7/21/2019 Lab Report Y.docx http://slidepdf.com/reader/full/lab-report-ydocx 1/14 MEDSCI 206 – Laboratory 2 “Human nerve conduction velocity”William Lin 6737564 Date: 17 th August 2015Experiment: Human nerve conduction velocity measurements Condu cted by : William Lin, Samuel Yu, Gagan Joshi, Kelly Cudmore (A7)Aims: Part 1 - Record, and interpret EMG as from a range of voluntary contractions (FDM) - Measure and calculate conduction velocities for ulnar and median nerve by measuring Compound muscle action potential at sites (FDM and APL respectively) as well as stimulating at respective sitesPart 2 - Analyse and interpret both normal and abnormal nerve conduction measurements and thereby proposing potential neuropathies. Introduction: In mature mammals, extrafusal muscles are innervated by single alpha-motor neurons (lower motor neurons). Because the number of available neuronal axons are in large deficit compared to the muscular tissue present in the body, neurons often branch-out to form multiple synaptic connection with muscle fibres to attain a large surface area for electrical stimulation (Purves, 2008). The term “Motor unit” defines both the alpha motor neurons that forms the neuromuscular junction (via its axon terminal) as well as the muscle fibres which that particular neuron innervates (Purves, 2008). In the human body, there are various classes of motor unit, ranging from S (Slow) motor units, FF (Fast-fatigable) motor units and an intermediate class known as FR (Fast-fatigue resistant) motor units(Purves, 2008). Neurons, otherwise also known as Nerve cells, are specialized tissue which act as the electrical wiring of the body, its ability to conduct electrical signal allows for it to propagate and transmit information from the higher centres to the lower target organs (Purves, 2008). The lower motor neurons (alpha-motor) which forms the neuromuscular junction with muscle fibres are modulated through synaptic interaction (at the level of the ventral horn) with upper motor neurons which project from the cerebral cortex etc. (Purves, 2008). The two nerves which are focused on in the laboratory session are the ulnar nerve and the Median nerve which all derive from branches of the brachial plexus (Martini, Timmons & Tallitsch, 2012). The ulnar nerve originates as one of the major nerve divisions from the medial cord and contributes in both sensory and motor functions. The median nerve like the ulnar nerve, also serves in both sensory and motor functions and is formed from collectively the musculocutaneous nerve and the medial cord(Martini, Timmons & Tallitsch, 2012). When a neurone is stimulated by some form of electrical activity, it results in a membrane depolarization which leads to an influx of Ca2+ ions via voltage-gated calcium channels. This influx of calcium ions, causes vesicles containing the neurotransmitter ACh to dock with proteins that primes its fusion. Once the vesicles fuse, its contents are released into the synaptic cleft where it binds to the nicotinic receptors at the post-synaptic density which causes an excitatory end-plate current. (Boron & Boulpaep, 2012) Similar to neurones, muscle fibres also have the ability to conduct electrical signal in order to
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
MEDSCI 206 – Laboratory 2 “Human nerve conduction velocity” William Lin 6737564
Date: 17th August 2015
Experiment: Human nerve conduction velocity measurements
Conducted by : William Lin, Samuel Yu, Gagan Joshi, Kelly Cudmore (A7)
Aims:
Part 1
- Record, and interpret EMG as from a range of voluntary contractions (FDM)
- Measure and calculate conduction velocities for ulnar and median nerve by measuring
Compound muscle action potential at sites (FDM and APL respectively) as well as
stimulating at respective sites
Part 2
- Analyse and interpret both normal and abnormal nerve conduction measurements andthereby proposing potential neuropathies.
