Spinal cord

 

The vertebral column consists of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx.

It is situated in the dorsal aspect of the torso. It houses and protects the spinal cord in its spinal canal.

The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells

It begins at the occipital bone and extends down to the space between the first and second lumbar vertebrae; it does not extend the entire length of the vertebral column. The enclosing bony vertebral column protects the relatively shorter spinal cord.

The spinal cord is thus part of the physical nervous system and functions primarily in the transmission of neural signals between the brain and the rest of the body. It has three major functions:

• as a conduit for motor information, which travels down the spinal cord
• as a conduit for sensory information which travels up the spinal cord
• and finally as a center for coordinating certain reflexes

The spinal cord is protected by three layers of tissue that surround the canal.

• The pia mater is the innermost protective layer. It is ‘highly vascularised ‘ and very delicate and it is tightly associated with the surface of the spinal cord.  The pia mater carries blood vessels which supply nutrients and remove waste from nerve tissue.  The pia mater is made of collagen and elastic fibres

• The arachnoid mater is the middle protective layer. Its name comes from the fact that the tissue has a spiderweb-like appearance. The space between the arachnoid and the underlying pia mater is called the subarachnoid space. The subarachnoid space contains cerebrospinal fluid (CSF).

• The dura mater is the outermost layer, and it forms a tough protective coating. The dural sac ends at the vertebral level of the second sacral vertebra. But the dura mater doesn’t end when it gets to the skull.  Instead it extends into the skull forming a sort of sack that encloses a number of organs in the brain as well as the spinal cord.  It thus forms the outermost of the three layers of the meninges surrounding the brain and spinal cord. The other two meningeal layers being the pia mater and the arachnoid mater.  The dura surrounding the brain and the spinal cord is responsible for keeping in the cerebrospinal fluid.

In cross-section, the peripheral region of the cord contains neuronal white matter tracts containing sensory and motor neurons. Internal to this peripheral region is the grey, butterfly-shaped central region made up of nerve cell bodies. This central region surrounds the central canal, which is an anatomic extension of the spaces in the brain known as the ventricles and, like the ventricles, contains cerebrospinal fluid.

 The spinal cord is also supplied with blood by three arteries that run along its length starting in the brain, and many arteries that approach it through the sides of the spinal column. These travel in the subarachnoid space and send branches into the spinal cord.