EMG Flashcards
What does the EMG look like with spontaneous activity?
fibrillation potentials
positive sharp waves
On the EMG reading, above the baseline is considered ______ (pos/neg).
negative
What accounts for spontaneous activity?
acutely denervated muscle fibers have Ach receptors over the whole muscle fiber membrane rather than just at the neuromuscular jxn. This means the fiber is supersensitive and discharges spontaneously.
The wave in spontaneous potentials represents depolarization of ______.
single muscle fibers
NOT whole MUs
At rest, normal muscle is SILENT. What is it called when the EMG picks up sound at rest?
spontaneous potential
AKA fibrillation AKA pwave
Why would insertional activity be prolonged with diseased muscle or enervated muscle?
excessive exchange of ions across muscle membrane with needle stimulation
How can you distinguish fibrillations from fasciculations/?
fasculations are larger and more complex than fibrillation potentials
How can fasciculations can be distinguished from MUs discharging due to poor relaxation?
fasciculations are NOT under voluntary control
What is a fasciculation?
waveform that represents contraction of a group of muscle fibers; arises from discharge of part or all of a single MU
How does a fasciculation appear?
isolated discharges that recur at irregular intervals
How do you distinguish MUAP and fibrillation potentials?
look similar but MUAP are much bigger
What may be absent in complete denervation or reduced in partial denervation?
Interference pattern and MUAP
Positive sharp waves at rest are indicative of
spontaneous conductance
“Dive Bomber” is characteristic of
myotonic discharge
High frequency discharges are characteristic of
myopathies
myotonic dystrophy
At rest, what do you see as nerve recovers and muscle begins to be reinnervated?
increased insertional activity until all muscle fibers are reinnervated
Until all muscle fivers are re-innervated, what will you see?
some fibrillation potentials and positive sharp waves
With minimal contraction, what do you see as muscle fibers begin to reinnervate?
nascent units
What are nascent units?
very small amplitude
short duration
polyphasic potentials
Why are nascent units small and polyphasic?
few muscle fibers in reinnervated MU
asynchronous
terminals conduct at different velocities
What adaptation occurs to assist fibers that where not reinnervated successfully?
collateral sprouting
Describe collateral innervation.
distal terminal ends of preserved MUs sprout and pick up adjacent dennervated muscle fibers
What does collateral innervation produce?
polyphaisc
long duration MUAP
at 6-8 weeks (sooner than nascent units)
What two elements constitute giant motor units?
nascent units
collateral sprouting
Giant motor units may form over a period of ___-___ months.
12-18 months
With reinnervation, what happens to insertional activity?
reduces to normal over time
What happens to MUAP after reinnervation begins?
MUAP gains amplitude and duration with time
As more MUs become reinnervated, what happens to interference pattern?
pattern fills in and gains amplitude
What accounts for interference pattern? (3)
- more units are recruited (larger ones)
- firing frequency increases
- some summation occurs (some units fire simultaneously)
With maximum contraction (normal EMG), what pattern is observed?
full interference pattern
Normal EMG summary: (4)
- minimal insertional activity
- electrical silence at rest
- MUAP bi- or triphasic
- full interference pattern with maximal contraction
MUAP represents?
activity of muscle fibers of a single MU (unit is milliVolts)
can be bi- or triphasic
MUAP amplitude is?
sum of muscle fibers contracting at the same time
The first upward deflection is the activity of what muscle fibers? Later deflections represent what muscle fibers?
fibers closest to electrode first
more distal fiber activity later
What factors influence size, shape, and duration of MUAP? (5)
- distance b/w electrodes
- location of electrodes
- size of electrodes
- size of MU and fiber dispersion
- depth of MU and distance from electrodes
Why is there asynchrony of muscle fiber contractions in MU?
variation of collateral axon length
What occurs with normal EMG insertion?
disruption of muscle membrane
duration up to 30 msec
(some insertional activity is normal)
After insertional activity, there is _______ at rest in normal MUs.
electrical silence
Single MU with minimal effort appears?
3-16msec duration @ 5-15/sec frequency
sound-thumping
bi- or triphasic
EMG evaluates _____ qualities of nerve and muscle.
passive
EMG examines _____ contraction on _____ MU level.
voluntary contraction on single MU level
EMG only examines ____ system.
motor
