Anatomy & Physiology

The human spine is at the centre of the body, connecting the head to the pelvis, and supporting everything in between.  The spine  is straight when viewed from behind, but from the side it is shaped like an 'S'.  This shape allows for some shock absorption.  The spine consists of 27 to 29 bones (vertebra). The top 7 bones are the neck (cervical spine), the next 12 is the middle back (thoracic spine) and the next five are the low back (lumbar spine). The next bone is called the sacrum, it is a wedge-shaped structure connecting the spine to the pelvis.  At the bottom is the coccyx which ranges from 2 to 4 bones.  Each vertebra need only move a little bit but the total can move a long way.

Whilst the shape of each vertebra is slightly different to the one above, they do have a lot in common.   The large lump of bone at the front is called the body - it supports most of the weight which is why they get larger as we progress down the spine.  Coming off the body of the vertebra is a ring of bone, within which the spinal cord is located.  Projecting off the ring of bone are small processes that act as levers and points of attachment for the muscles and ligaments.  

Each vertebra is connected to its neighbour by two facet  joints above and below, which control movement and provide stability.  The structure between each vertebra is called the intervertebral disk.  It is like a big rubber spacer that keeps the vertebra apart and yet allows for movement.  On the inside of the disk is a gel-like substance (nucleus pulposus), just like your blue toothpaste.  On the outside is a thick, tough, tissue (annulus fibrosus), arranged in layers like an onion.  This is the wall of the disk and this keeps it all together. The vertebra are connected by very strong ligaments and muscles.  Some of the ligaments and muscles go from one vertebrae to the next whilst others cross many bones before connecting to a vertebra higher up. The muscles that attach from one vertebrae to the next control positioning, while the muscles that cross many vertebra are the prime movers.  The role of the short muscles is to provide dynamic stability by constantly adjusting to maintain the vertebra in the correct position, so that the long muscles can move the spine as a whole. Like every other structure in the body there are also blood vessels and nerves, etc., supplying all of the tissues in the spine.