Naked Body: Shivers down the spine

The spinal cord is the highway running down your back that sends messages up and down, but how does it work? David Parker sent us in this...

The spinal cord is a tube made of nervous tissue, which runs through a canal in your backbone. The spinal cord sends signals within these nerves out to the muscles to cause movement. It also processes and relays sensory inputs resulting from movement, as well as sensations from the skin, which enter the spinal cord through the spinal nerves.

In antiquity the spinal cord was considered to be a nerve that connected the brain to the body. People knew that reflexes and other basic movements could still persist in animals such as fish and lizards, even if they had been decapitated. The most famous reflex is probably the knee-jerk reflex, whereby if you tap the ligament just below your kneecap, your thigh muscles contract and your leg kicks out.

Today it is accepted that the spinal cord contains a “central pattern generator”, arising from the activity of special nerve fibres within it. This resembles something like an auto-pilot. The brain sends general commands, like walk or run, which are passed to the the spinal cord, which turns on the appropriate patterns of muscle activity. Though we do still rely on sensory cues for important information, this removes the need for the brain to control every muscle during movement. how clumsy would we be if we had to consciously control every bit of moving ourselves?

The main clinical issue affecting the spinal cord is spinal cord injury, which could occur, for example, in a traffic accident. If the spinal cord is severed, this is equivalent to cutting through an electrical cable: the lesion blocks signals to and from the brain. This gives rise to paralysis and loss of sensation below the lesion site, which likely includes bowel, bladder and sexual dysfunction.

The focus of research into spinal cord injury has been on reconnecting the two ends of the severed spinal cord by regenerating neuronal processes across the lesion site, like patching the electrical cable.

Regeneration can occur in mammals when various inhibitory factors are blocked. However, being able to regenerate the spinal cord has not yet resulted in an effective treatment. This maybe because the undamaged regions of the spinal cord and sensory inputs are altered after lesioning. The changes either side of the lesion mean that this wouldn’t necessarily generate a pre-lesion output. . We would have to know not just how to repair the severed part of the cord, but also how to make sure that the nerve fibres on either side of the lesion return to their normal function.

The difficulty in its repair goes to how complex the spinal cord is. It keeps us going, quite literally.