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315 Cards in this Set
- Front
- Back
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4 key things to describe in EMG report
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- location
- duration - severity - prognosis |
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What is the basic functional element of the neuromuscular system?
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the motor unit
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What are the 7 components of the motor unit (from proximal to distal)?
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- anterior horn cell
- nerve root - spinal nerve - plexus - peripheral nerve - neuromuscular junction - muscle fiber |
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Where is the alpha-motor neuron located?
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cell body of the motor nerve; located in the anterior horn of the spinal cord
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What regulates the characteristics of the motor unit?
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The alpha motor neuron
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What is the innervation ratio?
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The amount of muscle fibers belonging to an axon
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Do muscles with stronger/grosser movements have a higher or lower innervation ration?
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Higher (more muscle fibers per axon)
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What is the relationship between innervation ratio and force generated by a muscle?
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Higher innervation ratio = greater force
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What is a typical innervation ratio for a muscle in the leg?
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600 muscle fibers : 1 neuron
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What is a typical innervation ratio for a muscle around the eye?
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1 muscle fiber : 1 neuron
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Define the neuromuscular junction
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The location in the motor unit where electrical AP is converted to chemical energy to initiate a a muscle action potential.
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What type/category of motor neurons can can EMG study?
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Alpha motor neurons (Ia fibers)
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What are the 2 general ways that alpha motor neurons are further described?
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- size
- physiology |
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What order are alpha motor neurons recruited?
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In order of the size of the motor unit (smaller muscle fibers first)
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The sequential activation of motor units allowing for smooth increase in contractile force is described by what principle?
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Henneman Size Principle
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Alpha motor neurons innervate ______
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extrafusal fibers (skeletal muscle)
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Gamma motor neurons innervate ______
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intrafusal fibers (muscle spindle)
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Beta motor neurons innervate _____
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intrafusal and extrafusal fibers (skeletal muscle and the muscle spindle)
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What are extrafusal fibers?
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skeletal muscle
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What are intrafusal fibers?
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muscle spindle fibers
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4 basic characteristics of type I muscle fibers
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- smaller cell body
- thinner diameter axon - lower innervation ratio - slower twitch muscle |
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4 basic characteristics of type II muscle fibers
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- larger cell body
- thicker diameter axon - higher innervation ratio - faster twitch muscle |
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What is the Henneman size principle?
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A smaller alpha motor neuron has a lower threshold of excitation causing it to be recruited first. Larger alpha motor neurons have larger thresholds causing them to be recruited when more force is needed.
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What order do the "neurium" layers go in from outside in?
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- epineurium
- perineurium - endoneurium |
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Define endoneurium
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Connective tissue surrounding each individual axon and its myelin sheath
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Define perineurium
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Connective tissue surrounding bundles or fascicles of myelinated and unmyelinated nerve fibers
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What is the purpose of the perineurium?
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- strengthens the nerve
- acts as a diffusion barrier |
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May individual neurons cross from one bundle to another throughout the course of the nerve?
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yes
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Define epineurium
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loose connective tissue surrounding the entire nerve that holds the fascicles together and protects it from compression
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Define resting membrane potential
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the voltage of the axon's cell membrance at rest
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What are "leak channels"?
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Channels that allow K and Na to move passively in and out of the cell membrane
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What is the normal resting membrance potential of an axon?
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-70 to -90mV
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How many K and Na are involved in the K/Na pump?
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3Na out for every K in
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The resting membrane potential is maintained by the
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Na/K pump
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Most important event in generating an action potential is...
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sodium conductance
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How does the stimulator in NCS cause the nerve to depolarize?
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Positive ions accumulate under the negative pole of the stimulator (cathode) and lower the membrane potential. The membrane becomes increasingly permeable to Na ions which eventually rush in through the voltage gated channel and depolarize the membrane (sodium conductance)
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What are the 3 conformations of the voltage gated sodium channel?
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- resting
- activated - inactivated |
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About how long to sodium channels stay open during an action potential?
