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KIN 316 - Biomechanics of Tissue > Module 4 - Electromyography > Flashcards

Module 4 - Electromyography Flashcards

1
Q

What are some applications for Electromyography?

A
  • Clinical (diagnostic and monitoring)
  • Research
  • Ergonomics
  • Sport Sciences
  • Control Signals for devices or games
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2
Q

What is a motor unit?

A
  • Motoneuron and the muscle fibers it innervates
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3
Q

What is an innervation ratio?

A
  • Number of muscle fibers innervated by a motoneuron
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4
Q

What is the Neuromuscular Junction?

A
  • Special Synapse Between motor axon and muscle fiber
  • Neurotransmitter: Golgi Tendon Organ
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5
Q

How does the number of motor units and innervation ratio vary between muscles?

A
  • Small innervation ratio for eye and hand muscles
  • Large for leg and trunk muscles
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6
Q

What are some examples of muscles and their motor units and innervation ratios?

A

Abductor Pollicis Brevis
- MU: 171
- IR: 90
Rectus Lateralis
- MU: 4150
- IR: 5
Medial Gastrocnemius
- MU: 580
- IR: 1934

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7
Q

How does the nerve communicate with a muscle?

A
  • Synapse
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8
Q

What is the excitation-contraction coupling?

A
  • Ach binding results in depolarization of motor end plate
  • muscle fiber sarcolemma & action potential propagates from NMJ outwardly in all directions
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9
Q

What is the path of Excitation-Contraction Coupling?

A
  • Generation of motoneurons action potential
  • Release of Ach for presynaptic nerve terminal
  • Binding of Ach to muscle fiber Ach receptor
  • Depolarization of sarcolemma
  • Conduction of action potential into the fiber by T-tubules
  • Signaling of the SR by T-tubules to release Ca++
  • Binding of Ca++ to troponin - allows actin-myosin interaction
  • Force Generation (actin-myosin interaction)
  • Pumping of Ca++ back in SR
  • Ca++ concentration diminishes, muscle relaxes
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10
Q

What are the three muscle fiber types?

A
  • FF type motoneurons innervate FG muscle fibers forming FF type motor units
  • FR motoneurons innervate FOG type muscle fibers forming FR type motor units
  • S motoneurons innervate SO type muscle fibers forming S type motor units
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11
Q

What is a twitch profile?

A
  • excitation is rapid (5ms)
  • Contraction and Relaxation Slow (100ms)
  • If second impulse is superimposed, summation occurs
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12
Q

What is temporal summation?

A
  • Second impulse superimposed before first one has fully relaxed
  • Functional effect depends on the number of pulses and proximity
  • Multiple pulses results in higher force than single one
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13
Q

What is an unfused contraction?

A
  • temporal summation below 20Hz
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14
Q

Is it possible to distinguish an unfused contraction?

A

Yes
- Possible to distinguish pulses within the force record
- Distinguish individual twitches

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15
Q

Why is the net force smooth in human twitch profiles?

A

Motor units produce partially fused tetanus
- fire asynchronously with each other

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16
Q

How does Electromyography work?

A

Records Local Electrical Activity Associated with Muscle Activity
- Signal emitted each time a muscle contracts
- Muscle fiber action potential recorded
- Requires Electrodes and amplifier

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17
Q

What are the two types of electrodes used in EMG recording?

A
  • Surface Electrodes
  • Indwelling Electrodes
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18
Q

Describe the amplifier part of an EMG?

A

Gain and Dynamic Range:
- EMG signal up to 5mv (surface) and 10mV(indwelling)
- Gain of 1000 typical, noise of amplifier <20uV
- frequency response: 10-1000Hz (surface), 20-2000Hz(indwelling)

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19
Q

Is the Human Body a good conductor?

A
  • YES
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20
Q

What can cause disruption or cross-talk with EMG?

A
  • Power cords
  • Fluorescent Lighting
  • Electric Machine
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21
Q

Describe the process of EMG surface Recording.

A
  • Surface electrodes are placed on the skin overlying the muscle of interest
  • Frequently used
  • Simple and non-invasive compared to indwelling
  • Electrical activity is recorded from portion of muscle
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22
Q

What is the spatial summation of muscle electrical activity?

A
  • depth of MU determines relative strength of signal and shape
  • Deeper MU take longer to travel to surface
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23
Q

What is the temporal summation of muscle electrical activity?

A
  • Conduction velocity influences shape of MU
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24
Q

What are the important technical considerations of EMG surface recordings?

A
  • Position of Electrodes
  • Inter-Electrode Distance
  • Electrode Area
25
Q

How does the Position of Electrodes impact the EMG surface Recording?

A
  • Must be placed on one side of the innervation zone
  • Best Practice: middle third of distance between innervation zone and muscle tendon interface
26
Q

How does the Inter-Electrode Distance impact EMG surface recording?

A
  • Smaller distances lead to higher frequency content
  • Generally, 20mm is acceptable
27
Q

How does the Electrode Area impact EMG surface recording?

