Spinal Anatomy 101 ~ Spinal Bones

Stanley Hoppenfeld, MD
Michael S. Zeide, MD
illustrations by James Capizzuto

The spine is one of the most important components of the human architecture. It is composed of bones, joints, muscles, ligaments and nerve structures.

The spine is composed of 33 bones. These bones are divided into sections.

Section 1 – The Cervical Spine The cervical spine begins at the base of the skull. There are seven vertebrae in this area with eight pairs of cervical nerves responsible for controlling the neck, arms and upper body. These vertebrae are sturdy, which is required to support the weight of the head and vertebral stress during movement.	Figure 1
	Figure 2

Figure 3	Section 2 – The Thoracic Spine Starting below the last cervical vertebrae begins the thoracic spine. There are 12 vertebrae and 12 pairs of ribs plus nerve roots responsible for the midsection of the body. The ribs form the chest wall and protect many internal organs.
	Section 3 – The Lumbar Spine Although there are normally five lumbar bones or vertebrae, some people are born with one more or less. These spinal bones are the largest and strongest in the back. This part of the spine carries the bulk of the body's weight. There are five pairs of lumbar nerves responsible for movement and sensory functions in the lower extremities.

Sections 4 & 5 – The Sacrum and Coccyx Following the last lumbar vertebra is a mass of five smaller bones naturally fused together in the shape of a triangle. This is the sacrum. The coccyx or tailbone is attached to the lower end of the triangle and is composed of four little bones fused together. The sacrum and coccyx do not look like any other spinal bone. The pairs of nerve roots originating from this area are responsible for the action of the pelvic organs and buttock muscles.

Figure 4

Why does the spine curve?

The spine curves gently at the cervical, thoracic and lumbar regions. The curves serve as springs in a coil to distribute mechanical stress as the body moves.

Credits

(Material provided by Stanley Hoppenfeld, MD and Michael S. Zeide, MD, illustrations by James Capizzuto, Orthopaedic Dictionary, 1994.)

Figure 1 (Image courtesy of Wheeless' Textbook of Orthopaedics, 1996, C. R. Wheeless, MD.)
Figure 2 (Image courtesy of Orthopaedic Dictionary, 1994, Stanley Hoppenfeld, MD and Michael S. Zeide, MD, illustrations by James Capizzuto.)
Figure 3 (Image courtesy of SYAB "Save Your Aching Back", A Patient's Guide)
Figure 4 (Image courtesy of Wheeless' Textbook of Orthopaedics, 1996, C. R. Wheeless, MD.)

More on spinal joints
Spinal structures
Spinal Ligaments
Return to anatomy
Spinal Cord & Nerves