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EEG / EMG Specialists
EMG :
Electromyography (EMG) and Nerve Conduction Velocity (NCV)
studies are ordered to evaluate for injury or disease of muscle,
nerve roots, and peripheral nerves. They test the condition
of the nerves from the spine, face, and extremities, including
the foot and hand. These studies are normally done together
and are usually performed as a workup for complaints of pain,
weakness, numbness, or tingling.
Unlike radiographic or imaging tests that evaluate structure,
such as an X-ray or MRI, electrodiagnostic studies assess
physiology or biochemical function. Think of a telephone wire
that has static on it. A photograph of the phone would miss
the problem entirely, but with a volt-ohm meter a technician
could determine if there was a bad connection or wire in the
phone itself, the phone line, or at the telephone pole.
During the nerve conduction portion of the study, mild electrical
impulses are sent along the course of a nerve in the arm or
the leg. The electrical impulse will make the muscles in your
arm and leg contract. The sensation you feel is much like
that of a static electric shock.
Electrodes much like EKG patches are placed along the known
course of the nerve. When the nerve is stimulated, it must
transmit the signal along its course. An electrode placed
further down the arm or leg captures the signal as it passes
by. A healthy nerve will transmit the signal faster and stronger
than a sick nerve.
The needle EMG portion of the study involves the insertion
of very thin pin electrodes into the skin. The electrode is
moved around slightly after its insertion. There are two kinds
of electrodes used for EMG studies: Concentric and Monopolar.
Monopolar electrodes are designed for minimal pain and discomfort.
Muscles normally receive constant electrical signals from
healthy nerves, and in return "broadcast" their
own healthy electrical signals. Once inserted into a muscle,
the EMG electrodes record the electrical signal generated
by the muscle. If the muscle is diseased or injured, or if
it does not receive adequate signals from its nerve supply,
then the muscle signals that are broadcast back through the
EMG electrode will show the abnormality.
Since the EMG and NCV study can be uncomfortable many patients
come to the test anxious. Almost all leave feeling they worried
for nothing. Equally important, many are grateful that the
source of their pain, weakness, or numbness has been found
and can now be more effectively treated. |
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EEG:
Electroencephalography is the neurophysiologic measurement
of the electrical activity of the brain by recording from
electrodes placed on the scalp or, in special cases, subdurally
or in the cerebral cortex. The resulting traces are known
as an electroencephalogram (EEG) and |
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represent a summation of post-synaptic potentials
from a large number of neurons. These are sometimes called brainwaves,
though this use is discouraged, because the brain does not
broadcast electrical waves. The EEG is a brain function test, but
in clinical use it is a "gross correlate of brain activity".
Electrical currents are not measured, but rather voltage differences
between different parts of the brain |
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