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Lab Techniques (321) > Neuromuscular > Flashcards

Neuromuscular Flashcards

1
Q

draw the motor neuron and label its components

A
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2
Q

what is a ‘pool’ of MN’s?

A

an amount of MN;s in the spinal cord that control a given muscle or muscle group

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3
Q

what do motor neurons do ?

A

they receive and integrate excitatory and inhibitory inputs from neurons originating in the brain, spinal cord and periphery

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4
Q

what is the definition of a motor unit (MU)

A

a motor neuron and the muscle fibres it innervates

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5
Q

tension is inversely proportional to MU size - true or false

A

false- directly proportional

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6
Q

low innervation ratio ( small #) will do what

A

rely more on rate coding than recruitment to increase force output

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7
Q

what is the size of an action potential recorded by intramuscular EMG indicative of

A

( microphone analogy ) how close the active motor unit is to the recording site

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8
Q

higher innervation ratio ( large #) will do what

A

more coarse control ( e.g. trunk and proximal limb muscles )

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9
Q

type 1 (s) motor unit properties:

A

smallest
high oxidative
low glycolytic
slow twitch
low fatiguability

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10
Q

type IIa (FR) motor unit properties:

A

medium size - recruited second
medium oxidative
high glycolytic
fast twitch
low fatiguability

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11
Q

type IIb (FF) motor unit properties :

A

largest
low oxidative
high glycolytic
fast twitch
high fatiguability

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12
Q

what is the hennemans size principle?

A

excitatory input required to reach threshold increases with soma size (i.e. activation threshold increases with soma size)
- recruited smallest to largest because less energy required to recruit smaller first

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13
Q

functional consequences of hennemans size principle

A

-simplifies the task of modulating force

  • ensures a smooth increase in force production
  • minimizes fatigue as slow twitch, fatigue - resistant muscle fibres are activated first
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14
Q

how is force production controlled

A

-motor neuron pool controls force by :

-number of active motor units (recruitment)
-discharge rate of active motor units ( rate coding)

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15
Q

do all muscles use rate coding and rectuitment to the same extent? why or why not

A

no, control strategy varies by muscle due to:
-number of motor units
-force (% maximum) at which recruitment is complete
-maximal discharge rates

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16
Q

what is surface EMG

A

-non invasive way of measuring motor neuron output (listening to a convo through a door)

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17
Q

set-ups for voluntary surface EMG

A

-MONOPOLAR SET-UP (electrodes far apart)
- highly sensitive to ‘cross-talk’ (will pick up signals from other muscles)
-best for evoked responses

-BI-POLAR SET-UP (electrodes closer)
-most common set-up
-less sensitive to cross-talk
-willl have more phase cancellation and amplification (weird evoked responses like an M wave)

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18
Q

if you measure EMG across days.. what would you need to control?

A

-placement of electrodes
-environmental factors (humidity)

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19
Q

raw emg provides relatively little information - true or false

A

true

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20
Q

what are the common processing methods of surface EMG

A
  • root mean square (RMS) amplitude
    -full-wave rectification (rectified EMG)
    -integration (integrated EMG ; iEMG)
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21
Q

what is the root mean square method (RMS)

A

calc works in reverse- S-M-R
1) square all amplitudes (to prevent + and - values from cancelling)
2) calculate mean of all amplitudes from part 1
3) take the square root of the mean from pt2

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22
Q

what is the full-wave rectification method

A

where absolute values are taken of each data point so the entire waveform is positive

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23
Q

what is the integrated EMG method (iEMG)

A

calculated as the area under the curve of rectified EMG signal (units change from mV to mV.s to reflect the inclusion of time)

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24
Q

what is the equation for force/what is force

A

F= ma
-a push or pull
-pulling forces are tensile forces

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25
Q

what is muscular force

A

measure of the tension developed by a muscle

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26
Q

what is torque/ equation for torque

A

turning effect caused by a force about an axis
T= Fr (r=momentum arm)

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27
Q

what is muscular torque

A

torque produced by muscles is responsible for movement of our limbs about our joints

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28
Q

where do slow-twitch fibres tend to be located

A

tend to be more centrally located

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29
Q

what is innervation ratio equal to

A

innervation ratio = # of muscle fibres/ MU

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30
Q

what is phase cancellation when looking at a surface emg ?

