Question
hi,
thankyou for the response,
however, i am still confused. from my understanding simple relexes dont involve the brain, they just go through the spinal cord to increase the speed of response. i thought that the other neurones that send messages to the brain would be interrupted but the actual reflex would still be okay. so I figured that if the neurones below the injury were okay then some reflexes might still occur. We teach that the knee jerk only involves one sensory and one motor neuron, so do you know why an injury that doesnt affect either of these will still prevent the reflex as i understand that is what you are saying. I thought that only the pain or feeling associated with the reflex would not be felt.

sorry about the convoluted question. hope it makes some sense.
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Followup To

Question -
Hi John,
I was talking to a high school class today about reflex arcs and it crossed my mind that reflexes (eg: knee jerk)should still take place in para/quadriplegics. Is this the case?
Thankyou so much for your time.
Fiona

Answer -
Hi Fiona,
Thanks so much for your question.

Ironically, that's one of the first things doctors test to find the extent of someone's paralysis.

When someone suffers paralysis from a spinal cord injury, it mean the comunication between the brain and the body has been interrupted. When the doctor checks the reflexes, like the knee jerk, he is testing that comunication from the body to the brain and back to the body.

I hope this helps and if you have any more questions, please feel free to ask me anytime.

Thanks again,
John McKinzie

Answer
Hi Fiona,

Basically, when a doctor checks the reflexes of someone with a spinal cord injury, he is testing to find out if the patient has a complete or incomplete injury.

The messages still have to travel through the spinal cord. In other words, it's like traveling in a small town and you want to go to another town but there's only one way. You travel on some small roads until you merge onto a larger road and then to the interstate highway. You are almost to your destination but you encounter a road block and can't go any farther.

In the case of a spinal cord injury, the neurons are still working but they don't know what to do because the sensory and motor has been interrupted.

After I had my accident and was stable, the neurologist tested my knees, ankles and elbows at which time he was able to determine the extent of my injury and what was affected. Sadly to say, there no reflex response.

Something else that may interest you are muscle spasms. It works along the same lines. For example, if you feel something on "your" leg, in a split second, a message is sent to the brain then interputed and sent back to the leg. You would jerk away, relax or do something else, depending on what you felt. In the case of a spinal cord injury, that message travels towards the brain but is stopped at the level of the injury and returns as a "garbled" message. The muscle does 1 of 2 things - they  contract or there is no response. In my case, they contract and more often than not, the spasms become severe and very painful.

I hope this has helped answer your question. If it hasn't or if you have another question, please feel free to ask me and I'd be more than happy to help.

Thanks,
John McKinzie