The term tetraplegia refers to a condition that causes total or partial paralysis in all four limbs, including the whole of the body. Tetraplegia can be caused by injury or illness, both  of which can damage the spinal cord permanently between the levels of  C1 - 7. The term tetraplegic refers to an individual who suffers from tetraplegia. Quadriplegic is the American terminology for tetraplegic.

The easiest way to describe how the spinal-cord works is to imagine that it is a motorway with cars running in both directions. The cars travelling down are carrying signals from your brain that tell your body what to do, i.e. wiggle your fingers or move your arms for instant. The cars traveling upwards towards the brain are carrying sensation which obviously enables you to feel pain. If a complete section of the motorway was removed then cars would not be able to travel in either direction and would not be able to deliver the signals and sensation. If you are not able to deliver signals that tell your legs to move then you are not able to walk. If sensation cannot be delivered to your brain then you cannot feel anything below the section of motorway that has been removed. 

spinal cord 3The spinal cord runs through seven vertebrae, these are called the cervical vertebrae, commonly abbreviated to C1 - C7.  In most cases, somebody who has damaged their spinal cord in the upper region of their neck suffers a far serious paralysis than somebody who damaged their spinal cord further down in the neck region.  Not every injury is the same, even if the level of injury is identical, the severity of the paralysis is governed by how severely the spinal cord has been traumatised.  A complete break to the spinal cord normally results in complete paralysis below the level of injury. However, an incomplete injury which means the damage to the spinal-cord is less severe can often result in much less paralysis.  It really differs greatly, some people are able to move fingers and toes and that's all, other people may be able to move one leg and maybe a couple of fingers, whilst some tetraplegics can manage to walk to a certain extent.  Because the spinal cord is so complex nearly every spinal-cord injury is slightly different, even if the level of injury is the same.  I have met fellow tetraplegics with the same level of injury as me who are able to transfer into vehicles by themselves, get in and out of bed, whilst others are much less mobile and don't have anywhere near the movement I do.

If you look at the brain as being the electricity supply and the spinal cord as the wire leading to all appliances, this is basically how your spinal column works.  Let's say you have several junctions coming off that wire that lead to different parts of your body, if you damage the wire above that level then nothing below is going to work anymore.  Obviously, this is the worst scenario, if that wire is only partially damaged then in many cases some movement and feeling can still exist below the injury, this is known as an "incomplete spinal-cord injury".

Young adults are more often the victim of spinal-cord injury, the majority of whom are males.  Car and motorcycle accidents are responsible for about half of SCI cases. Many cases of tetraplegia have been caused by a sporting accident such as rugby, this is particularly common in the UK. Diving is also one of the most common causes of tetraplegia, in most cases young men diving into shallow water.

C1 - C3 complete injuries normally result in complete paralysis of all limbs.  C1/2 and sometimes C3 will in many cases require ventilation to aid breathing.  However, many C3 are able to breathe without the need for ventilation.

C4 - C5 complete injuries normally result in complete paralysis below chest level.  Most patients have shoulder and limited arm movement.  Limitations are a lack of triceps muscles, no wrist extensors, and no finger movement.

C6 -C7 subjects often have quite a bit more movement than C5 for instance. C6 normally have wrist extensors but still no hand or triceps movement.  However, their strength is in many cases, a little better than a C5 injury. C7 have good arm movement and functional triceps which makes life so much easier as you can often transfer yourself. They may often have slight hand movement.

Complete tetraplegia normally results in no bowel or bladder function.

This is just a brief description of tetraplegia, hopefully, it should give you an idea of the different levels of break

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