Introduction:
In mature mammals, extrafusal muscles are innervated by single alpha-motor neurons (lower
motor neurons). Because the number of available neuronal axons are in large deficit
compared to the muscular tissue present in the body, neurons often branch-out to form
multiple synaptic connection with muscle fibres to attain a large surface area for electrical
stimulation (Purves, 2008). The term “Motor unit” defines both the alpha motor neurons that
forms the neuromuscular junction (via its axon terminal) as well as the muscle fibres which
that particular neuron innervates (Purves, 2008). In the human body, there are various classesof motor unit, ranging from S (Slow) motor units, FF (Fast-fatigable) motor units and an
intermediate class known as FR (Fast-fatigue resistant) motor units (Purves, 2008).
Neurons, otherwise also known as Nerve cells, are specialized tissue which act as the
electrical wiring of the body, its ability to conduct electrical signal allows for it to propagate
and transmit information from the higher centres to the lower target organs (Purves, 2008).
The lower motor neurons (alpha-motor) which forms the neuromuscular junction with muscle
fibres are modulated through synaptic interaction (at the level of the ventral horn) with upper
motor neurons which project from the cerebral cortex etc. (Purves, 2008). The two nerves
which are focused on in the laboratory session are the ulnar nerve and the Median nerve
which all derive from branches of the brachial plexus (Martini, Timmons & Tallitsch, 2012).The ulnar nerve originates as one of the major nerve divisions from the medial cord and
contributes in both sensory and motor functions. The median nerve like the ulnar nerve, also
serves in both sensory and motor functions and is formed from collectively the
musculocutaneous nerve and the medial cord (Martini, Timmons & Tallitsch, 2012). When a
neurone is stimulated by some form of electrical activity, it results in a membrane
depolarization which leads to an influx of Ca2+ ions via voltage-gated calcium channels.
This influx of calcium ions, causes vesicles containing the neurotransmitter ACh to dock with
proteins that primes its fusion. Once the vesicles fuse, its contents are released into the
synaptic cleft where it binds to the nicotinic receptors at the post-synaptic density which
causes an excitatory end-plate current. (Boron & Boulpaep, 2012)
Similar to neurones, muscle fibres also have the ability to conduct electrical signal in order to
MEDSCI 206 – Laboratory 2 “Human nerve conduction velocity” William Lin 6737564
produce fine and coordinated contractions. As a result, electrical current that is generated by a
group of muscle fibres will propagate through the fluid-filled tissue and captured at the
surface of the skin by recording electrodes; this method which electrical activity of voluntary
contraction is known as EMG (Electromyography) (Reaz, Hussain & Mohd-Yasin, 2006).
EMG implements a non-invasive method because electrodes are placed at the level of the
skin and records a composite of electrical activity generated by motor pools. CMAP, whichstands for compound muscle action potential is a compound electrical signal produced by
muscles when recruited via electrical stimulation (neuronal or external). Because it measures
action potential across a motor neuron pool, it is a “graded response” rather than an
individual motor unit which produces a “all or none response” (The Compound Action
Potential (CAP) Of the Frog’s Sciatic Nerve, 2005).
On a clinical level, CMAP and EMG’s are often coupled to produce a more three-
dimensional perspective on the nature of the neuropathy as well as to distinguish a severity
and type of disorder. Comprehensive interpretation of the data allows one to localize the
nature of the neuropathology i.e. Non-focal lesion or Focal lesion and allows for betterdiagnosis for pathological events e.g. Carpal Tunnel Syndrome (Hopkinsmedicine.org, 2015).
Those CMAP measurements allow for conduction velocity to be calculated, it is often
affected by personal factors as well as anthropometric factors such as age, sex, height etc.
(Stetson, Albers, Silverstein & Wolfe, 1992)
Methods
1A.