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about 25 microseconds
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What are the general conceptual effects of cold on the sodium channel?
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channel open and closes later
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Is there a difference in the waveform effects in NCS for focal vs. generalized cooling?
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Yes, generalized cooling has more significant effects in all domains
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Classically, cooling causes an increase in the amplitude of NCS - but sometimes you see a decrease...why?
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- temporal dispersion
- negative phase cancellation |
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What are the general effects of cooling that can be expected with NCS waveform morphology?
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- latency prolonged
- amplitude increased - duration increased - conduction velocity decreased |
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Why does the movement of Na into a channel end up causing a propagating action potential?
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Because the path of least resistance is along the length of the axon (both directions)
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During an action potential when sodium is rushing in - what prevents it from going right back out
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myelin
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The process of propagating a current from one node to another is called
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saltatory conduction
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Define orthodromic
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action potential is monitored traveling in the direction of its typical physiology conduction (usually described as away or toward the spinal cord)
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Define antidromic
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action potential is monitored traveling in the opposite direction of its typical physiology conduction (usually described as away or toward the spinal cord)
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The repolarization phase of an action potential is dependent on
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Na channel inactivation and K channel activation
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What are the 2 conformational phases of the voltage gated K channels?
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- resting
- slow activation |
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What is the "overshoot phenomenon"?
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The hyperpolarization that occurs because of the slow activation of K channels
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What is the motor endplate?
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The distal portions of the motor axon and the muscle fibers that they innervate
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Define the presynaptic region of the neuromuscular junction
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the bulbous area at the axon's terminal zone
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How many storage compartments are there for acetylcholine in the presynaptic region of the axon and how many quanta does each compartment store?
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- main store = 300,000
- mobilized store = 10,000 - immediate store = 1,000 |
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A quata of acetylcholine contains about how many molecules of acetylcholine?
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5,000-10,000 molecules
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How long does the migration of acetylcholine from the axon's main and mobilization compartments to immediate release take?
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4-5 seconds
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Define the synaptic cleft of the region of the neuromuscular junction in a motor neuron
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the regions where acetylcholine crosses from the presynaptic region towards receptors on the postsynaptic region
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How wide is the synaptic cleft of the neuromuscular junction?
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about 200-500 angstroms
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Acetylcholinesterase degrade acetylcholine into...
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Acetate and choline
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The convolutions in the postsynaptic region increase the surface area by how many times
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10
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What are "presynaptic active zones" in the motor neuron?
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Areas on the presynaptic membrane where acetylcholine is released
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The postsynaptic Ach receptor requires __ molecules of Ach to be activated
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2
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During the periods of inactivation in a motor unit, a spontaneous release of Ach quanta occurs every __ seconds
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5
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Spontaneous release of Ach quanta in motor neurons results in ____
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MEPP (miniature endplate potential)
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The calcium associated with depolarization and release of Ach in motor neurons stays in the terminal axon for how long?
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200ms
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Normally, the end-plate potential amplitude is ___ times amount needed to initiate an action potential
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4
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The "safety factor" in an end-plate potential depends on what 2 factors
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- quantal count (numbner of quata released)
- quantal response (ability of receptors to respond) |
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What are the defining edges of the sarcomere?
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Z line to Z line
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During normal muscle contraction the I band and the H zone ____ in size
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decrease
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During maximal muscle contraction the H zone...
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disappears
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Muscle contraction is initiated by
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muscle fiber depolarization
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How quickly does muscle fiber depolarization spread?
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3-5 meters per second
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How can the muscle fiber depolarization penetrate deeper into the muscle?
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T-tubule system (calcium is released from the sarcoplasmic reticulum)
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What is Ohm's law?
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E = IR
Electromotor source (volts) Current (I) amperes Resistance (Ohms) |
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CMAP =
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compound muscle action potential
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SNAP =
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sensory nerve action potential
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What are the limitations of using a needle recording electrode in NCS?
