The Human Skeleton: Structure and Organization

The Skeleton

Introduction to the Skeleton

The human skeleton is the internal framework that supports the body, protects vital organs, and enables movement. The term "skeleton" comes from the Greek word stereopsis, meaning "dried up body." The skeleton is divided into two major parts: the axial skeleton and the appendicular skeleton.

• 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, including the pectoral girdle & upper limbs and the pelvic girdle & lower limbs.

Functions of the Skeleton

• Support: Provides structural support for the entire body.

• Protection: Shields vital organs such as the brain, heart, and lungs.

• Movement: Acts as levers for muscles to produce movement.

• Mineral Storage: Stores minerals such as calcium and phosphorus.

• Blood Cell Production: Houses bone marrow, which produces blood cells (hematopoiesis).

Axial Skeleton

Major Regions of the Axial Skeleton

The axial skeleton consists of the following regions:

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

• Vertebral Column: Supports the spinal cord and provides flexibility and movement.

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

The Skull

The skull is the body's most complex bony structure, composed of 22 bones. It encloses the brain and forms the framework of the face. The skull is divided into the cranium and facial bones.

• Cranium: Encloses and protects the brain; provides attachment for head and neck muscles.

• Facial Bones: Form the framework of the face, house cavities for sense organs, provide openings for air and food, and anchor teeth.

Key Cranial Bones: Frontal, Parietal (2), Temporal (2), Occipital, Sphenoid, Ethmoid.

Key Facial Bones: Mandible, Maxillae (2), Zygomatic (2), Nasal (2), Lacrimal (2), Palatine (2), Inferior nasal conchae (2), Vomer.

Appendicular Skeleton

Pectoral Girdle & Upper Limbs

The pectoral girdle attaches the upper limbs to the axial skeleton and consists of the clavicle and scapula. The upper limb includes the humerus (arm), radius and ulna (forearm), carpals (wrist), metacarpals (hand), and phalanges (fingers).

• Clavicle: Collarbone; connects the arm to the body.

• Scapula: Shoulder blade; provides attachment for muscles.

• Humerus: The only bone of the arm; articulates with the scapula at the shoulder and with the radius and ulna at the elbow.

• Radius & Ulna: Bones of the forearm; allow for rotation and movement of the wrist.

• Carpals, Metacarpals, Phalanges: Bones of the wrist, hand, and fingers.

Pelvic Girdle & Lower Limbs

The pelvic girdle attaches the lower limbs to the axial skeleton and consists of the hip bones (os coxae). The lower limb includes the femur (thigh), patella (kneecap), tibia and fibula (leg), tarsals (ankle), metatarsals (foot), and phalanges (toes).

• Os Coxae: Hip bones; formed by the fusion of ilium, ischium, and pubis.

• Femur: Thigh bone; longest and strongest bone in the body.

• Patella: Kneecap; protects the knee joint.

• Tibia & Fibula: Bones of the lower leg; tibia is weight-bearing, fibula provides stability.

• Tarsals, Metatarsals, Phalanges: Bones of the ankle, foot, and toes.

Summary Table: Major Divisions of the Skeleton

Division	Main Components	Function
Axial Skeleton	Skull, Vertebral Column, Thoracic Cage	Protection, Support
Appendicular Skeleton	Pectoral Girdle & Upper Limbs, Pelvic Girdle & Lower Limbs	Movement, Manipulation

Example: The Humerus

The humerus is the bone of the upper arm. It articulates proximally with the scapula at the shoulder and distally with the radius and ulna at the elbow. The humerus serves as an attachment site for several muscles and is essential for arm movement.

Additional info: The skeleton also plays a role in endocrine regulation by releasing osteocalcin, a hormone involved in glucose metabolism.