Electromyography (EMG)
measures the response of muscles and nerves to electrical activity.
It's used to help determine muscle conditions that might be
causing muscle weakness, including muscular dystrophy and nerve
disorders.
How Is an EMG Done?
Muscles are stimulated by signals from nerve cells called
motor neurons
. This stimulation causes electrical activity in the muscle, which
in turn causes the muscle to contract or tighten. The muscle
contraction itself produces electrical signals.
For the purpose of EMG, a needle electrode is inserted into the
muscle (the insertion of the needle might feel similar to an
injection). The signal from the muscle is then transmitted from the
needle electrode through a wire (or more recently, wirelessly) to a
receiver/amplifier, which is connected to a device that displays a
readout. The results are either printed on a paper strip or, more
commonly, on a computer screen.
What Can an EMG Diagnose?
EMGs help diagnose three kinds of diseases that interfere with
normal muscle contraction:
- diseases of the
muscle itself
(most commonly, muscular dystrophy in children)
- diseases of the
neuromuscular junction
, which is the connection between a nerve fiber and the muscle it
supplies
- diseases "upstream" in
nerves and nerve roots
(which can be due to either nerve damage or ongoing nerve
injury)
When Are Results Ready?
Results are available immediately but a trained medical
specialist, usually neurologist, is needed to analyze and interpret
them.
Reviewed by:
Steven Dowshen, MD
Date reviewed: September 2007
Originally reviewed by:
Frederick A. Meier, MD
Note: All information is for educational purposes only. For specific medical advice,
diagnoses, and treatment, consult your doctor.
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