The Skeletal System: Axial Division – Structure and Function

The Skeletal System: Axial Division

Introduction to the Skeletal System

The human skeletal system is a complex framework of bones and connective tissues that provides structure, protection, and support for the body. It is essential for movement, organ protection, and serves as a reservoir for minerals.

• Total Bones: The adult human skeleton consists of 206 separate bones.

• Major Divisions: The skeleton is divided into two main sections:

  • Axial skeleton

  • Appendicular skeleton

Divisions of the Skeleton

Division	Main Components	Number of Bones
Axial Skeleton	Skull, Auditory ossicles, Hyoid, Vertebral column, Thoracic cage	80
Appendicular Skeleton	Upper limbs, Pectoral girdle, Lower limbs, Pelvic girdle	126

Axial Skeleton

The axial skeleton forms the central axis of the body and is primarily responsible for supporting and protecting the organs of the head, neck, and trunk.

• Skull bones – Protect the brain and form the structure of the face.

• Auditory ossicles – Small bones in the middle ear involved in hearing.

• Hyoid bone – Supports the tongue and is associated with swallowing.

• Vertebral column – Protects the spinal cord and supports the head and body.

• Thoracic cage – Includes the ribs and sternum, protecting the heart and lungs.

Appendicular Skeleton

The appendicular skeleton consists of the bones of the limbs and the girdles that attach them to the axial skeleton.

• Upper limbs – Arms, forearms, wrists, and hands.

• Pectoral girdle – Clavicles and scapulae, attaching the upper limbs to the trunk.

• Lower limbs – Thighs, legs, ankles, and feet.

• Pelvic girdle – Hip bones, attaching the lower limbs to the trunk.

Functions of the Axial Skeleton

The axial skeleton plays several critical roles in the human body:

• Support and Protection: Provides structural support and protects vital organs such as the brain, heart, and lungs.

• Protection of Special Sense Organs: Shields organs responsible for taste, smell, hearing, balance, and vision.

• Muscle Attachment: Serves as an anchor for muscles that:

  • Adjust the posture of the head, neck, and trunk

  • Move the thoracic cage for respiration

  • Stabilize the appendicular skeleton

Summary Table: Axial vs. Appendicular Skeleton

Axial Skeleton	Appendicular Skeleton
Skull (Cranium and Face) Auditory ossicles Hyoid bone Vertebral column Thoracic cage (Ribs and Sternum)	Pectoral girdle (Clavicle, Scapula) Upper limbs (Humerus, Radius, Ulna, Carpals, Metacarpals, Phalanges) Pelvic girdle (Hip bones) Lower limbs (Femur, Tibia, Fibula, Tarsals, Metatarsals, Phalanges)

Key Terms

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

• Appendicular skeleton: The part of the skeleton consisting of the limbs and girdles.

• Auditory ossicles: Three small bones in the middle ear (malleus, incus, stapes) involved in sound transmission.

• Hyoid bone: A U-shaped bone in the neck that supports the tongue.

• Thoracic cage: The rib cage, which protects the heart and lungs.

Example: Clinical Application

• Injury to the axial skeleton, such as a fractured vertebra or rib, can compromise the protection of vital organs and affect posture and movement.

• Disorders of the appendicular skeleton, such as a broken limb, primarily affect mobility and limb function.