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Electromyography is a procedure, where small needles are placed into the muscles to record electrical activity of the muscle. The activities displayed on an oscilloscope and may be heard through a loudspeaker. Healthy resting muscles produce no electrical activities. However, even a slight contraction of the muscle produces certain electrical activity, that increases as the contraction grows stronger. In spinal motor neuron, peripheral nerve, and muscular diseases, the electrical activities are abnormal. The speed at which conduct of motor nerve impulses, may be measured with nerve conduction study. Motor nerves are stimulated with small electricity charge to trigger the impulses. The impulse is moving along the nerves usually reaching the muscle and resulting it to contract. By measuring the period of time the impulse reaches the muscle, a physician may calculate the speed of the impulse. Similar measurement may be performed for sensory nerves. If weakness of the muscle is resulted from a muscular disorder, the speed of nerve conduction is mostly slowed. The weakness in individuals with myasthenia gravis is resulted from abnormality at the point where the nerve impulses crosses a synapse to the muscles. Recurred impulses are sent along the nerves to the muscles causing increased resistance to the neurotransmitter at the synapse, causing progressively weaker responses over time.
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