Nerve Conduction and Electromyography Flashcards
What is NCS and EMG used for
We measure mostly the PERIPHERAL NERVOUS SYSTEM. As such, this test is not designed to test central nervous system disorders. We test for disorders of the motor neuron and nervous system structures distal to this structure.
Examples of diseases that can be diagnosed with NCS and EMG
Motor neuron disorder
Motor neuron disorder: lower motor neuron dysfunction in diseases such as polio, amyotrophic lateral sclerosis (ALS), spinal muscular atrophy.
Examples of diseases that can be diagnosed with NCS and EMG
Nerve roots
Nerve roots (sensory and motor): cervical and lumbosacral radiculopathy, nerve root avulsion in trauma.
Examples of diseases that can be diagnosed with NCS and EMG
DRG
Dorsal root ganglia: ganglionopathy/neuronopathy (mostly asymmetric sensory deficits due to damage of dorsal root ganglia).
Examples of diseases that can be diagnosed with NCS and EMG
Brachial and Lumbosacral plexus
Brachial and lumbosacral plexus: due to trauma, inflammatory conditions, infections, neoplastic, related to prior radiation. Think of “Parsonage Turner Syndrome”, “Neuralgic Amyotrophy”, trauma, CMV (Cytomegalovirus lumbosacral polyradiculopathy), Lyme disease.
Examples of diseases that can be diagnosed with NCS and EMG
Peripheral Nerve
Peripheral Nerve: sensory/motor/sensorimotor nerves, symmetric/asymmetric mono or poly- neuropathies, axonal or demyelinating. The most common cause of neuropathy in USA is diabetes, the most common cause of neuropathy worldwide is leprosy.
Examples of diseases that can be diagnosed with NCS and EMG
NMJ
Neuromuscular Junction (NMJ): presynaptic like Lambert Eaton Syndrome and botulism, postsynaptic like Myasthenia Gravis (MG).
Examples of diseases that can be diagnosed with NCS and EMG
Muscle Disorder
Muscle disorders: myopathy with and without membrane irritability, including inflammatory and toxic myopathies.
Examples of diseases that can be diagnosed with NCS and EMG
Cranial nerves
Cranial Nerves: trigeminal nerve, facial nerve, spinal accessory nerve (trapezius, also innervated by ventral rami of C3 and C4 AND sternocleidomastoid), hypoglossal nerve (tongue).
Spinal nerve divisions
Dorsal ramus: skin and paraspinal nerves.
Ventral ramus:
Brachial plexus: C5-T1,
Intercostal nerves: mostly thoracic,
Lumbosacral plexus and pudendal plexus: L1-L5, S1-S4, coccygeal nerve +/- T12.
Brachial plexus
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The brachial plexus is responsible for cutaneous and muscular innervation of the entire upper limb, with two exceptions: the trapezius muscle innervated by the spinal accessory nerve (CN XI) and an area of skin near the axilla innervated by the intercostobrachial nerve.
Brachial plexus
Divided into…
and an area of skin near the axilla innervated by the intercostobrachial nerve. The brachial plexus is divided into Roots, Trunks, Divisions, Cords, and Branches. There are five “terminal” branches and numerous other “pre-terminal” or “collateral” branches that leave the plexus at various points along its length.
Review the brachial plexus
Do it
Mnemonics for remembering the order of brachial plexus
Real Texans Drink Cold Beer
Read The Darn Cadaver Book
Real Teachers Drink Chilled Beer
Randy Travis Drinks Cold Beer
Neurophysiological basis of measuring nerve conduction/EMG
We measure the Extracellular action potentials of the various sensory, motor and muscle fibers. Routine nerve conductions measure large diameter fibers (small nerve fibers can be tested with other special testing, like QSART: Quantitative Sudomotor Axon Reflex Test)
The extracellular action potentials can be measured mostly because of the Na+/K+ pump, which is electrogenic. All the signals that we obtained are the result of the summation of individual cell signals.