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Wheels of Motion: Oscillatory Potentials in the Motor Cortex
Published in Alexa Riehle, Eilon Vaadia, Motor Cortex in Voluntary Movements, 2004
Mima and colleagues have shown that corticomuscular coherence is probably not due to reafferent signals from the contracting muscle.42 As subjects performed thumb and little finger apposition, vibration of the abductor pollicis brevis muscle tendon at 100 Hz had no significant effect on coherence (in either the mu or beta band). Similarly, functional deafferentation by ischemia failed to change corticomuscular coherence.6786 One may conclude that movement-related cortical oscillations reflect motor rather than sensory activity. Moreover, the location of peak beta corticomuscular coherence generally corresponds to the appropriate muscle representation in motor cortex, as determined by TMS.42
Electrodiagnostic Studies
Published in Joseph D. Bronzino, Donald R. Peterson, Biomedical Engineering Fundamentals, 2019
In the motor nerve conduction study (MNCS), surface electrodes are used to record the activity from a muscle innervated by the tested nerve. Figure 46.6a illustrates the setup for a median motor NCS. e “active” recording surface is over the belly of abductor pollicis brevis (APB) muscle, and a “reference” electrode is placed distally over the thumb. e rst stimulation site for the median nerve is at the wrist where the nerve is quite supercial. At minimal stimulus intensity, the electrical eld is insucient to depolarize any nerve bers. Hence, no response is registered. When the intensity is increased, some axons in the nerve will be stimulated (i.e., they will adequately depolarize to generate the AP). eir APs will propagate to the muscle and activate the muscle bers innervated by them. One may recognize a small twitch and a concomitant low-voltage electrical response on the display. When the intensity is increased, more nerve bers will be stimulated and the response will become larger (Figure 46.6b). One continues to increase the intensity until the amplitude (i.e., signal voltage) is maximized. is indicates that all nerve bers are stimulated. To ensure that the response is maximal, the intensity is increased further by 10-20% and the resulting potential is accepted for analysis. e signal is a sum of MUP of all MUs in the muscle and is called the “compound muscle action potential (CMAP)” (Figure 46.6c). In motor nerve conduction studies, the recording electrode is placed over the end-plate zone of the muscle. Since there is no approaching volley of APs, the CMAP does not have an initial positive phase. An initial negative (i.e., upward) deection is used as an indication of proper electrode placement.
Biological Monitoring: Neurophysiological and Behavioral Assessments
Published in Donald J. Ecobichon, Occupational Hazards of Pesticide Exposure, 2020
Using the median nerve (elbow-to-wrist portion), the conduction velocity is measured by stimulating the nerve supramaximally at the wrist (between the tendon of flexor carpi radialis and palmaris longus) and at the elbow medial to the tendon of biceps brachii and the bracheal artery (Misra et al. 1988). The recording electrode is placed on the belly of the abductor pollicis brevis, the reference electrode being placed over the tendon of the muscle and the ground electrode on the back of the hand (Misra et al.
Grip strength of occupational workers in relation to carpal tunnel syndrome and individual factors
Published in International Journal of Occupational Safety and Ergonomics, 2020
Greesh Kumar Singh, Sanjay Srivastava
Body areas were well cleaned with alcohol wipes before placement of surface electrodes to reduce resistance between contact surfaces due to skin oils, dust, etc. The skin was allowed to dry before applying electrodes. For motor nerve response, an active disc electrode (cathode) was placed on the belly of the abductor pollicis brevis (APB), and a reference electrode (anode) was placed on the tendon of the APB muscle, approximately 4 cm distal to the active electrode. A large grounding electrode was placed on the palm between the stimulating and recording electrodes. A standard measurement technique [24] was employed to record motor nerve conduction parameters (Table 2).