SLE2/MODULE 6- Motor Units TECHNIQUES Flashcards
single motor unit refers to
the neuron + its fibers
the force exerted by a muscle depends on ____
the cumulative force that is contributed by the MUs that have been turned on
techniques to study single MU (2)
-intramuscular + subcutaneous electrodes
-spike-triggered averaging (STA)
techniques to study population of MUs (2)
-motor unit number estimation
-high-density grid-electrode arrays
who created the concentric needle electrode
Adrian + Bronk
-1929
who created the fine wire electrode
Bigland + Lippold
-1954
who created the fine wire with insulation removed
Gydkov et al.
-1984
how do electrodes communicate electrical signals
by working in pairs
what was the first intramuscular electrode developed
concentric needle electrode
what is concentric needle electrode made of
insulated copper wiring
-has exposd end
-placed within hydodermic needle
how is concentric needle electrode placed
placed into muscle + held in place with tiny plug
electrodes of concentric needle electrode
needle + wires make up the 2 electrodes
-exposed end of copper wiring projects into opening of needle + forms 1 electrode
-the other electrode is the needle itself
Bigland
the “queen of fatigue research”
what did Bigland + Lippold do
improved the selectivity if what wires could do
-you could select specific MUs you want to track in your research
what is fine wire electrode made of
insulated wires with bare ends that were inserted into a hypodermic needle
-no plug
-wire comes in OTHER end
-the sharp end of the needle has a bend
what made fine wire electrode different
signals recorded with these electrodes (the 2 wires within the needle) were a lot more selective
-highly variable because electrode could move during recording
what are the electrodes of the fine wire electrode
the 2 wires within the needle
fine wire with insulation removed
subcutaneous electrode
-improved upon the previous 2 electrodes (concentric needle + fine wire electrodes)
what is fine wire insulation removed electrode made of
-first wire has 2 recording sites + in between those 2 recording sites, there is 1 recording site on the second wire
-comprised 2 insulated wires
-wires were glued together so they did not move away from each other when placed in the muscle
where are intramuscular electrodes placed
directly into the muscle
where are subcutaneous electrodes placed
right on top of muscle fibers, but below subcutaneous tissue (fat/skin)
benefits of subcutaneous electrodes
not moving as much so not variable recordings
-BUT can only detect APs from superficial muscles because of the placement being right over the muscle
gold standard of electrodes
intramuscular electrodes
-recording is best
-more selective
in Diba’s opinion, which electrode is superior
subcutaneous
-because you can follow MUs across continuous longer term contractions
depending on the electrode, you can record from ____ fibers to ____ fibers belonging to different motor units
-1-3 fibers
-15-20 fibers
motor unit APs typically have what phase
bi or triphasic phase
diameter of electrode wires
50 microns
-the size of human hair
electrode study- what did clicking sound indicate
there is a code that is created so that any time that wave form hits a certain amplitude there is a clicking sound projected through the speaker
what technique can estimate the number of functioning MUs in a muscle
spike-triggered averaging (STA)
spike-triggered averaging (STA)
basically using 1 MU’s function to get an estimate of the other MUs involved + their contributions to net force
-extracts the force contributed by a SINGLE MU to the net muscle force during sustained voluntary contractions
-APs produced by the MU trigger an averaging device that samples the muscle force at that time point
-calculates a running average from many triggered events
what does STA technique do
extracts force developed by 1 motor unit during a sustained voluntary contraction
-we can measure the info from that small intramuscular recording to get an estimate of what the bigger picture of force contribution is
spike-triggered averaging- what color is surface EMG
black
spike-triggered averaging- what color is intramsucular EMG
green
spike-triggered averaging- is it possible to observe the corresponding surface MU potential for any 1 discharge of a MU using a intramuscular EMG
NO
-however it is possible to generate an average of the surface EMG centered around the times of discharge of the MU
spike-triggered averaging- how is the estimate shown
shown for an average generated using 10 discharges of the motor unit, and the estimate improves when 20 discharges are used as trigger events, and then 30, 40, 50, …140
how can twitch force + the time to peak force (contractio time ) be measured in humans
spike-triggered averaging
variations of STA
-researchers have modified STA over the past few years
-there are some variations on how it is applied in different protocols
-some papers use a classical method; others use an updated method
what is the overarching idea of all STA variations
-to evaluate the mechanical activities of single MUs, the STA technique extracts the amount contributed by a single MU to the net muscle activity during sustained voluntary contractions
-the APs produced by the motor unit trigger an averaging device that samples the muscle activity at that particular time point + calculates a running average from many triggered events
-the average is the surface EMG, which is related to the muscle force
limitations of STA
-how do factors that increase and decrease amplitude cancellation influence the size of the potentials extracted from the surface EMG?
