Overview of the Human Skeletal System: Axial and Appendicular Divisions

Skeletal System

Main Divisions of the Human Skeleton

The human skeleton is divided into two major parts: the axial skeleton and the appendicular skeleton. Each division contains specific groups of bones that serve structural and functional roles in the body.

• Axial Skeleton: Forms the central axis of the body and includes the skull, vertebral column, and thoracic cage.

• Appendicular Skeleton: Comprises the limbs and girdles that attach them to the axial skeleton.

Axial Skeleton

The axial skeleton provides support and protection for the brain, spinal cord, and organs in the thorax. It consists of:

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

• Auditory Ossicles: Small bones in the middle ear involved in hearing.

• Hyoid Bone: Located in the neck, supports the tongue and aids in swallowing.

• Vertebral Column: Also known as the spine, it protects the spinal cord and supports the head and body.

• Thoracic Cage: Includes the ribs and sternum, protecting the heart and lungs.

Axial Skeleton Bone Count (from diagram)

Region	Number of Bones
Skull	22
Auditory Ossicles	6
Hyoid	1
Vertebral Column	26
Thoracic Cage	25

Appendicular Skeleton

The appendicular skeleton facilitates movement and interaction with the environment. It consists of:

• Pectoral Girdle: Attaches the upper limbs to the trunk (shoulder region).

• Upper Limbs: Includes the arms, forearms, wrists, and hands.

• Pelvic Girdle: Attaches the lower limbs to the trunk (hip region).

• Lower Limbs: Includes the thighs, legs, ankles, and feet.

Appendicular Skeleton Bone Count (from diagram)

Region	Number of Bones
Pectoral Girdle	4
Upper Limbs	60
Pelvic Girdle	2
Lower Limbs	60

Key Terms and Definitions

• Axial Skeleton: The part of the skeleton that includes the bones of the head and trunk.

• Appendicular Skeleton: The part of the skeleton that includes the bones of the limbs and girdles.

• Vertebral Column: A series of vertebrae extending from the skull to the lower back, protecting the spinal cord.

• Thoracic Cage: The rib cage and sternum, protecting vital organs in the chest.

• Pectoral Girdle: The set of bones connecting the arms to the axial skeleton.

• Pelvic Girdle: The set of bones connecting the legs to the axial skeleton.

Examples and Applications

• Clinical Application: Fractures in the axial skeleton (e.g., skull or vertebrae) can have serious consequences due to proximity to the brain and spinal cord.

• Movement: The appendicular skeleton enables locomotion and manipulation of objects.

Comparative Table: Axial vs. Appendicular Skeleton

Feature	Axial Skeleton	Appendicular Skeleton
Main Function	Protection, support	Movement, interaction
Major Components	Skull, vertebral column, thoracic cage	Limbs, girdles
Number of Bones	80	126

Additional info:

• The adult human skeleton typically consists of 206 bones.

• Bones are classified by shape: long, short, flat, irregular, and sesamoid.

• Joints between bones allow for movement and flexibility.