Electromyography: Definition & Use

Instructor: Danielle Haak

Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

Electromyography is a medical procedure that analyzes how the muscles receive information from the nerves. It can be used to gain information about healthy or damaged muscles. This lesson will describe the procedure and why it's used.

What Is Electromyography?

Betty is a middle aged woman who has just started to notice that her arm has been twitching on a regular basis. She can't figure out why, so she decides to go to the doctor to see if this odd muscle malfunction is a sign of something else.

What if we could easily assess the health of our muscles without an invasive procedure? Well, we can! See, motor neurons are the nerve cells that transmit information (or impulses) between the brain and muscles and are the cells that signal a muscle to do something. We've created a medical procedure called an electromyography (EMG) which monitors the electrical signals muscles receive and send to motor neurons. It's a pretty cool medical advancement if you think about it.

When a motor neuron signals a muscle to move (usually to tighten), the signal comes in the form of electricity. An EMG can read these electrical pulses and record them. A computer then takes this information and creates a graph or table output that can be interpreted and analyzed by a doctor. Typically, a properly functioning muscle at rest will not produce an electrical signal.

How it Works

How does this work? Well, the EMG uses small devices called electrodes to monitor for electrical signals in the body. In some cases, the electrode is placed on the surface of the skin, and in other cases, the electrode is inserted on a needle into the muscle we want to analyze.

For example, when Betty visits the doctor, a nurse will place a needle into an arm muscle, and then the Betty will contract (or tighten) the muscle. This will result in an electrical signal that is picked up by the electrode and recorded.

To visually analyze the output of the EMG, a computer is used to draw a graph representing the electrical signals. This is displayed on a monitor called an oscilloscope. Even cooler is the ability to 'listen' to the signal through the use of an audio amplifier. When an audio amplifier is connected, a brief 'ting' noise is created every time the muscle contracts.

EMG results can be displayed on an oscilloscope.
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Why Use Electromyography?

Now that we know how this procedure works, why would it be useful? Electromyography is used to identify nerve abnormalities, muscle dysfunction, or disruptions in the nerve-muscle connection. For example, if a patient is experiencing an unexplained muscle twitch like Betty, an EMG can be used to figure out what's causing the twitch.

Specifically, an EMG can be used to diagnose conditions like:

  • carpal tunnel syndrome
  • a herniated disc in the back (ouch!)
  • amyotrophic lateral sclerosis (a condition affecting motor neurons)
  • muscular dystrophy (a muscle disorder)
  • myasthenia gravis (a condition affecting the nerve-muscle connection)

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