Why do I have pain?November 26, 2012
When you go to physical therapy, at the beginning of each session you might receive a heat pack, but in addition to this you might be set up with some electrodes and receive something called electrical stimulation. You might have a basic idea of what this does in that it decreases pain, but how exactly does it do this?
The main theory to explain how electrical stimulation helps decrease pain is by something called the Gate Theory. In order to understand this you must first know a few things about the nervous system. The central nervous system is composed of the brain and the spinal cord. Nerves, in this case those that give your brain information about sensation and those that give your brain information about pain, go from different parts of your body to the spinal cord. The spinal cord then sends information up to the brain about what the body is experiencing and then sends information back down to let you know how to respond. For example if you hit your elbow on something, the nerves in your elbow send information up through your spinal cord to the brain which senses you hurt yourself. In response to this the brain as a general reaction may send information down to the muscles in your other arm to rub the elbow you hit to reduce the pain. Rubbing your elbow works in a similar way that electrical stimulation does in that it stimulates a particular pathway that prevents you from sensing pain. Let’s take a closer look at what’s going on.
Pain nerve fibers and sensory nerve fibers are not the same. Nerve fibers in general are sometimes covered in something called myelin. If a nerve fiber has myelin on it, the nerve can transmit information to the brain faster. Pain nerve fibers can only have a small amount of myelin or none at all whereas sensory nerve fibers typically have more myelin. This is a big reason why we rub our elbow when we hit it. By rubbing it we stimulate sensory nerve fibers which are able to beat the pain signal to the brain. But then why doesn’t the pain signal get to the brain immediately after we sense that we are rubbing our elbow?
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There is more that happens at the level of the spinal cord. In the spinal cord there is something called an inhibitory interneuron (a fancy way of saying a nerve cell that prevents pain signals from going to the brain). When pain nerve fibers are stimulated during times such as when you hit your elbow, the signal that goes to the spinal cord turns off the inhibitory interneuron. This allows the pain signal to go to the brain. The signal gets there via a transmission cell since the cell that prevents pain signaling is no longer turned off-it’s a double negative so it cancels out and you have pain.
If you then begin to rub your elbow, you stimulate the sensory nerve fibers. Sensory nerve fibers turn on the inhibitory interneuron at the spinal cord. When you turn on the inhibitory interneuron you prevent the pain signal from going to the brain. So not only do sensory fibers transmit information to the brain faster (via a transmission cell), but they also prevent the pain signal from reaching the brain by turning on the inhibitory interneuron (which keeps the pain signal from getting to the transmission cell). So why don’t we have you rub your elbow for 20 minutes before therapy?
First, you’d probably get tired after the first minute of rubbing your elbow, but also patient’s have reported that electrical stimulation has allowed them to experience a decreased amount of pain for extended periods of time after having received it. Something you might notice when you are receiving it is that it seems to turn off and on- so one minute you’ll feel a tingling sensation (which is the electrical current stimulating your sensory nerve fibers) and then you won’t feel anything.
The unit that is transmitting the electrical current has been specifically set to do this to avoid something called accommodation. Accommodation is something that happens when you are exposed to a stimulus such as rubbing or an electrical current or a certain temperature for an extended period of time. Your body get’s used to the stimulus and you no longer notice it as much. For example when you jump into a swimming pool, initially the water might feel cold, but after a while of moving around you no longer notice how cold it is. Having the electrical current turn off and then on repetitively allows you to avoid the affects of accommodation/ prevents your body from getting used to the stimulation so that it is actually able to help calm down your pain.
Electrical stimulation is a great tool for decreasing pain which allows the physical therapist to help you make gains in range of motion, strength or endurance.
For more information on physical therapy head to www.totalperformancept.com.