Dermatomes and Myotomes
Do you want to know what this crazy picture is all about?? READ BELOW!!
Dermatomes?
Dermatomes are areas of skin (derma) that a single nerve from the spinal column is associated with. Nerves come out from the spinal column and innervate our arms and legs. They connect to our muscles like brain powered extension cords. Why should you know about them? They act like a map, and can help determine the source of a spinal issue. Ever have a shooting pain somewhere in your body? A pinched nerve? Most of the time, those pains may be signals stemming from an issue within the spine, whether it is stenosis, bone spur, disk herniation, or bulge. It’s not a perfect science: sometimes the muscles that nerves run through can also be the source of a nerve pinch. Dermatomes specifically chart spinal nerves along your skin. Experiencing symptoms along a specific dermatome can help inform doctors where the spine may be affected. Doctors will give certain skin tests along those lines for numbness including a pinprick test (ouch) or using a cotton ball, pen, or Q tip. Patients can also explain a tingling or numbness running down a certain line on their body, which can help a doctor’s determination to which spinal segment may be problematic. If you have pain in a specific area, you can refer to the chart provided. Although, it is no substitute for going to see your doctor when needed!
Myotomes?
There are also myotomes. Myotomes are spinal nerves that are connected to a specific muscle (myo) action.
There are 8 cervical nerves (note C1 has no dermatome), 12 thoracic nerves, 5 lumbar nerves and 5 sacral nerves. All of these nerves have a dermatome. But 16 of these 31 nerves have a specific myotome that controls voluntary muscle movement.
Here are the areas of action that can be affected by spinal nerves
C5- shoulder abduction, C6– Elbow flexion Wrist extension, C7 – Elbow extension,
C8 – Finger flexion, T1 – Finger abduction, L2 – Hip flexion, L3 – Knee extension,
L4 – Ankle dorsiflexion, L5 – Great toe extension, S1 – Ankle plantarflexion
Source: Physiopedia
Doctors can test these movements to get to the source of the problem. In 2016, I had a pretty serious back injury. I herniated my L5/S1 holding my 2 year old niece by her feet and swinging her side to side. That was just the straw that broke the camel's back. My 20 plus years of dancing probably didn’t help either. I had no pain from the injury, luckily, but numbness and weakness in my right foot. When I had no feeling or reflexes in my foot, my doctor sent me to a “first thing in the morning” MRI which confirmed my injury. If you look at the chart, you can see how the L5/S1 dermatome runs to the foot, so the doctor knew it was a spinal issue. L5 myotome is big toe lifting up (extension) - the beauty of having a blog is I learn so much. My right big toe does not lift, so now I am working on it! More obviously, when I was freshly injured, I couldn’t rise up to the ball of my foot. If we look at the muscle action of the myotomes, S1 is ankle plantar flexion, the action of the ankle when you rise to the ball of your foot. The disk herniated to the right, which affected these nerves. After 5 years, I now can rise to the ball of my foot, but I still have a tiny bit of residual numbness on the skin of the foot I don’t think will come back. It’s now a faded memory and permanent reminder of a time I was injured. Thank goodness I am fine now, but we all have different phases of our lives when our health is at its peak, and when it is in need of rest and recovery. That is what makes us human.