A

if the muscle fibers are misaligned or oriented in a way that produces signals with opposite phases, the EMG signals may cancel each other out, leading to a reduction or elimination of the recorded signal. This phenomenon is known as phase cancellation.

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31
Q

what are the limitations of surface emg

A

-gives limited insights into characteristics of the active MUs

-volume conduction (the action potentials are recorded a long way from their source)

  • low pass filtering (adipose tissue and skin drastically alter the signal)
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32
Q

what is INTRAMUSCULAR EMG (IEMG)

A

(like inserting a microphone into a choir and trying to figure out which one is singing)

  • electrode inserted into a muscle can record motor unit potentials (MUPs) at close range

-yields data about - discharge rates, recruitment and derecruitment and signal complexity

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33
Q

limitations of iEMG

A
  • Reflects activity of a small number of MUs near the recording zone of the electrode
    -challenging to track the same MUs
    -invasive
    -best suited to low-moderate intensity iso contractions
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34
Q

what are the different types of electrodes

A

-tungsten microelectrode
(0.125mm diameter)

-Fine wire
(0.05mm diameter/ inserted via a 25 gauge hypodermic needle

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35
Q

amplitude of MUP is NOT indicative of MU size (tension or innervation ratio) - true or false

A

-true
indicative of proximity to recording zone

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36
Q

what is the onion skin model

A

discharge rates decrease from earliest to latest recruited MUs (high motor unit firing rates with low threshold units)

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37
Q

what is the reverse onion skin model

A

discharge rates increase from earliest to latest recruited MUs. (matches contractile speed of muscle fibres to discharge rates)

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38
Q

when would the reverse onion skin model be superior for?

A

-high force contractions / brief tasks

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39
Q

true or false: derecruitment thresholds are often higher

A

false , lower

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40
Q

true or false: discharge rates are lower are derecruitment

A

true

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41
Q

what is the clinical applications for transcutaneous electrical stimulation (TES)

A

-diagnostics, disease progression, and treatment methods
-used in physio clinics to help reactivate muscle fibres (e.g. post surgery)

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42
Q

what does stimulation of the nervous system within a research setting enable us to do?

A

-assess responsiveness of multiple sites within the central and peripheral nervous systems & muscle fibres
-seperate the nervous and muscular systems (electrical and mechanical responses)
-can be compared to voluntary responses to quantify central fatigue

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43
Q

what are the common sites of stimulation? (TES)

A

-cortical
-spinal
-peripheral nerve
-muscle belly

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44
Q

draw the motor pathway (pg 8 of NM 3)

A
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45
Q

What does spinal stimulation produce?

A

produces a short-latency response termed the cervicomedullary motor evoked potential (CMEP)

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46
Q

What does peripheral stimulation produce?

A

stimulation applied to a peripheral nerve will evoke a compound muscle action potential (CMAP a.k.a M-wave)

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47
Q

what is a maximal M-wave

A

increase stimulus intensity with successive stimuli until wave size reaches a plateau (Mmax)
-when size doesn’t increase despite an increase in current, all motor units of a muscle have been activated

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48
Q

what is the vital importance of Mmax?

A

-expressing responses to cortical or spinal stem as a % Mmax enables us to assess a comparable portion of the motor pathway
-across individuals
-with different stimuli within an individual

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49
Q

what is a twitch

A

response to a single stimulus

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50
Q

what is a doublet

A

response to 2 stimuli 10ms apart (i.e., 2 pulses @ 100hz)

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51
Q

what is tetanus

A

-response to multiple stimuli at low, moderate, or high frequencies (e.g. 0.5s or 1s @ 10, 20, 50 or 100Hz)

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52
Q

what is a train

A

-multiple stimuli that will evoke tetanus

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53
Q

what is Hz?

