The Axial and Appendicular Skeleton: Structure and Function

Axial and Appendicular Skeleton

Divisions of the Adult Skeleton

The human skeleton is divided into two major parts: the axial skeleton and the appendicular skeleton. Each division has distinct structural and functional roles in the body.

• Axial Skeleton (80 bones): Forms the vertical, central axis of the body and includes the skull, vertebral column, and thoracic cage.

• Appendicular Skeleton (126 bones): Comprises all bones of the upper and lower limbs, as well as the pectoral (shoulder) and pelvic girdles.

Components of the Axial Skeleton

The axial skeleton contains bones in the following regions:

• Head (skull-cranium): Includes cranial bones, facial bones, and ear ossicles.

• Neck and Back (vertebral column): Consists of vertebrae, sacrum, and coccyx.

• Chest (thoracic cage): Composed of the sternum and ribs.

Overview Diagram

The skeleton is visually divided into axial and appendicular regions. The axial skeleton includes the skull, vertebral column, and thoracic cage, while the appendicular skeleton includes the limbs and girdles. Additional info: The diagram typically labels major bones such as the clavicle, scapula, humerus, radius, ulna, pelvis, femur, tibia, and fibula.

The Skull (Cranium)

Structure of the Skull

The skull, or cranium, consists of 22 individual bones. Most are immoveable, except for the mandible (lower jaw), which is moveable.

• Immoveable bones: Form the majority of the skull and are joined by sutures.

• Moveable bone: The mandible, which allows for movement during chewing and speaking.

The cranium is made up of two sets of bones:

• Facial bones: Support the face.

• Brain case (cranial vault): Protects the brain.

Cranial Vault (Brain Case)

The cranial vault is the portion of the skull that encloses and protects the brain.

• Main function: Protection of the brain.

• Inner area: Known as the cranial cavity, which houses the brain.

• Superior portion: The calvaria (skullcap), which is the rounded upper part of the cranial cavity.

Key Terms and Definitions

• Axial skeleton: The central part of the skeleton, including the skull, vertebral column, and thoracic cage.

• Appendicular skeleton: The portion of the skeleton that includes the limbs and girdles.

• Cranial vault: The part of the skull that surrounds and protects the brain.

• Calvaria: The dome-like upper portion of the cranial vault.

• Mandible: The lower jawbone; the only moveable bone of the skull.

Example: Functional Importance

• The axial skeleton provides structural support and protection for vital organs such as the brain, spinal cord, heart, and lungs.

• The appendicular skeleton enables movement and interaction with the environment through the limbs.

Additional info:

• The adult human skeleton typically contains 206 bones in total.

• Sutures are fibrous joints that connect the bones of the skull, providing strength and stability.