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Because you are only recording a few fibers you can't validly analyze the amplitude or the conduction velocity of the waveform you record with a needle.
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Describe a monopolar electrode. Where is the reference?
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22-30 gauge Teflon coated needle with exposed tip of 0.15-0.2mm
- requires external reference |
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What are the advantages of the monopolar electrode?
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- inexpensive
- conical tip allows for omnidirectional recording - less painful - larger recording area - records more positive sharp waves |
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What is the relative recording area size of monopolar vs. concentric needles?
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monopolars record twice as much field
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What are the disadvantages of monoplar electrodes?
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- requires a separate reference
- unstandardized tip area - Teflon can fray - more interference |
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Describe a concentric electrode. Where is the reference?
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The 24-26 gauze needle serves as the reference, the active is a bare inner wire
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What are the advantages of the concentric electrode?
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- standardized active area
- fixed location from the reference - less interference - no separate reference - can be used for quantitative EMG |
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What are the disadvantages of the concentric electrode?
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- beveled tip = unidirectional recording
- smaller recording are - MUAPs have smaller amplitudes - more painful |
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MUAP =
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motor unit action potentials (what you see on EMG)
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Describe a bipolar concentric electrode
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Has active and reference electrode wires within the needle lumen
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Define ground electrode
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A zero-voltage, neutral, surface reference point placed between the recording electrode and the stimulating electrode
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Define anodal block
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A theoretical local block that occurs when reversing the stimulator's cathode and anode; this hyperpolarizes the nerve, thus inhibiting the production of the action potential.
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Define threshold stimulus
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electrical stimulus occuring at an intensity level just sufficient enough to produce a detectable evoked potential from the nerve
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Define maximal stimulus
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Electrical stimulus at an intensity level where no further increase in evoked potential occurs as a higher stimulus
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Define supramaximal stimulus
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20% above maximal stimulus
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What effect does supramaximal stimulus have on latency?
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Decreased
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What technical NCS error can occur with stimulus duration greater than 0.3ms?
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falsely prolonged distal latency since nerve is stimulated for a longer period of time
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Recommended stimulus duration in NCS
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0.1-0.3ms
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6 sources of environmental electrical noise interference in EMG/NCS
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- EMG audio feedback
- needle artifact - 60Hz interference - preamplifier - fluorescent lights - the patient |
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Signal to noise ratio =
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(signal amplitude) x (square root # averages performed) / noise amplitude
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Stimulus artifact represents
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the current spread across the skin to the electrode
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List 3 ways you can reduce the stimulus artifact
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- ground between the stimulator and recording electrode
- appropriate anode and cathode placement - improving electrode contact by cleaning the skin |
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What does the differential amplifier do?
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- responds to alternating currents
- cancels waveforms recorded at active and reference pickups - amplifies remaining potentials |
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Optimal parameters for a differential amplifier
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- high impedance
- common mode rejection - low noise from within the system |
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What's an acceptable common mode rejection ratio (CMRR)?
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Greater than 90dB
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What does the common mode rejection ratio tell you?
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The larger the CMRR the more efficient the amplifier
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NCS: Differential signal =
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active - reference
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Filters are made of
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resistor and capacitors
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What is the frequency band width in electrodiagnostics?
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The frequencies between the low and high frequency filters that the machine is allowed to see
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What are the typical filter settings for sensory NCS
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20Hz - 2kHz
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What are the typical filter settings for motor NCS
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2Hz-10kHz
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What are the typical filter settings for EMG?
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20Hz-10kHz
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What effects on waveform morphology occur with elevating the low frequency filter
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- shortens peak latency
- reduces the amplitude - potentials go from bi- to triphasic - does not change the onset latency |
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What effects on waveform morphology occur with reducing the high frequency filter
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- prolongs the peak latency
- reduces amplitudes - creates a longer negative spike - prolongs the onset latency |
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What are the x and y axes on the screen display for NCS
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x = sweep speed
y = sensitivity |
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NCS sweep speed is measured in
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ms
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NCS sensitivity is measured in
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mV or uV
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In NCS what are the units of gain?
