Transcript Dr. Kennedy`s presentation

HKIN 473
Recording Motor Units
Recording Electrical Signals


Muscle fiber sarcolemma action potential is very small ~ 1
millivolt.
Therefore, to be able to record and “see” muscle activity
using indwelling electrodes, need to amplify the signal
first.



1) Preamplifier 2) Amplifier
For our laboratory, need to amp Motor unit signal by
between 1,000 and 5,000 times.
Gain = Output/Input (1 Volt = 1,000/1 mv)
Sampling Signals to Computer

Sample signals from Muscle Amp to computer using A/D
(analog to digital) converter.
Sampling Signals to Computer

Need to sample at the right frequency to see the detail of
the signal.

~10,000 Hz for MU recordings in humans

To do this, need to know:
1) the frequency (how many times a second) an event of
interest occurs (1, 10, 100 times a second?).
2) the detail of the signal you are sampling. If you do
not sample (look at signal) frequently enough may miss
events or not get a clear enough picture of the real
signal. In MU recordings we use shape of the potential or
its morphology to identify it as a single recording.
Recording Motor Units

Important Issues When
Analyzing Motor Units:

Single Unit Recordings
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Pay Attention to One Unit
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Sampling Issues
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
Motor Unit Morphology
(Shape)
This is done using both
visual signals
(oscilloscope) as well as
audio signals (units may
have different sounds)
Sensory Systems
External and Internal Stimuli
Vision
Higher Centers
Vestibular
Motor Systems
Somatosensory
Spinal Cord
Motoneurons
Sensory Feedback
Muscles
Motor Output
Sensory Systems
External and Internal Stimuli
Vision
Higher Centers
Vestibular
Motor Systems
Somatosensory
Spinal Cord
Kennedy and Cresswell 2001
Inglis et al. 2002
Kennedy and Inglis 2001
Motoneurons
Sensory Feedback
Muscles
Motor Output
Sensory Systems
External and Internal Stimuli
Vision
Higher Centers
Vestibular
Motor Systems
Somatosensory
Spinal Cord
Kennedy et al. (Submitted)
Kennedy et al. (In Press)
Kennedy and Inglis 2002
Motoneurons
Sensory Feedback
Muscles
Motor Output
Kennedy and Inglis 2001
Galvanic Vestibular Stimulation (GVS)
Galvanic Vestibular Stimulation (GVS)
Galvanic Stimulation and Muscle Reflexes
Cathode-Forward
Cathode-Left
Anode-Forward
Anode-Right
2 mV
Test Reflex
Conditioned Reflex
10 ms
Neurogram 1.4 mV
Force 200 N
Threshold
4s
No Stimulus
Anode
Cathode
Muscle Length and Motor Units
Environment
Sensory Signals
Effectors
CNS
Senses
Motor Response
Microneurography Set-up

Subject comfort

Reference Electrode

Recording Electrode
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Muscle Activity (EMG)
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Force Probe
Microneurography Explored
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Needle manually placed in a
peripheral nerve
Needle can record from
nearby axons
Shape of action potentials
dependent upon position of
needle
Maintained Indentation
Fast Adapting Type I
Fast Adapting Type II
Slow Adapting Type I
Slow Adapting Type II
Skin Receptors in the Foot Sole
Location of the Receptive Fields
Receptors
SA Type I
SA Type II
FA Type I
FA Type II
104
15 (14%)
16 (15%)
59 (57%)
14 (14%)
Skin Receptors in the Foot Sole

Slow adapting code
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Base of support
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Joint position
Base of Support

FastSurface
adapting
code
Contact
Slip
Center of
Pressure
Slip

Movement of the center of pressure

Detection of slip