The Skeleton

Overview of the Human Skeleton

The human skeleton provides the structural framework for the body, supporting movement, protecting organs, and serving as a site for blood cell formation. It consists of bones, cartilage, joints (articulations), and ligaments.

• Bones: Rigid organs that form the skeleton and provide support and protection.

• Cartilage: Flexible connective tissue found in joints, rib cage, ear, nose, and other areas.

• Joints (Articulations): Locations where two or more bones meet, allowing for movement and flexibility.

• Ligaments: Bands of connective tissue that connect bones and stabilize joints.

The adult human skeleton is composed of 206 named bones, grouped into two main divisions:

• Axial skeleton (80 bones): Includes the skull, vertebral column, and thoracic cage.

• Appendicular skeleton (126 bones): Includes the upper and lower limbs, as well as the girdles that attach them to the axial skeleton.

Example: The femur (thigh bone) is part of the appendicular skeleton, while the vertebrae are part of the axial skeleton.

Axial Skeleton

Main Components of the Axial Skeleton

The axial skeleton forms the central axis of the body and is essential for protection and support.

• Skull: Protects the brain and forms the structure of the face.

• Vertebral column: Supports the trunk and protects the spinal cord.

• Thoracic cage: Composed of the ribs and sternum, protects the heart and lungs.

Example: The sternum is a flat bone located in the center of the chest, forming part of the thoracic cage.

The Vertebral Column

Structure and Function of the Vertebral Column

The vertebral column, or spine, is a flexible, segmented structure that supports the body and protects the spinal cord. In adults, it is formed from 26 bones.

• Transmits weight: Transfers the weight of the trunk to the lower limbs.

• Protection: Surrounds and protects the spinal cord.

• Attachment: Serves as attachment sites for muscles of the neck and back.

Example: The lumbar vertebrae are larger to support more weight from the upper body.

Regions and Normal Curvatures of the Vertebral Column

Major Regions of the Vertebral Column

The vertebral column is divided into five major regions, each with distinct characteristics and functions.

• Cervical vertebrae (7): Located in the neck region.

• Thoracic vertebrae (12): Located in the upper and mid-back, articulate with ribs.

• Lumbar vertebrae (5): Located in the lower back, support the most weight.

• Sacrum: Formed from five fused bones, inferior to lumbar vertebrae.

• Coccyx: Inferior to sacrum, commonly known as the tailbone.

Example: The sacrum forms the posterior wall of the pelvis.

Normal Curvatures of the Vertebral Column

Curvatures of the vertebral column increase its resilience and flexibility. There are two types of curvatures:

• Primary curvatures: Thoracic and sacral curvatures (convex posteriorly), present at birth.

• Secondary curvatures: Cervical and lumbar curvatures (concave posteriorly), develop as the baby begins to walk.

Example: The cervical curvature develops as infants start to lift their heads and crawl.

Summary Table: Regions of the Vertebral Column

Additional info: The curvatures of the spine help absorb shock and maintain balance during movement.