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no units; it's a measurement of output to input
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Why does demyelination cause problems with saltatory conduction?
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Demyelination increases the membrane capacitance (loss of insulation)
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Define conduction block
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Failure of the action potential to propagate past an area of demyelination along the structurally intact axons
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What are the parameters for defining conduction block on NCS?
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greater than 50% amplitude drop
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Typical NCS findings with demyelination
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- prolonged latency
- decreased amplitude across the site of injury - temporal dispersion - decreased conduction velocity |
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Typical EMG findings with demyelination
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- normal insertional activity
- normal resting activity +/- myokymia - +/- decreased recruitment - MUAP normal |
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What changes with demyelination?
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- shorter internodal distance
- conduction velocity improves but still slower than normal |
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When is Wallerian degeneration complete for motor nerve and sensory nerves?
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- motor complete by 7 days
- sensory complete by 11 days |
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4 general mechanisms of axon injury
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- focal crush
- stretch - transection - peripheral neuropathy |
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Typical NCS findings with axonal injury
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- normal latency
- decreased amplitude in the entire nerve - normal temporal dispersion - decreased conduction velocity |
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Typical EMG findings with axonal injury
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- abnormal insertional activity
- abnormal resting activity - decreased recruitment - abnormal MUAP |
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2 major mechanisms of recovering after axonal injury
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- collateral sprouting
- axonal regrowth |
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How fast will an axon regrow?
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1mm/day; 1 inch/month
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What are nascent potentials?
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motor units after axonal regrowth that have low amplitude, long duration and are polyphasic
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What is the Seddon classification?
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Seddon classification of nerve injury:
- neuropraxia (compression) - axonotmesis (crush) - neurotmesis (transection) |
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What is the Sunderland classification?
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Sunderland classification of nerve injury:
Type 1: conduction block (neuropraxia) Type 2: axonal injury (axonotmesis) Type 3: type 2 + endoneurium injury Type 4: type 3 + perineurium injury Type 5: type 4 + epineurium injury (neurotmesis) |
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A recorded potential on NCS is made up of
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multiple sinusoidal waves
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Frequency in NCS is measured in
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Hz
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Define onset latency
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The time required for an electrical stimulus to initiate an evoked potential
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Define latency of activation
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The time between initiation of the electical stimulus and the beginning of saltatory conduction
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Typical duration of latency of activation
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0.1ms or less
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Typical time for synaptic transmission
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0.2-1.0ms
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Onset latency in NCS represents
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Conduction along the fastest axons
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Define how you measure onset latency
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Initial deflection from baseline
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Peak latncy in NCS represents
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conduction along the majority of axons
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General parameters for normal conduction velocities in the upper and lower limbs
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- upper 50 m/s
- lower 40 m/s |
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How can conduction velocities be normal even with a lot of axon loss?
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Intact transmission in the fastest fibers
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General guidelines for conduction velocities in children
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- newborns: 50% of adults
- 1 year old: 80% of adults - 3-5 years: equal to adults |
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General guidelines for how nerve conduction decreased witha ge
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Decreased 1.5% per year after age 60 years
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What does amptliude reflect in NCS (generally)
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The number of nerve fibers activated and their synchrony of firing
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What does temporal dispersion in NCS tell you?
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The range in conduction velocities of the fastest and slowest axons (usually seen better with proximal stimulation)
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An amplitude drop of up to ___ is considered normal for proximal SNAPs
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50%
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Why is there so much amplitude drop with proximal SNAP stimultion?
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Phase cancellation; more pronounced with short duration SNAPs
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Expected ampltiude drop in proximal stimulation for CMAPs
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About 15%
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Location of the dorsal root ganglion
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In the neural foramen
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Which is more sensitive in detecting an incomplete peripheral nerve injury, SNAPs or CMAPs?
