Electromyography

Electromyography (EMG) records electrical activity in skeletal muscles, usually with needle electrodes, to assess muscle function and the nerves that control it.

Needle electromyography: An EMG technique that records electrical activity from muscle using a fine needle electrode. It samples activity within individual muscles during rest and voluntary contraction.
Radiculopathy: A disorder caused by compression or irritation of a spinal nerve root. Needle EMG can identify patterns of muscle denervation consistent with a damaged nerve root.
Motor unit: A motor neuron and all the muscle fibers it activates. EMG signals reflect the activity of motor units within the sampled muscle.
Surface electromyography: A method that records muscle electrical activity through electrodes placed on the skin. Unlike needle EMG, it samples signals noninvasively but less selectively.
Nerve conduction study: A test that measures how electrical impulses travel through peripheral nerves. It is commonly paired with EMG to distinguish nerve disorders from muscle disorders.
Peripheral neuropathy: Damage or disease affecting nerves outside the brain and spinal cord. Combined electrodiagnostic testing can characterize its distribution and severity.
Action potential: A brief electrical signal that travels along an excitable cell membrane. Muscle electrical recordings arise from action potentials in muscle fibers.
Magnetic resonance imaging: An imaging method that uses magnetic fields and radio waves to create internal body images. MRI depicts muscle structure, whereas EMG measures electrical activity.
Motor unit action potential: The recorded electrical waveform produced by muscle fibers activated by one motor neuron. Its size, shape, and duration help characterize changes in motor units.
Amyotrophic lateral sclerosis: A progressive disease that damages motor neurons controlling voluntary muscles. EMG can reveal widespread denervation and reinnervation in its diagnostic evaluation.

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