A
  • Smaller surface area leads to larger EMG signal
  • Smaller duration of MUAP & less cross-talk
28
Q

What factors influence EMG Signal?

A
  • Quality of amplifier and recording equipment
  • Electrodes configuration: area and shape
  • Number of active motor units
  • Depth and location of active fibers
  • Amount tissue between surface of muscle and electrodes: spatial filtering
29
Q

What man-made noises can be introduced from sources other than muscle?

A
  • Mainly comes from power lines (60Hz in NA)
  • Motor and other electric instuments
30
Q

What biological noise can interfere EMG?

A
  • Electrocardiogram when recording thoracic muscles
31
Q

What are artifacts in relation to EMG?

A
  • False signals generated by electrodes or cables
32
Q

How can EMG artifacts be movement related?

A
  • Movement of the cables or touching the electrodes
33
Q

What are the limitations of EMG surface recording?

A
  • Crosstalk
  • Movement Artifacts
  • Deep Muscles
  • Individual MU
34
Q

What is Crosstalk?

A
  • Activity of nearby muscles contribute to EMG of the muscle under investigation
35
Q

What are movement artifacts related to EMG surface recordings?

A
  • Frequent during explosive movements or electrode contract
  • Can usually be extracted because limited to low frequencies
36
Q

How are deep muscles a limitation to EMG surface recordings?

A
  • Cannot record EMG from deep axial muscles
37
Q

How are individual MU’s a limitation to EMG surface recordings?

A
  • Cannot identify single MU activity with a single differential surface EMG recording
38
Q

Explain 2D array of Electrodes.

A
  • Localization of EMG modulation
  • Identification of Muscle Fibers
  • MU firing patterns
39
Q

In what orientation do you place high-density surface EMG?

A
  • Position of the innervation zone
  • Muscle fiber conduction velocity
40
Q

Describe the EMG indwelling recording practice.

A
  • Different shapes and often homemade: wires or needles
  • Invasive
  • Allows for recording specific muscle: crosstalk eliminated
  • Remains the gold standard for single MU recordings
  • Can record from deep muscles
  • Possible determine recruitment order/rate coding/influence of MU in functional tasks
41
Q

What is rate coding?

A
  • Physiological strategy to alter force by altering activation frequency (temporal summation)
42
Q

What are limitations of EMG indwelling recordings?

A
  • Records only from a small portion of a muscle
  • Technically difficult and invasive (compared to Surface)
  • MU shape is time consuming to identify
43
Q

Is muscle activity synchonized?

A

No
- Temporal and spatial summation of all MU’s active near the electrode during a task

44
Q

What is an exception to non-synchronized muscle activity?

A
  • Muscle Fatigue
  • Electrical Stimulation (link to ECG)
45
Q

Why do you need other sensors to understand muscle action?

A
  • Can record identical EMG signals from different type of contrations
46
Q

Does EMG measure muscle force?

A

No
- can try to establish muscle force relationship

47
Q

What is an application for force relationship from EMG?

A
  • Robotic Control of balance or assistive devices
48
Q

Explain EMG’s oscillatory electrical activity.

A
  • Positive and Negative components
  • If we average raw single, value near zero
49
Q

How do we rectify EMG signals?

A
  • Envelope of rectified signals
  • Integrated EMG, RMS, Power
50
Q

What is the simplest comparison of EMG-Force Relationship?

A
  • Isometric contraction
  • One value of force can be compared to one value of EMG
  • Avoid problems associated with muscle length and velocity & muscle movement under the electrodes
51
Q

When is the EMG-Force relationship good?

A
  • When electrode position is stable with respect to active muscle fibers
  • When Motor Unit Activation pattern is stable
52
Q

When is EMG-force relationship not predictive?

A
  • May only be a coarse predictor of muscle tension
  • Invalid if muscle length changes rapidly
53
Q

What are some anatomical factors in the EMG-force relationship?

A
  • Shape of neuromuscular systems
  • Thickness of subcutaneous fat
  • Size & distribution of motor unit territories
  • Innervation Ratio
  • Pennation Angle
54
Q

What is the measurement system for EMG?

A
  • Electrode Size
  • Shape
  • Placement
  • Impedance
55
Q

What are the geometrical properties of EMG recording?

A
  • Muscle fiber shortening
  • Movement of muscle relative to electrodes
56
Q

What are the physical factors of an EMG recording?

A
  • Conductivity of tissues
  • Cross-talk
57
Q

What are the physiological factors of an EMG recording?

A
  • Conduction Velocity
  • Number of MU activated
  • Distribution of Discharge Rates
  • Synchronization
58
Q

What is EMG?

A
  • Recording of Electrical Activity associated with muscle contraction
59
Q

What are the key points of EMG?

A
  • Does not record muscle force
  • Can be done with surface or indwelling electrode
  • Both techniques have advantages
  • Depending on the question both can provide relevant information

KIN 316 - Biomechanics of Tissue (11 decks)

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