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SNAPs
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Features of antidromic sensory studies
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- easier to records than orthodromic
- require less stimulation than ortho - hae larger ampltiudes than ortho (nerves are more superficial distally) |
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For SNAPs the active and recording electrodes should be at least ___ cm apart
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4
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How does waveform morphology change when the active and reference electrodes are less than 4cm apart?
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- peak latency decreases
- onset latency about the same - amplitude decreases - duration decreases - rise time deceases |
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Why can't motor NCS localize pre- vs post-ganglionic lesions?
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Because the cell body is in the spinal cord
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List 2 reasons to have a nerve with normal SNAPs but abnormal CMAPs on NCS
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- motor lesion proximal to the DRG
- lesion of only the motor fibers |
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What is the general normal waveform appearance for CMAPs?
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- biphasic
- initial negative deflection |
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3 major reasons to see an initial positive deflection on CMAP waveform
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- active electrode not over motor point
- volume conduction from other muscles/nerves - anomalous innervation |
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What amplitude measure do you use for SNAPs
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peak to peak
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What amplitude measure do you use for CMAPs
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baseline to peak
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The H-reflex is an electrically evoked analogue to a ______
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monosynaptic reflex
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What kind of stimulus do you use for H-reflex?
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submaximal with long duration (0.5ms-1.0ms)
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What do you us a submaximal long duration stimulus for H-reflex studies?
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This preferentially activates the IA afferent fibers
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What kind of responses are involved in the H-reflex?
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orthodromic sensory response to the spinal cord and an orthodromic motor response back to the recording electrode
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How can you facilitate the H-reflex?
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agonist muscle contraction
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How can you abolish the H-reflex?
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- Antagonist muscle contraction
- Supramaximal stimulation that causes "blocking" |
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Are the morphology and latency of H-reflex waveforms constant or variable?
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constant at the appropriate stimulus
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What is the "formula" for H-reflex?
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= 9.14 +0.46 (leg length in cm from the medial malleolus to the popliteal fossa) +0.1 (age)
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What is the generally normal latency for H-reflex? side to side difference? changes with age?
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- latency: 28-30ms
- side to side difference: greater than 1-2 ms - above 60 years: add 1.8ms |
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Trace the fibers traveled for the H-reflex
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1A afferent --> synapse in spinal cord to --> alpha motor neuron
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What are the 2 muscles typically studied with H-reflexes?
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- gastrosoleus (tibial motor, S1)
- flexor carpi radialis (median motor, C6-7 pathway) |
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In what groups of patients can H-reflexes be obtained in almost any muscle group?
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- infants
- adults with UMN corticopinal tract lesions |
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List some common limitations of the H-reflex
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- evaluates a long pathway which can dilute focal effects
- can be normal with incomplete lesions - does not distinguish between acute and chronic lesions - once abnormal, always abnormal |
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What stimulation level do you use for F-waves?
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supramaximal
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What is the general pathway for an f-wave?
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antidromic motor to the spinal cord with orthrodromic motor return
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What is the approximately amplitude of an f-wave compared to the CMAP?
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5%
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Is the f-wave latency constant or variable? why?
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variable. It's a polysynaptic response where renshaw cells can have an inhibitory effect
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Normal UE latency for f-waves
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28msec
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Normal LE latency for f-waves
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56msec
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What is the significant side-to-side difference for f-waves?
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2.0msec in UE, 4.0msec in LE
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Limitations of the f-wave
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- evaluates a long pathway which can dilute focal lesions
- only assess motor fibers |
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What happens to a-waves with supramaximal stimulation?
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They disappear
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General location of an a-wave on a trace
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Between with CMAP and the f-wave at a constant latency
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what does an a-wave represent?
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Usually collateral sprouting
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On NCS the blink reflex is likely what reflex on physical exam?
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the corneal reflex
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What nerves are tested in the blink reflex in NCS?