A

unit of frequency (impulses per second

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54
Q

what do force/torque responses assess?

A

allow assessment of intrinsic contractile properties of muscle
-influence of central ns has been removed

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55
Q

How are twitches and tetani measured? (In terms of)

A

-peak force responses
-rate of force development/relaxation
-time to peak and half-relaxation

Can be used to estimate central fatigue using the interpolated twitch technique (ITT)

56
Q

ADVANTAGES of peripheral nerve (i.e nerve trunk) stim

A

-depolarizers axons according to diameter, like how the muscle would naturally be activated (i.e., activated motor unites are randomly distributed through the muscle)

-easy to activate all axons

  • evoke high forces with a relatively low stimulus intensity (i.e. requires less current than muscle belly)
57
Q

DISADVANTAGES of peripheral nerve stim

A

-activates axons of other muscles innervated by that nerve (sometimes antagonists)
-can be difficult to maintain electrode position
-poor reducibility
-may not be accessible

58
Q

ADVANTAGES of muscle belly stim

A

-easy to maintain electrode position
-high reproducibility
-hence, it is commercially available

59
Q

DISADVANTAGES of muscle belly stim

A

-activates muscle fibres closest to skin
-fast-twitch fibres tend to be superficial so fatigue occurs rapidly
-can’t activate all nerve endings (muscle fibres)
-antagonist muscle will be stimulated if intensity is too high
-relative to nerve trunk stimulation, requires a higher stimulus intensity to evoke a given force (increased discomfort)

60
Q

Cortical stim evokes which response

A

MEP (motor evoked potential)

61
Q

Spinal stim evokes which response

A

CMEP/H-reflex (cervicomedullary motor evoked potential/ Hoffmann reflex)

62
Q

Peripheral stim evokes which response

A

M-wave/Mmax

63
Q

What physiological mechanisms contribute to sex-based differences

A

-muscle perfusion
-skeletal muscle metabolism
-fibre type properties

64
Q

What non-physiological mechanisms that contribute to sex-based differences

A

Bias in sex-based research where males are researched more than females in both Human and animal models

65
Q

What are the general sex-based differences

A

-anatomical and physiological differences between the sexes that often lead to functional differences in performance and fatiguability

-magnitude of sex differences (if they exist) are TASK DEPENDENT (duration, intensity, speed of contraction, muscle group involved, environmental factors .. etc)

66
Q

General male differences

A

Typically have greater muscle mass and their whole muscles are often stronger and can produce more power compared to females
-faster contractile properties
-Greater reliance on anaerobic /glycolitic metabolism

67
Q

General female sex-based differences

A

Generally have greater proportional area of type 1 muscle fibres, less fatiguable
-greater reliance on oxidative properties
-slower contractile properties

68
Q

When intensity is lower and contractions /exercise is sustained, females often fatigue _______ than males

A

Less

69
Q

How do we compare relative changes

A

Normalize

70
Q

Explain the steps of EC coupling and explain what could happen if there is a problem with one of the steps

A
71
Q

What are internal forces

A

-forces that act within the object or system (body)

72
Q

What are external forces

A

-forces acting on an object or a system (non-contact force=gravity)

73
Q

What are some internal factors which influence the maximal force developed by a muscle

A

-arrangement of fibres (muscle design)
-size (cross sectional area) of muscle fibres
-# of muscle fibres
-proportion of muscle fibre types
-intrinsic force of muscle fibers (strength per cross sectional area/specific strength)

74
Q

Draw a parallel muscle

A
75
Q

Draw a unipennate muscle

A
76
Q

Draw a bipennate muscle

A
77
Q

Draw a circular muscle

A
78
Q

Length in muscle design

A

In series arrangement of fibres
-maximizes the range of motion and shortening velocity but does not affect strength

