The Spinal Cord

Introduction

The spinal cord is a cable about 43cm in length running from the brain stem to the lower back. It contains two types of tissue. The inner core is gray matter made up of nerve cell bodies, unmyelinated axons, glial cells and blood vessels; the outer white matter is mainly composed of tracts of myelinated axons thath relay impulses to and from the spinal cord and the brain.

The position of the medulla spinalis varies with the movements of the vertebral column, its lower extremity being drawn slightly upward when the column is flexed. It also varies at different periods of life; up to the third month of fetal life the medulla spinalis is as long as the vertebral canal, but from this stage onward the vertebral column elongates more rapidly than the medulla spinalis, so that by the end of the fifth month the medulla spinalis terminates at the base of the sacrum, and at birth about the third lumbar vertebra.

Extent of spinal cord

During the body's growth and development, the spinal cord does not continue to lengthen the way that the spinal bones do: it therefore occupies only the first two-thirds of vertebral column. Cylindrical and slightly flattened, the spinal cord is about as thick as a finger for most of its length; extending from the lower part if the spinal cord is a cluster of individual nerve fiver called cauda equina.

Spinal nerves

Through 31 pairs of spinal nerves, the spinal cord is connected to the rest of the body; via these nerves, the spinal cord sends and receives information to and from the brain. The spinal nerves run through gaps between adjacent vertebrae and enter the back and front of the spinal cord as spinal nerve root.

The project

First of all, i made some sketches of the spinal cord to better understand his structure and to obtain the points for the curve.

The Meninges

These are the three protective layer of connective tissue for the spinal cord.

• The Dura Mater: is the outermost layer, and it forms a tough protective coating.
• The Arachnoid: is the middle protective layer. Its name comes from the fact that the tissue has a spiderweb-like appearance.
• The Pia Mater: is the innermost protective layer. It is very delicate and it is tightly associated with the surface of the spinal cord.

To realize them, i started with the base of Dura mater by drawning a BEZIER curves and obtaining the surface (shown in the picture below) with the point interpolation (always using BEZIER, but with selector S1).

The boundary surface've been realized through createCylSurface, in which i've used the PLASM function CYLINDRICAL_SURFACE.

With the affine trasformation T and S applied to the contour and the base, I realizad the other meninges and close them, as you can see in the following picture.

The Fiber Tracts of the spinal cord

Myelinated nerve fibers in the spinal cord are grouped together according to the direction and the type of impulses between just a few pairs of spinal nerves.

The gray matter of spinal cord is organizad into areas called horns, which are:

• Dorsal (back) horns: neuron cell bodies here receive information from sensory nerve fibers all around the body about sensation, including touch, temperature, awareness of muscle activity, and balance.
• Lateral (side) horns: existing only at certain levels of the spinal cord; neuron bodies in the lateral horns regulate the internal organs.
• Ventral (front) horns: these contain neuron bodies that send fibers to the skeletal muscles, cousing contraction and movement.

The nerve in the fiber tracts have been realized with BEZIER and CYLINDRICAL_SURFACEand the traslation, through the affine trasformation T, of the nerve choosen as a sample.

Spinal Nerve and Sensory Root

The sensory nerve roor carries the impulses about bodily sensation. They converge to form sensory roots at the back of the spinal cord. Impulses are then conveyed to the brain via nerve fiber tracts.

Each spinal nerve has a dorsal (posterior) sensory root ganglion, which is a cluster of nerve cell bodies.

The motor nerve root are bundles of fibers, which leave the front of the spinal cord. I realized them with my function createConicalSurface, which help me drawning the CONICAL_SURFACE.

The fibers conduct impulses from the central nervous system to control voluntary movement and involuntary processes such as digestion.

The nerves aren't symmetrical, then i can't use the affine trasformations. But by changing the control points and applied the right functions, i obtain the following model:

Disclaimer

I found some material (including text and images) through Google, Wikipedia and in the book The Human Body, so they belong to their respective owners.