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V and VII
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Trace the pathway being tested during the blink reflex
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sensory of superorbital branch of trigeminal nerve (VI) --> pons --> lateral medulla --> facial nerve (VII) --> bilateral orbicularis oculi
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The R1 response in the blink reflex NCS represents a pathway through the
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pons
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The R2 response in the blink reflex NCS represents a pathway through the
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pons and lateral medulla
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The R1 response in the blink reflex NCS is affected by lesions of the...
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- trigeminal nerve
- pons - facial nerve |
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The R2 response in the blink reflex NCS is affected by lesions of the...
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- consciousness level
- Parkinson's disease - lateral medullary syndrome - contralateral hemisphere - valium - habituation |
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What are the normal latency measurements for the blink reflex?
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R1 < 13 msec
R2 ispilateral <40 msec R2 contralateral <41msec |
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Where do you stimulate and record for a facial nerve NCS?
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- stim distal to the stylomastoid foramen at the angle of the mandible
- record over nasalis |
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Common manifestations of synkinesis after facial nerve injury
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- lip twitching when closing the eye
- eye closure when smiling - crocodile tears when chewing |
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Give some of the more common underlying causes of a facial nerve lesion
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- bell's palsy
- neoplasms - fractures - middle ear infections - DM - Lyme disease |
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If you want to follow-up facial NCS to look at prognosis, how far apart should the studies be?
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OK to f/u every 2 weeks or so
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How can you use evoked potentials of the facial nerve to predict prognosis?
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Absence of evoke potentials at 7 days indicate poor prognosis
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Describe facial nerve recovery prognosis based on CMAP amplitude
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- less than 10% of unaffected side = poor (recovery often greater than 1 year and likely incomplete)
- 10-30% of unaffected side = fair (recovery within 2-8 months) - >30% unaffected side = good (recovery within 2 months) |
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Common interventions to try for facial nerve palsy
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- prednisone
- massage - estim |
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What path in the spinal cord does SSEP test?
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posterior columns
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Trace the ascending pathway for SSEPs
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peripheral nerve --> plexus --> root --> spinal cord (posterior column)--> contralateral medial lemniscus --> thalamus --> somatosensory cortex
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What level of stimulus is used for SSEPs?
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repetitive submaximal stim
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In general, how are SSEPs utilized for surgical monitoring during lumbar spine surgery
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if tibial signals are lost and median signals stay intact it is concerning for injury during spine surgery
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List the N_ labels / recording sites commonly used for SSEP with median nerve stimulation
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- N9: Erb's point
- N11: Roots - N13: Cervical medullary junction - N20: Cortical |
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List the N_ labels / recording sites commonly used for SSEP with tibial nerve stimulation
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- PF - popliteal fossa
- L3 - 3rd lumbar - N22: T12 / lumbosacral spine - N45: cortical |
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What sensation travels in the dorsal columns?
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- vibration
- proprioception |
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List major limitations of SSEPs
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- only tests dorsal columns
- evals a long pathway and may dilute focal lesions - adversely affected by sleep, high dose general anesthetics |
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Normal insertional activity on needle EMG is
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300ms
|
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2 main causes of increased insertional activity on needle EMG
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- denervaion
- irritable cell membrane |
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4 main causes of decreased insertional activity on needle EMG
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- fat
- fibrosis - edema - electrolyte abnormalities |
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End plate potentials on needle EMG represent
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single fiber action potentials
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Spontaneous quanta release at the NMJ occur about every __ seconds
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5
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What causes a miniature endplate potential (MEPP) on needle EMG?
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spontaneous release of Ach quanta
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Describe the appearance of MEPPs on needle EMG
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10-50uV non-propagated potential - generally appears as an irregular baseline
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MEPPs are usually ____-phasic
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mono
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EPPs are usually ___-phasic
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biphasic
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Typical duration of a MEPP
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0.5-1.0ms
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Typical duration of an EPP
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2.0-4.0ms
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Typical amplitude of a MEPP
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10-50uV
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Typical amplitude of an EPP
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less than 1mV
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Typical rate of firing of MEPP
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150Hz
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Typical rate of firing of EPP
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50-100Hz
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Firing rhythm of a MEPP
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irregular
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Firing rhythm of an EPP
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irregular
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Origin of the MEPP
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endplate
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Origin of the EPP
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enplate/provoked with mechanical depolarization
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Typical sound of a MEPP
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Sea shell murmur
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Typical sound of an EPP
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sputtering fat in a frying pan
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What is the underlying pathophysiology of a fibrillation?