79
Q

Width in muscle design

A

In parallel arrangement of fibers
-maximizes the force of the muscle (increases cross-sectional area)

80
Q

Angular muscle design

A

Fibers at an angle to the line of pull maximize the number of fibers for a given volume of muscle

81
Q

Whole muscle force is greater when fibers are on an angle because

A

There are more fibers

82
Q

What are some external factors that influence the maximal force developed by muscles

A

-length
-velocity
-neural drive to the agonist/antagonist muscles (e.g., voluntary drive)

83
Q

Maximal shortening velocity of a muscle fibre depends on :

A

-length (#of sarcomeres in series)
-fibre type (myosin ATPase control rate of cross bridge cycling)

84
Q

Shortening contractions (less F more V)

A

-faster actin and myosin slide past each other, the more binding sites are missed

85
Q

Lengthening contractions (F^ with V^)

A

-stretching of partially activated sarcomeres
-greater average force per cross bridge cycle
-faster cross bridge reattachment

86
Q

Isokinetic contractions

A

Angular velocity is constant and maximal torque exerted is measured

87
Q

Isotonic contractions

A

External load is “constant” and maximal velocity achieved is measured

88
Q

What is muscle power?

A

The ability to generate maximal force as fast as possible

P=F x v

-more relevant than muscle strength (force)
-most activities are dynamic (not static)
-impacted by both force and velocity

89
Q

Both III/IV afferents ‘sample’ the interstitial space within the muscle true or false

A

True

90
Q

III/IV afferents send information back to the PNS true or false

A

False -CNS

91
Q

How could we manipulate III/IV afferent feedback (I.e., attenuate and augment sensitivity) within a lab setting (I.e., increase feedback ?)

A

PECO (post exercise cuff occlusion)- because it traps metabolites which continues to stimulate the metaboreflex, without central command (voluntary drive)

92
Q

How do we decrease III/IV afferent feedback

A

Fentanyl block will partially block III/IV afferent feedback from the lower limbs when injected at L3-L4
^peripheral fatigue - decreases central fatigue =feel no pain

93
Q

What is cortical stimulation

A

Cortical stimulation can be done using -transcranial electric stimulation (TES)
-transcranial magnetic stimulation (tms) of the motor cortex is a commonly applied technique to investigate motor output

94
Q

What is TMS?

A

Transcranial magnetic stim
- TMS utilizes electromagnetic induction to depolarize the axons of neurons within the primary motor cortex

95
Q

What are the uses of TMS

A
  • Diagnostic tool
    Will indicate damage to motor pathway due to: - spiral cord injury (sci) - MS or amyotrophic lateral sclerosis - stroke
  • therapeutic technique
    Repetitive TMS (rTMS) has been shown to alter resting membrane potentials (and excitability ) of targeted cites within the CNS - used to treat movement & psychiatric disorders
  • research (single / double pulse)
    Age, sex - related differences, fatigue, environmental stress, etc.
96
Q

What are the different coil types?

A
  • Double (figure 8) coil
  • single coil
  • double cone coil
97
Q

What is the double (figure 8 ) coil used for

A
  • Most commonly used (most research is hand muscles)
  • most focused (placement is critical)
  • least powerful (useless for lower limbs)
98
Q

What is the single coil used for

A
  • 2nd most commonly used
  • low locality
  • moderately powerful (good for proximal arm muscles)
99
Q

What is the double cone coil used for

A
  • Least commonly used
  • low locality (placement is forgiving)
  • most powerful (needed for trunk and leg muscles)
100
Q

What does a motor evoked potential represent (MEP)

