The Vertebral Column

The vertebral column (spine) is made up of 33 different bones, called vertebrae.  The first 24 vertebrae are called "articulating" and the last 9 are called "fused."  In addition to the distrinction between articulating and fused, vertebrae are divided into five different categories.  They are:  cervical veretebrae, thoracic vertebrae, lumbar vertebrae, sacrum and coccyx.  See below for a more detailed description of each category.

Cervical Vertebrae
The first seven vertebrae (group 37 on the chart to the left) are called cervical vertebrae.  The cervical vertebrae serve two primary purposes.  The first purpose is to support the head.  The second purpose is to give the neck a flexible framework.  Two of the cervical vertebrae have special names, and serve special purposes.  Vertebra #1 (item 38 on the chart to the left) is called the atlas and is responsible for the movement that allows the head to nod "yes."  Vertebra #2 (item 39 on the chart to the left) is  called the axis and is responsible for the movement that allows the head to nod "no."

Thoracic Vertebrae
The next twelve vertebrae (group 40 on the chart to the left) are called thoracic vertebrae.  This is the part of the spine where the ribs attach.   The thoracic vertebrae move with the ribs, and increase in size as they progress down the spine.

Lumbar Vertebrae
The next five vertebrae (group 41 on the chart to the left) are called lumbar vertebrae.  The lumbar vertebrae are the largest in the spine and serve two primary purposes.  First, the lumbar vertebrae support the majority of the body's weight.  They are also attached to many of the muscles in the back. 

The sacrum (item 42 on the chart to the left) is a large bone located below the lumbar vertebrae.  It is triangular shaped, and forms the back of the pelvic girdle.  In a child the sacrum is made up of 4-5 sacral vertebrae.  Around age 26, the sacral vertebrae become fused together.

The coccyx (item 43 on the chart above) is also called the tailbone.  It is made up of 3-5 bones that become fused together as an adult.  The coccyx is attached to several muscles.

The primary purpose of the spine is to protect the spinal cord, a vital part of the nervous system.  Between the vertebrae are invertebral discs, which are made of fibrous cartilage.  The invertebral discs act as shock absorbers and allow movement of the spine.  When observed from the side the vertebral column has four major curves.  The curves correspond with each group of vertebrae, and are:  the cervical curve, the thoracic curve, the lumbar curve and the pelvic curve (formed by the sacrum and coccyx).  The cervical curve (not present at birth) forms around the time an infant is 3 months old.  The lumbar curve (not present at birth) forms when a child begins to walk.  Both the thoracic curve and the pelvic curve are present at birth.  The curves in the spine allow the human body to stand upright, and to maintain balance.

In addition to protecting the spinal cord, providing rigidity to stand upright and maintaining balance, the spine also provides support for the arms and head as well as providing a place for many muscles, other bones, and organs to attach.