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denervated single muscle fibers from uncontrolled ACh release
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Firing rhythm of fibrillations
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regular
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Why don't positive sharp waves have a negative phase?
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because they are propagated to but not beyond the needle tip
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The initial deflection of a fib is
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positive
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The initial deflection of a PSW is
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positive
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Typical duration of a fib is
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1-5ms
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Typical duration of a PSW
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10-30ms
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Typical amplitude of fib
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early is greater than 300uV and late is less than 25uV
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Typical amplitude of PSW
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less than 1mV
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Typical rate of firing of a fib
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1-10Hz
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Typical rate of firing of a PSW
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1-20 Hz
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Firing rhythm of a fib
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regular
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Firing rhythm of a PSW
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regular
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Is the origin of the fib pre- or post-unctional?
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postjunctional
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Is the origin of the PSW pre- or post-unctional?
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postjunctional
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Typical sound description of a fib
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rain on a tin roof
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Typical sound description of a PSW
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dull thud or chug
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Define 0 fibs/PSW
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none
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Define 1+ fibs/PSW
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Persistent single runs >1 second in 2 areas
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Define 2+ fibs/PSW
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Moderate runs greater than 1 second in three or more areas
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Define 3+ fibs/PSW
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Many discharges in most muscle regions
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Define 4+ fibs/PSW
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Continuous discharges in all areas of the muscle
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How are complex regional discharges (CRDs) generated?
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AP generated from a single pacemaker that causes a group of single muscle fibers to fire in synchrony
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Typical amplitude of a CRD
|
50-10000uV
|
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Typical rate of firing of a CRD
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10-100Hz
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Typical rhythm of firing of a CRD
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Regular spurts with abrupt starts and stops
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Origin of a CRD
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postjunctionall/ephaptic transmission
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Typical sound description of a CRD
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motor boat
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Classic causes of CRDs
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- anterior horn cell diseases
- chronic radiculopathy - peripheral neuropathy - polymyositis - dermatolmyositis - musclar dystrophy - limb girdle dystrophy - myxedema * can be normal variant |
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Typical duration of a myotonic discharge
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5-20 ms
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Typical amplitude of a myotonic discharge
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20-300uV
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Typical rate of firing of a myotonic discharge
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20-100Hz
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Typical rhythm of a myotonic discharges
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wax and wane
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Origin of a myotonic discharge
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postjunctional
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Typical sound of a myotonic discharge
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dive bomber
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Classic diseases where myotonic discharges are found
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- chronic radiculopathy
- peripheral neuropathy - myotonic dystrophy - myotonia congenita - paramyotonia - polymyositis - dermatolmyositis - maltase deficiency - hyperkalemic periodic parlysis - propranolol |
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Hallmark sign of a fasciculation
|
irregularly firing motor unit
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Typical duration of a fasciculation
|
5-15ms
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Typical amplitude of a fasciculation
|
less than 300uV
|
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Typical rate of a fasciculation
|
0.1-10Hz
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Typical rhythm of a fasciculation
|
irregular
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Origin of a fasciculation
|
prejunctional
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Describe grade 0 fasciculation
|
none
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Describe grade 1+ fasciculation
|
In 2 areas, 2-10/min
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Describe grade 2+ fasciculation
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In many areas, 10-15/min
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Describe grade 3+ fasciculation
|
All areas, < 60/min
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Describe grade 4+ fasciculation
|
All areas >60/min
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What are myokymic discharges?
