consists of
- Centrum: Load-bearing part.
- Neural Arch: Holds neural canal - spinal column.
- Transverse processes: Project outwards/sideways - powerful lower back muscles attach here, requiring the transverse process.
- Neural spine - Backwards pointing process, larger than in thoracic vertbrae.
- Articular processes - On the upper and lower surface, in contact with the vertebrae either side.
- Thoracic vertebrae are similar, except the neural spines are much longer and more slanted than in a lumbar vertebra.
The Appendicular Skeleton
- In each limb there is a similar basic structure - a single bone which articulates with the girdle, then two bones in the lower limb.
- Numerous small bones make up the wrist and ankle, hand and foot.
- In both hand and foot there are 5 digits- this is known as a pentadactyle limb.
That's the end of the topic!
Drafted by Bonnie (Biology)