A

Represents excitability of the motor pathway

101
Q

What does the silent period represent

A
  • Represents inhibitory reflexes (intracortical inhibition)
102
Q

What does stimulation of the nervous system allow us to assess

A
  • Assess the responsiveness of multiple sites within the central & peripheral nervous systems & the muscle fibers themselves
  • separate the nervous & muscular systems (electrical & mechanical responses)
103
Q

What we the advantages of TMS

A
  • Less painful than electrical stim
  • car stimulate deep cortical neurons noninvasively
  • some types provide therapeutic treatments
104
Q

What are the disadvantages of TMS

A
  • Very expensive
  • requires high trained individuals
  • coil type matters
  • not everyone can receive the stimulus
105
Q

Which technique is commonly used to augment III/IV efferent feedback INDEPENDENTLY of voluntary drive

A

PECO

106
Q

How will III/IV muscle afferent feedback influence the development of peripheral fatigue during exercise

A

-III/IV muscle afferents are responsible for the Afferent arm (i.e., the sensor) of the cardiovascular and ventilators reflex responses to exercise

  • muscle perfusion and O2 delivery directly alter thefatiguability of skeletal muscle
  • therefore, neural feedback from working muscles (I. E. Intact muscle afferent feedback) is VERY important for endurance exercise capacity
107
Q

How will III/IV muscle afferent feedback influence the development of central fatigue during exercise

A

-III/IV afferent feedback from working muscles facilitates central fatigue by exerting inhibitory influences on central motor drive during exercise

  • when these afferents are partially blocked, central motor drive (as measured by iEMG) is much higher early on during a time trial, contributing to greater fatigue
108
Q

What is the advantages of blocking III/IV afferents

A

-highly reproducible responses
-less confounding variables than a single limb blockade

109
Q

Disadvantages of blocking III/IV afferents

A

-can only partially block the afferents of the lower limb (can only partially blocked the afferents of the lower limb (without knowing by how much)
-requires highly skilled personnel
-very invasive

110
Q

What might cause a rightward shift in a force-frequency curve?

A

-a faster muscle
-force needs a greater input to elicit same response
-sarcoplasmic reticulum (SR) quickly sequesters Ca2+
(Muscle requires a higher input to generate the same amount of force)

111
Q

What might cause a leftward shift in a force-frequency curve

A
  • slower muscle
    -force will summate more quickly
    -SR taking longer to sequester Ca2+
    -mostly due to slowed relaxation time (movement of Ca2+ in and out of SR)
112
Q

Right and leftward shifts in the force frequency relationship depend on …

A

How long it takes for force to summate. This happens because the contractile properties are faster or slower ( less to do with recruitment and everything to do with how much intracellular calcium is available to aid in cross-bridge cycling)

113
Q

Which of the 2 EMG responses elicited by TMS represents intracortical inhibition and what are the units of the measurement

A

The silent period (milliseconds)

114
Q

Which of the two EMG responses elicited by TMS represents the excitability of the motor partway and what are the units of the measurement

A

Motor evoked potential (MEP) (milivolts)
-normalized to Mmax

115
Q

What is the relationship between MEP amplitude and TMS output in the biceps brachii

A

Sigmoidal relationship

116
Q

What is the relationship between SP duration and TMS output in the biceps brachii

A

Linear relationship

117
Q

Validity vs reliability

A

Validity: refers to the accuracy of a measurement
Reliability: refers to the reproducibility of the measurement/technique ( how many times can you get the same results from one person (intra-) or between individuals (inter-))

118
Q

What are the common wearables in the fitness tracking world

A

-movement sensors (pedometers, accelerometers, GPS)
-Physiological sensors (HR monitors, sleep monitors, temp sensors or integrated systems)

(Sensors can be highly variable (use different technologies) and detect multiple parameters)

119
Q

What is accelerometry

A

Small microelectromechanical devices that detect changes in acceleration (with reference to earths gravitational pull) as a mechanical disturbance which is then converted to an electrical signal.

This electrical signal is transmitted to an external device

120
Q

What are the 2 common methods that wearables use to measure HR?

