Axial Skeleton: Vertebral Column & Thoracic Cage Study Notes

Axial Skeleton

Overview

The axial skeleton forms the central axis of the human body and is essential for support, protection, and movement. It consists primarily of the vertebral column and the thoracic cage, which together protect vital organs and provide attachment points for muscles.

• Vertebral Column: Composed of 26 bones, including cervical, thoracic, lumbar vertebrae, sacrum, and coccyx.

• Thoracic Cage: Includes 24 ribs and 3 bones of the sternum.

Learning Outcomes

• Differentiation of Body Cavities: Understand the body cavities bordered by the thoracic cage.

• Identification and Description: Recognize and describe the bones of the vertebral column, ribs, and sternum, and understand their significance.

• Joints: Identify the joints connecting these bones.

• Movement: Describe the basic movement of the thoracic cage during breathing.

Vertebral Column

Structure and Regions

The vertebral column is a flexible, segmented structure that supports the head and trunk, protects the spinal cord, and provides attachment for ribs and muscles.

• Cervical Vertebrae (7): Located in the neck region.

• Thoracic Vertebrae (12): Articulate with the ribs.

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

• Sacrum (1): Formed by fusion of 5 sacral vertebrae.

• Coccyx (1): Formed by fusion of 4 coccygeal vertebrae.

Functions of the Vertebral Column

• Support: Maintains upright posture and supports the head.

• Protection: Encloses and protects the spinal cord.

• Movement: Provides flexibility and movement of the trunk.

• Metabolic Functions: Stores minerals and lipids; site of hematopoiesis (blood cell formation).

Thoracic Cage

Structure

The thoracic cage protects the heart and lungs and supports the shoulder girdles and upper limbs. It consists of ribs, sternum, and thoracic vertebrae.

• Ribs (24): 12 pairs, each articulating with thoracic vertebrae.

• Sternum (3): Manubrium, body, and xiphoid process.

General Features of Ribs

• Head: Articulates with vertebral bodies.

• Neck: Connects head to shaft.

• Tubercle: Articulates with transverse process of vertebra.

• Shaft: Main portion of the rib.

• Costal Groove: Houses nerves and blood vessels.

Major Body Cavities

Body Cavity Organization

The axial skeleton helps define and protect several major body cavities, each containing vital organs.

• Cranial Cavity: Contains the brain.

• Vertebral Canal: Contains the spinal cord.

• Thoracic Cavity: Contains lungs, heart, and mediastinum.

• Abdominal Cavity: Contains digestive organs.

• Pelvic Cavity: Contains reproductive and some digestive organs.

Thoracic Cavity Subdivisions

• Pleural Cavities: Surround each lung.

• Pericardial Cavity: Surrounds the heart.

• Mediastinum: Central compartment between pleural cavities; contains heart, trachea, esophagus.

Summary Table: Axial Skeleton Components

Region	Number of Bones	Main Features
Cervical Vertebrae	7	Neck region, supports head
Thoracic Vertebrae	12	Articulates with ribs
Lumbar Vertebrae	5	Lower back, largest vertebrae
Sacrum	1 (5 fused)	Pelvic region, fused vertebrae
Coccyx	1 (4 fused)	Tailbone, fused vertebrae
Ribs	24	Protect thoracic organs
Sternum	3	Manubrium, body, xiphoid process

Example: Thoracic Cage Movement During Breathing

• During inhalation, the rib cage expands as the ribs move upward and outward, increasing thoracic volume.

• During exhalation, the rib cage depresses as the ribs move downward and inward, decreasing thoracic volume.

• This movement is often described as the bucket handle and pump handle mechanisms.

Additional info: The notes reference Marieb's Anatomy & Physiology textbook, Chapter 7, for further reading on the vertebral column and thoracic cage.