3 EMG electrodes
Reference, ground, recording
Which electrodes are typically used in
a) small animals
b) large animals
a) concentric
b) monopolar (sharper edge, less painful, more noise, less precise)
Where do we place the ground electrode for:
a) Pelvic limbs
b) Thoracic limbs
c) head
a) Stifle
b) Olecranon
c) occipital protuberance
Negative deflection =
upward
Name the normal EMG pattenrs
Electrically silent
Insertional activity
Miniature end-plate potentials (mEPPs)
End plate potentials/spikes (EPPs)
Motor unit action potentials (MUAPs)
Name the abnormal EMG pattenrs
Fibrillation potentials
Positive sharp waves
Complex repetitive discharges (CRDs)
Myotonic potential
Insertional activity
1. Morphology
2. Cause (physiologic)
3. ↑ in ____
4. ↓ in ____
- Abrupt start/stop, high frequency, crisp static sound
- Dysruption of myofibers by needle insertion or movement
- Denervation or myopathies
- Fibrosis or atrophy
Slide 35
Insertional activity
Start increasing at day ____ and peak at day ____ after denervation injury
4, 8
mEPP
1. Morphology
2. Cause
3. Cease after ____
4. ↓ Frequency with ____
5. ↓ Amplitude with ____
- Small amplitude (5-50 uV), high frequency (5-50 Hz), background activity, 1-2 ms duration, sheashell sound
- Spontaneous post-synptic depolarizations (not AP!) due to random ACh quanta release
- Denervation
- Botulism
- MG
Slide 40
EPP/EPS
1. Morphology.
2. How to distinguish from FPs?
3. Cause
- Biphasic, starting with negative (upward) deflection. Often in association with mEPPs, but larger amplitude
- =
- EPPs = initial upward (negative), often associated with mEPPs.
- FP = initial downward (+), often associated with PSWs. - Normal spontaneous APs (vs mEPPs = depolarizations) of muscle fibers
Slide 42
MUAPs
a) Morphology
b) Cause
a) Biphasic or triphasic, initial -ve deflection, consistent morphology over time. Large amplitude (depends on motor unit density).
b) depolarization of an entire motor unit triggered by voluntary movements
Slide 45
Name the 2 MUAP patterns expected in healthy muscles with increasing muscle contraction strenght
- Recruitment pattern: successive activation of additional motor units with increasing strength of voluntary muscle contractions
- Interference pattern: overlap of multiple MUAPs which precludes individual MUAP recognition at MAX contraction
Expected MUAP responses at MAX muscle contration for…
a) Healthy muscles
b) Neuropathy
c) Myopathy
SEE TABLE SLIDE 50
a) Complete interference pattern
b) Incomplete interference pattern
c) Lower amplitude (yet complete interference)
Fibrillation potentials
1. Morphology
2. Cause
3. Peak ____ days after ____
- biphasic, ~EPPs but initial deflection is +ve (downward). Sound like fried eggs.
- AP from a single, denervated myofiber (occ after needle movement)
- 8 days after denervation (with insertional activity)
Pense au F en italique. Slide 52
Positive sharp waves
1. Morphology
2. Cause
- +ve spike followed by small slow -ve wave. Sound deeper than FPs.
- AP from single, denervated myofiber (some argue that they are the same as FPs but different needle position relative to AP)
Complex repetitive discharges (CRD)
1. Morphology
2. Cause
- Repetitive, polyphasic, uniform, large amplitude, sound like machine gun
- GROUP of myofibers firing in synchrony, following CHRONIC denervation. Due to EPHAPTIC spread.
Slide 60
Myotonic potentials
1. Morphology
2. Cause
- Wax-waning amplitude and frequency. Either runs of waves resembling PSWs or FPs. Smaller amplitude than CRD.
- Repetitive AP from a single myofiber (vs CRD).