-Set up the DS7 Stimulator (as shown in page 41 of Laboratory manual). It should be advisedthat if the red fault light comes, please notify experienced personnel e.g. Demonstrator or
Technician
-To locate the digiti minimi muscle, place load down on to subject’s little finger (5 th digit)
and ask him/her to contract against this load. Once the muscle belly had been located, clean
the region of the digiti minimi muscle with alcohol and rub it gently with the sand paper
provided
-Make the following electrode placements as per below: (Ref. Diagram in page 43)
- Active (negative) electrode to be placed over the FDM muscle (lateral-ventral side near the
funny bone region)
- Reference (positive) electrode to be placed distally to the 5th metacarpal-phalangeal joints
on the anterior side of the subject’s little finger (5th
digit)- Ground electrode to be placed on the back of the subject’s hand above the region of the
wrist-joint
-In a fixed time frame of 10 seconds (as calibrated per page 41), the is asked to perform a
gradual progression of muscular actions starting from resting and then to minimal, moderate
and sustained maximal contraction.
-It is advised that data should be saved prior to moving on to the next part (1B)
1B.
-LabChart settings were readjusted to that described in page 44
-The Ground and reference electrode placements were kept as per part 1A, however there isan addition of stimulation electrode which is held by either the subject or other group
MEDSCI 206 – Laboratory 2 “Human nerve conduction velocity” William Lin 6737564
Figure 1A. EMG of different levels of voluntary contraction of the flexor digiti minimi (FDM) – (Group A6, 2015)
Figure 1. Shows a range of voluntary contractions that were made over the course of 10 seconds. When the Muscle (FDM) is
in its resting (basal) tone, there is very minimal fluctuation in amplitude signals; as the tone of muscle activity is increased
(from Minimal to Maximal) there is an evident increase in amplitude (~ 1mV at Minimal contraction compared to ~ 4mV atmaximal contraction) accompanied with an increased frequency of the spikes.
Figure 2. CMAP of Ulnar nerve with varying stimulus parameters (mA) at the Elbow Joint
Figure 2 shows a graded response in terms of the CMAP of the Ulnar nerve when stimulated at increasing stimuli parameters.
A pre-trigger of 10 ms was used and the CMAP of the Ulnar nerve was recorded for a fixed duration of 50 ms. First CMAP
was recorded at 23 mA (Threshold stimulus); Sub-threshold stimuli (5,10,15 mA) did not achieve an recorded CMAP. Evident
from the figure, an increase in stimulus protocol achieved graded increase in CMAP response until 75 mA (Supramaximal) to
which no further stimuli provided additional deflection
MEDSCI 206 – Laboratory 2 “Human nerve conduction velocity” William Lin 6737564
V o l t a g e ( m V )
Figure 4. CMAP of median nerve with varying stimulus parameters (mA) at the Elbow Joint
igure 4 shows a graded response with increasing current stimulation at the median nerve at the level of the Elbow joint. Similar to
igure 2, a 10 ms delay was implemented; the CMAP signal was measured over a period of 50 ms. Sub-threshold stimulus (5 mA –
0 mA) produced no visible signal on the LabChart programme. Stimulus parameters were made in 5 mA intervals, and thehreshold stimulus was identified at 45 mA. From 45 mA, a graded increase is evident until 90 mA (Supramaximal stimulus) to
which further stimuli produced no further increase in the CMAP signal
MEDSCI 206 – Laboratory 2 “Human nerve conduction velocity” William Lin 6737564
Discussion:
Muscle fibres are specialized contractile fibres which respond to neural stimulation from the
higher centre (Brain or spinal cord) causing in an influx of ion into its sarcoplasm and
ultimately results in the depolarization of its local electrical field (Purves, 2008); this depolarized
electrical field then propagates through fluid-composed tissue and is measured at the level of
the skin (Reaz, Hussain & Mohd-Yasin, 2006). The recording method implemented in the lab is that of
a non-invasive method i.e. mounted to the skin of the subject, as a result the signal produced
in figure 1. Illustrates a composite of all the local action potentials produced by the muscular
tissue under the region which the electrodes were placed. During voluntary contraction,
electrical signal is transmitted from conduit of neuronal pathway from the Primary motor
cortex via alpha motor neurons to the muscle fibre targets (Purves, 2008). Evident from figure 1,
an increase in the voluntary contraction generated a larger amplitude as well as higher
frequency in the EMG signals. This observation can be explained with the fact that more
motor units are recruited in the process and therefore resulting in a greater degree of
depolarization of the local muscle fibres required for the action (Reaz, Hussain & Mohd-Yasin, 2006).
