What is the structure of a skeleton?

Skeletal System:

Bones:

- Rigid organs that provide support, protection, and movement.

- Composed of specialized cells, extracellular matrix, and minerals (calcium, phosphorus).

Bone Structure:

1. Compact Bone:

- Dense, hard outer layer that provides strength.

- Osteons (cylindrical structural units) contain Haversian canals (for blood vessels).

2. Cancellous Bone:

- Spongy, porous inner bone.

- Contains bone marrow (produces blood cells).

Types of Bones:

1. Long Bones:

- Predominantly long, cylindrical (e.g., thigh bone, arm bone).

- Composed mostly of compact bone.

2. Short Bones:

- Approximately cube-shaped (e.g., wrist, ankle bones).

- More cancellous bone than compact bone.

3. Flat Bones:

- Thin, broad (e.g., skull, ribs, shoulder blades).

- Composed of two layers of compact bone with cancellous bone in between.

4. Irregular Bones:

- Complex shape, don't fit other categories (e.g., vertebrae, hip bone).

Bone Markings:

- Surface features that serve specific functions:

1. Joint surfaces (smooth for articulation)

2. Muscle attachments (ridges, crests, processes)

3. Tendon attachments (tubercles, trochanters)

4. Ligament attachments (grooves, notches)

5. Nutrient foramina (for blood vessel entry)

Joints:

- Sites where bones meet. Classified based on structure and movement:

1. Fibrous Joints:

- Bones directly connected by fibrous tissue. Limited to no movement.

- Examples: Skull sutures.

2. Cartilaginous Joints:

- Bones connected by cartilage. Limited movement.

- Examples: Intervertebral joints.

3. Synovial Joints:

- Freely movable joints with a joint cavity filled with synovial fluid.

- Most common joint type.

- Features include joint capsule, synovial membrane, and articular cartilage.

Major Skeletal Structures:

1. Axial Skeleton:

- Bones of the head, neck, and trunk. Includes skull, spine (vertebrae), and rib cage.

2. Appendicular Skeleton:

- Bones of the limbs and their attachments. Includes shoulder girdle, upper limbs, pelvic girdle, and lower limbs.

3. Vertebral Column:

- Stack of vertebrae that forms the spine. Functions in support, protection, and movement.

Functions of the Skeleton:

- Support: Provides a framework for the body.

- Protection: Protects vital organs (e.g., brain in skull, lungs in ribcage).

- Movement: Facilitates movement through skeletal muscles attached to bones.

- Storage: Bone marrow stores minerals, produces red and white blood cells.

- Blood production: Red and white blood cells are produced in the bone marrow.

- Mineral storage: Bones act as reservoirs for calcium, phosphorus, and other minerals.

- Heat production: Skeletal muscle contractions generate body heat, helping maintain body temperature.

The skeleton works in conjunction with the muscular system to enable movement, support, and protection while providing a mineral reserve for the body.