A

-peripheral pulse detected by photoplethysmography (i.e., optical sensing technology)
(Assuming light can easily penetrate a well perfused area)

-electrical activity from the heart when recorded by electrodes embedded within a chest strap monitor

Both detect events over time to get a rebate (changes in saturation to RR intervals)

121
Q

Two common techniques wearables use to monitor temperature

A

-ingestible capsule that contains very small crystals that detect changes in the surrounding temperature (via vibration). This signal will be converted and transmitted to an external data log system

-wearable device (often an arm band) that will measure skin convective heat flux

122
Q

How do devices measure oxygen saturation (wearables)

A

-pulse oximetry uses spectrophotometry to determine how much hemoglobin is saturated with oxygen by emitting and detecting light through biological tissues

-oxygenated and deoxygenated hemoglobin have different light absorption rates ( oxygenated hemoglobin will absorb more light)

123
Q

How do sleep monitoring devices work?

A

will integrate multiple sensors that detect movement and physiological data
-accelerometry
-heart rate and or a strain gauge to detect chest wall movement
-O2 saturation
-nasal cannula to detect flow

Quality of sleep is often worse with the complexity of the devices

124
Q

What are some advantages of wearables

A

-most are useful (to an extent) for improving sport performance
-most brands are accurate when measuring steps and heart rate (although the latter is more variable)
-likely improve adherence to physical activity
-have been able to detect, record, and alert local emergency services when a potentially life threatening event has occurred

125
Q

Disadvantages of wearables

A

-expensive
-smartwatches often go for fashionable designs with less than optimal placements for accuracy (wrist is not well perfused)
-many claim to quantify sleep but will be using complex algorithms (with limited measurements) that over/under estimate sleep quality
-no brand accurately measures energy expenditure
-when measuring o2 saturation devices are highly susceptible to movement artifacts and not valid in all conditions ( extreme cold or peripheral perfusion is low/ poor validity at high altitude)
-inter-reliability (reproducibility between people) is often low because variation of skin colour & physical ability hasn’t been considered in product design

126
Q

Vestibular organs are ________ across the head

A

Mirrored

127
Q

What branch of the brain interprets the difference between firing rates as head motion

A

CNS

128
Q

What is the vestibulo-ocular reflex

A

Function :stabilize gaze (finger infront of face example)
Vestibular organs —-> ocular muscles

129
Q

What is the vestibulospinal reflex

A

Function: maintain upright balance
Vestibular organs—-> postural muscles

130
Q

What is electrical vestibular stimulation

A

-small electrical currents activate vestibular afferents

-mimics activity we would have if vestibular organs were actually sensing head motion

-CNS interprets this afferent activity —> we are falling

131
Q

What is the importance of the cathode/anode placement in electrical vestibular stimulation

A

CATHODE (-)
-Causes deploarization
-^ vestibular afferent firing rate (head will turn toward cathode)

ANODE (+)
-causes hyperpolarization
- decreases vestibular afferent firing rate

132
Q

How do vestibulospinal reflexes act on muscles during electrical vestibular stim

A

-act on muscles involved in the postural task to elicit compensatory balance responses
-balance response always directed to the anode
-biphasic—> short and medium latency responses
-medium latency (ML) response corresponds with overall activity of the muscle

-positive ML—> vestibulospinal reflex increasing EMG
-negative ML—> vestibulospinal reflex decreasing EMG

133
Q

Vestibulospinal reflexes are __________

A

Craniocentric

134
Q

Stimulation/sensation of head motion is bound between…

A

The inner ears

135
Q

Direction of balance responses dependant on head-on-feet posture —alters…

A

What muscle activation we see

136
Q

What are some considerations when using EVS

A

When using EVS to investigate vestibulospinal reflexes, the direction/size of the responses can be influenced by
-anode/cathode position
-positional and angle
-other sensory input

Lab Techniques (321) (4 decks)

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