Because the recording method records the composite action potential of the motor units,depolarization of individual muscle fibres occur at random intervals and thereby resulting in
an increased frequency i.e. more electrical activity is packed within a given time frame. (Reaz,
Hussain & Mohd-Yasin, 2006) Despite a fairly obvious trend of increased amplitude and frequency
with increasing voluntary contraction, there is still evident (but minimal) electrical activity
even during the muscles resting stage; this may be due to multiple factors but appropriate
assumptions are the basal tone of Gamma motor neurons which helps to maintain a degree of
tautness and therefore calibrates the sensitivity of the muscle spindles (Purves, 2008). Another
potential cause is due to the electrical noise of the surrounding which may also be picked up
on the EMG recording. (Chowdhury et al., 2013)
The CMAP curves were of a biphasic nature, this is because the recording electrodes consistof both a positive and negative component; when CAP passes through the proximal electrode
it generates an upward deflection and vice versa (The Compound Action Potential (CAP) Of the Frog’s
Sciatic Nerve, 2005). Figures 2 and 4 illustrate the CMAP which is recorded upon differential
stimulation parameters (mA) at the ulnar nerve (elbow) and the median nerve (elbow)
respectively. The curves that are seen in these CMAP recordings show that of a graded
response i.e. increase stimulus parameter will result in a larger amplitude in signal. CMAP
signals differ from singular muscular action potential (“All or none-response) in the sense
that it records the action potential generated by a local composite of motor units. The signal is
graded because of the differential stimulus threshold of motor neurons; the larger neuronal
axons are more easily depolarized (excitable) than the smaller motor axons. When stimuli
parameter increases, more axons surpass this threshold potential and thereby recruiting alarger number of motor units (The Compound Action Potential (CAP) Of the Frog’s Sciatic Nerve , 2005). This
idea can be similarly superimposed to the regulation of muscular force i.e. when stimuli
parameter increased, the subject demonstrated a greater amount of force generated due to an
increased number of motor units recruited; this systematic relationship is regarded as the size
principle (Purves, 2008). In both figures 2 and 4, it is evident that below a certain stimulus
current, there is no definitive CMAP signal. In the CMAP recording for the ulnar nerve
(elbow), stimuli below 23 mA generated no signal, and in the recording for the median nerve
(elbow), stimuli below 45 mA generated no signal. The stimuli current to which a CMAP is
produced is known as the threshold potential. Threshold potential defines a point to which
stimulation will result in greater sodium influx (causing depolarization) compared to
potassium out-flux (repolarization) (Purves, 2008) and thereby causing propagation of action potential across the muscular tissue to produce the compound action potential. As well as a
MEDSCI 206 – Laboratory 2 “Human nerve conduction velocity” William Lin 6737564
threshold stimulus, supramaximal stimulus currents were also recorded for both the ulnar and
median nerve (elbow, ref. figure 2 and 4) at 75 mA and 90 mA respectively. Supramaximal
stimulation exists because there is a finite number of motor units recruited and further
stimulation past this point will have an uncorrelated relationship to motor units recruited.
(Campbell, n.d.)
