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This tape describes the musculo-skeletal system of the trunk. We’ll look at the trunk in four sections. In this first section we’ll look at the spine, and the spinal cord. In the following sections we’ll look at the thorax, the abdomen, and the pelvis.

The spine is known in anatomy as the vertebral column, or spinal column. In looking at it, we’ll look first at the bones, then at the structures that hold the bones together, then at the main muscles which move it. After that, we’ll add the spinal cord, and the spinal nerves to the picture.

Here’s the vertebral column It consists of twenty-four separate vertebrae, the sacrum, and the coccyx. There are seven cervical vertebrae, twelve thoracic vertebrae, and five lumbar vertebrae. The sacrum consists of five vertebral segments fused together. The coccyx - our vestigial tail - consists of three or four tiny segments.

The highest cervical vertebra articulates with the skull; the thoracic vertebrae articulate with the ribs; and the sacrum articulates with the two innominate bones to form the pelvis.

When seen from in front, the spine appears straight, but when we look at it from the side, we see that it’s markedly curved. The lower cervical vertebrae form a forward curve, the thoracic vertebrae form a backward curve, the lumbar vertebrae curve forward again, and the sacrum curves sharply backward.

These peices of material represent the intervertebral disks, which we’ll be looking at shortly.

The vertebrae of each region are numbered from above down. Instead of using the words cervical, thoracic, lumbar, and sacral, we often just use the letters C,T, L, and S. For example, we’d call the fourth lumbar vertebra the L4 vertebra.

There are marked differences between vertebrae of different regions, but they all have some basic features in common. We’ll look at a typical thoracic vertebra to see what these features are.

In front, this cylindrical mass of bone, the body of the vertebra, supports the weight of everything that’s above it. Behind, there’s a set of bony plates and projections which serve three functions: to protect the spinal cord; to give attachment to muscles and ligaments; and to articulate with the adjoining vertebrae.

This arch of bone, the neural arch, encloses the spinal cord. The space that’s surrounded by the arch and the back of the body is called the vertebral foramen.

The series of vertebral foramina create the tubular space that contains the spinal cord. The space is called the vertebral canal.

This part of the neural arch is called the lamina, this part is the pedicle. There’s a small notch in the upper edge of the pedicle, and a larger notch in the lower edge. Together, the notches above and below form this opening on each side, the intervertebral foramen. A spinal nerve emerges through each intervertebral foramen.

Arising from the neural arch are three large bony projections called processes - a spinous process in the midline, a transverse process on each side. Also arising from the neural arch are four articular processes, two above, and two below.

The lower ones face forward, the upper ones face backward. The articular processes of adjoining vertebrae interlock, forming a pair of synovial joints which permit movement between adjoining vertebrae.