|
groups of MUAPs firing repeatedly
|
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Typical amplitude of myokymic discharges
|
100uV to 2mV
|
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Typical rate of myokymic discharges
|
discharge 40-60Hz, interdischarge 0.1-10Hz
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Typical rhythm of myokymic discharges
|
semiregular
|
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Origin of myokymic discharges
|
prejunctional
|
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Typical sound of myokymic discharges
|
marching soldiers
|
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Typical causes of facial myokymia
|
MS, brainstem neoplasms, polyradiculpathy, Bell's palsy
|
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Typical causes of myokymia in the extremities
|
radiation plexopathy, compression neuropathy, rattlesnake venom
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When are neuromyotonic discharges classically seen?
|
neuromyotonia (Isaac's syndrome)
|
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Why do neuromyotonic discharges taper off at the end?
|
because the single muscle fiber firing fatigues
|
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Duration of neuromyotonic discharges
|
variable can be continuous or in bursts
|
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Characteristic amplitude of neuromyotonic discharges
|
progressive decrement
|
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Typical rate of neuromyotonic discharges
|
100-300Hz
|
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Typical sound of neuromyotonic discharges
|
Ping or motorcycle
|
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Waveform appearance of a neuromyotonic discharges
|
tornado
|
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Typical duration of a cramp discharge
|
gradual start and stop
|
|
|
Typical amplitude of a cramp discharge
|
up to 1mV
|
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Typical rate of cramp discharge
|
40-150Hz
|
|
|
Typical rhythm of cramp discharge
|
irregular
|
|
|
Causes of cramp discharge on EMG
|
- salt depletion
- uremia - pregnancy - myxedema - prolonged muscle contraction - myotonia congenita - myotonic dystrophy - stiff-man's syndrome |
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|
What's the difference between "noise" in an EMG study and artifact potentials?
|
noise is external to the system, artifact potentials are internal to the system
|
|
|
What's a MUAP?
|
An action potential from muscle fibers belonging to a single motor unit within the recording range of the electrode (5-15mm)
|
|
|
Normal amplitude of a MUAP
|
1mV
|
|
|
What does the rise time represent?
|
The proximity of the needle to a motor unit
|
|
|
What's normal rise time for motor unit on needle EMG?
|
less than 500us
|
|
|
Normal MUAP duration
|
5-15ms
|
|
|
Turns on MUAP are also called
|
serrations
|
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How do you calculate the phasicity of a MUAP?
|
baseline crossing plus 1
|
|
|
How do you define polyphasicity in a motor unit?
|
more than 5 crossing the baseline
|
|
|
What % of normal adults have polyphasic motor units?
|
- concentric = 15%
- monopolar = 30% |
|
|
When are doublet/multiplet potentials seen?
|
- ischemia
- hyperventilation - tetany - motor neuron diseases - metabolic diseases |
|
|
What amplitude is considered a "giant" potential?
|
greater than 5mV
|
|
|
What is the "rule of 5s" for motor units?
|
Tend to recruit a new motor unit in every 5Hz of firing
|
|
|
Describe "early recruitment" on EMG
|
many motor units start firing early with activation (hard to fire just one unit)
|
|
|
Describe "decreased" recruitment on EMG
|
One unit firing fast, unable to bring in additional units
|
|
|
What is the recruitment frequency?
|
The firing rate of the first motor unit when the second unit starts to fire
|
|
|
What's a normal recruitment frequency?
|
Less than 20
|
|
|
Recruitment frequency greater than 20 typical reflects...
|
Neuropathic process
|
|
|
What is a recruitment interval on EMG?
|
the interspike interval (in ms) between two discharges of the same MUAP when a second MUAP begins to fire
|
|
|
What's a normal recruitment interval?
|
100ms
|
|
|
How do you calculate recruitment ratio on EMG?
|
Firing rate of 1st MUAP / # MUAP
|
|
|
What's a normal recruitment ratio?
|
Les sthan 10
|
|
|
What's an interference pattern on EMG?
|
the electrical activity recorded from a muscle during maximum voluntary contraction
|