Figures 3 and 5 illustrates the supramaximal stimulation of the ulnar and median nerve at
both the elbow and wrist joint respectively. In figure 3. The conduction velocity is calculated
to be 43.17 ms-1 and 61.162 ms-1 in figure 5. The conduction velocity at these both sites all
fell within the normal range of conduction velocities (51-75 ms-1 for ulnar nerve conduction
and 49-74 ms-1 for median nerve). However, when we compare these conduction velocities
values, it is evident in our subject that the conduction velocity for the median nerve (61.2 ms-
1) was much higher than that of the ulnar nerve (43.2 ms-1). This difference in conduction
velocity could be attributed to the fact that it has been proposed that the median nerve is
generally larger in diameter compared to that of the ulnar nerve (Kundu, Harreby & Jensen, n.d.); a
larger diameter of the axon will result in a decrease of internal resistance to current and
increase passive current flow (Purves, 2008). Furthermore, other factor which may attribute tothe increased conduction velocity of the median nerve is a notion regarding neuromuscular
perisynaptic Schwann cell activity in regulating myelination and plasticity of motor neurons
as a result of increased muscle memory etc (Auld & Robitaille, 2003). In figure 3, the amplitude of
CMAP signal between ulnar nerve at the elbow and wrist suggested that the CMAP signal at
the wrist was lower in amplitude to that in the elbow. This observation is most likely due to
the fact that electrodes are placed quite distal to the nerve such that only more terminal nerves
may be stimulated (Martini, Timmons & Tallitsch, 2012). However, in figure 5, an opposite
observation was made such that the wrist CMAP signal of the median nerve was larger than
that at the elbow. This could be due to human error i.e. subject may have been moving when
recordings were made and therefore adding electrical noise to the signal recording. When
looking at the class data, average values of 50.7 ms-1 (Ulnar nerve) and 49.7 ms-1 (Mediannerve) were calculated (ref. table 1); although these values all fall within the normal ranges of
nerve conduction velocity (ref. Part B), they all situate at the lower limits of their
physiological normal range. A Factor which has a positive relationship to nerve conduction
velocity is temperature; an increase in temperature affects to reduce the temperature
dependent velocity and thus increases conduction velocity (Waxman, 1980). Factors which have a
general negative correlation to conduction velocity are: Hand factors e.g. index finger
circumference, Height (decrease in 0.5 m/s per inch increase in height) and sex, which is not
valid in this experiment because subjects are all of similar age (18-20). (Stetson, Albers, Silverstein
& Wolfe, 1992)
Variables applicable to the Nerve conduction experiment can be narrowed to some of thefollowing: There may be variation in experiment protocol between different groups e.g. Some
groups may have had another member (other than the subject themselves) holding the
stimulating electrode; this is more likely to reduce a degree of error when recording as the
subject may move when muscles contract therefore resulting in additional electrical noise.
There is also an undeniable factor of individual variation; as mentioned in the above
paragraph, different personal factors and anthropometric factors will ultimately affect the
results of the nerve conduction velocity. Time limit on certain groups would have meant that
some groups did not have time to repeat measurements and therefore leaving a possibility that
results may have been inaccurate but no further time was allowed to make repeated
measurements. Some errors which may have resulted from these variables are the differential
placement of electrode between each recording, which will ultimately affect the region of
stimulation to a certain extent. Furthermore, some subjects may feel anxious or nervous
MEDSCI 206 – Laboratory 2 “Human nerve conduction velocity” William Lin 6737564
References
Auld, D., & Robitaille, R. (2003). Perisynaptic Schwann Cells at the Neuromuscular Junction:
Nerve- and Activity-Dependent Contributions to Synaptic Efficacy, Plasticity, and
Reinnervation. The Neuroscientist, 9(2), 144-157. doi:10.1177/1073858403252229
Boron, W., & Boulpaep, E. (2012). Medical Physiology, 2e Updated Edition. London:
Elsevier Health Sciences.
Campbell, W. Essentials of electrodiagnostic medicine.
Chowdhury, R., Reaz, M., Ali, M., Bakar, A., Chellappan, K., & Chang, T. (2013). SurfaceElectromyography Signal Processing and Classification Techniques. Sensors, 13(9), 12431-
12466. doi:10.3390/s130912431
Han, B., Lin, O., & Isherwood, G. (2015). Human nerve conduction velocity (p. Results:
Figure).
Hopkinsmedicine.org,. (2015). Nerve Conduction Studies | Johns Hopkins Medicine Health