-data collection takes about 2-3 minutes – this may confound the twitch profile by twitch potentiation and/or fatigability.
-generally recording units turned on at low forces, or low recruitment thresholds.
MUNE
M wave / mean sMUAP
MUNE technique stands for
motor unit number estimation (MUNE)
MUNE technique
measures the number of motor neurons that innervate a muscle
MUNE
iMUAP
intramuscular
MUNE
sMUAP
surface level
MUNE
how is M wave acquired
by shocking the nerve for the muscle of interest
MUNE
how does M wave change
M wave changes in time + increases until it hits M max (as high or low as it can be)
how do we calculate MUNE
M wave / average of sMUAP
M wave is ____
artifically induced
see slide 22/23 + notes
which of the following statements about the spike-triggered averaging (STA) technique is correct?
a) the trigger event is an electric stimulus applied to the nerve
b) STA can be used to extract an average value from an intracellular EMG recording
c) amplitude is measured in ms
d) the size of the response would be similar for weak and strong motor units
e) the spike is the motor unit action potential
e) the spike is the motor unit action potential
which of these statements about the MUNE technique is incorrect?
a) the size of the response of each motor unit will depend on its innervation number
b) the average amplitude of the motor unit responses is measured in voltage
c) the amplitude of the M wave is always greater than the sum of the recorded motor unit responses
d) the method can record the individual responses of all motor units in the muscle
e) the technique is a reasonable estimate but imperfect
d) the method can record the individual repsonses of all motor units in the muscle
post-poliomyelitis syndrome
a neurological disorder that occurs in individuals who have recovered from paralytic poliomyelitis
-as aging occurs, muscles naturally shrink, but with this disorder, there is severe atrophy of the motor unit besides aging
clinical features of post-poliomyelitis syndrome
-weakness
-fatigue
-pain
normal count for extensor digitorum brevis
~200 with an amplitude of 100 uV
amyotrophic lateral sclerosis (ALS)
degeneration of motor neurons
see slide 30 for graphs
what have these 2 diseases done to this muscle? (depicting post-polio syndrome + ALS)
a) varies across individuals
b) most have fewer motor units
c) most have smaller amplitude potentials
d) will impact force output
e) all of these changes have occurred
e) all of these changes have occurred
high-density grid-electrode arrays
look a MUs over a large surface of muscle
-composed of multiple detection points
-any location where there are 2 dots next to each other is a recording site
-shows it is possible to detect APs of motor units as they propagate
-consider these amped up on steroids of the usual bipolar electrode you would stick onto a muscle
what was used to drive a prosthetic limb
EMG signals produced by REINNERVATED muscle
-targeted reinnervation
there are various methods that can be used to study motor units, recording from either a SINGLE motor unit or MANY motor units within the entire population that innervate a single muscle
methods to study single motor units provide information about either the ELECTRICAL or MECHANICAL OUTPUT by means of intramuscular or subcutaneous electrodes or via the SPIKE-TRIGGERED AVERAGING technique, respectively
methods to study motor unit populations comprise high-density grid- electrode arrays and MOTOR UNIT NUMBER ESTIMATION techniques
*be able to name the techniques
*recognize the labels or parts of each of the technique, what type of info they are getting, how that info is transferred from an analog thing that I am doing as a human being to see on a computer screen
