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 Pay Attention to One Unit Sampling Issues Motor Unit Morphology (Shape) This is done using both visual signals (oscilloscope) as well as audio signals (units may have different sounds)

External and Internal Stimuli Higher Centers Motor Systems Spinal Cord Motoneurons Muscles Motor Output Sensory Feedback Sensory Systems Vision Vestibular Somatosensory

External and Internal Stimuli Higher Centers Motor Systems Spinal Cord Motoneurons Muscles Motor Output Sensory Feedback Sensory Systems Vision Vestibular Somatosensory Kennedy and Cresswell 2001 Inglis et al Kennedy and Inglis 2001

External and Internal Stimuli Higher Centers Motor Systems Spinal Cord Motoneurons Muscles Motor Output Sensory Feedback Sensory Systems Vision Vestibular Somatosensory Kennedy et al. (Submitted) Kennedy et al. (In Press) Kennedy and Inglis 2002 Kennedy and Inglis 2001

Galvanic Vestibular Stimulation (GVS)

Galvanic Stimulation and Muscle Reflexes Cathode-ForwardCathode-Left Anode-ForwardAnode-Right 10 ms 2 mV Test ReflexConditioned Reflex

Threshold 4 s Neurogram 1.4 mV Force 200 N No Stimulus AnodeCathode

Muscle Length and Motor Units

Senses Effectors CNS EnvironmentMotor ResponseSensory Signals

Microneurography Set-up Subject comfort Reference Electrode Recording Electrode Muscle Activity (EMG) Force Probe

Microneurography Explored 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 104 SA Type I 15 (14%) SA Type II 16 (15%) FA Type I 59 (57%) FA Type II 14 (14%)

Skin Receptors in the Foot Sole Slow adapting code Base of support Joint position Base of Support Surface Contact Slip Center of Pressure Slip Fast adapting code Movement of the center of pressure Detection of slip