The Skeletal System

Overview and Functions

The skeletal system forms the structural framework of the human body. It is composed of bones, cartilage, ligaments, and joints, providing support, protection, and facilitating movement.

• Support: The skeleton provides a rigid framework that supports the body and maintains its shape.

• Protection: Bones protect vital organs (e.g., the skull protects the brain, the rib cage protects the heart and lungs).

• Movement: Bones act as levers and joints serve as fulcrums for muscle action.

• Mineral Storage: Bones store minerals such as calcium and phosphorus, which can be released into the bloodstream as needed.

• Hematopoiesis: The production of blood cells occurs in the red bone marrow.

• Energy Storage: Yellow bone marrow stores lipids, serving as an energy reserve.

Types of Bone Tissue

• Compact Bone: Dense and organized into structural units called osteons (Haversian systems). Provides strength and resistance to bending.

• Spongy Bone (Cancellous Bone): Composed of a 3D lattice of trabeculae, supporting bone marrow and reducing bone weight.

Major Components of the Skeleton

• Axial Skeleton: Consists of the skull, vertebral column, ribs, and sternum. Forms the central axis of the body.

• Appendicular Skeleton: Includes the bones of the arms and legs, as well as the pectoral (shoulder) and pelvic girdles that attach the limbs to the axial skeleton.

Bone Structure Nomenclature

Common Terms and Definitions

Understanding bone features is essential for identifying anatomical landmarks and attachment points for muscles and ligaments.

The Axial Skeleton

Skull

The skull is composed of cranial and facial bones, protecting the brain and supporting facial structures.

• Cranial Bones: Frontal, parietal, temporal, occipital, sphenoid, and ethmoid bones form the cranial cavity.

• Facial Bones: Maxilla, zygomatic, nasal, mandible, and others shape the face and provide attachment points for muscles.

• Key Landmarks: Foramen magnum (large opening for spinal cord), occipital condyles (articulate with the first cervical vertebra), mastoid process, mandibular symphysis, and various foramina for nerves and blood vessels.

Vertebral Column

The vertebral column (spine) supports the body, protects the spinal cord, and allows flexible movement.

• Cervical Vertebrae (7): Smallest, support the head, allow for rotation and nodding.

• Thoracic Vertebrae (12): Articulate with ribs, have longer spinous processes.

• Lumbar Vertebrae (5): Largest, support the lower back.

• Sacrum: Five fused vertebrae forming the posterior wall of the pelvis.

• Coccyx: Four fused vertebrae forming the tailbone.

Intervertebral Discs: Pads of fibrocartilage between vertebrae, composed of an outer annulus fibrosus and an inner nucleus pulposus. They absorb shock and allow flexibility. Herniation of the nucleus pulposus can cause nerve compression.

Thoracic Cage

The thoracic cage protects the heart and lungs and supports the upper limbs.

• Ribs (12 pairs): True ribs (1-7) attach directly to the sternum; false ribs (8-12) attach indirectly or not at all; floating ribs (11-12) do not attach to the sternum.

• Sternum: Composed of the manubrium, body, and xiphoid process.

• Hyoid Bone: U-shaped bone in the neck that does not articulate with other bones; serves as an attachment for tongue and neck muscles.

Additional info:

• The appendicular skeleton, while not detailed in these notes, includes the pectoral and pelvic girdles and the bones of the limbs.

• Bone markings are critical for understanding muscle attachments, joint formation, and passage of nerves and vessels.