EMG lab procedures - PSIO 201 Required Handout Department...

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PSIO 201 Required Handout Department of Physiology INTRODUCTION TO ELECTROMYOGRAPHY ____________________________________________________________________________________ Learning objectives: 1. Define electromyography (EMG) and describe the physiological basis of an EMG signal. 2. Describe how an EMG signal changes during an isometric contraction that proceeds from zero to maximal force production. 3. Be able to interpret the raw EMG recorded during an isometric contraction. This interpretation should include a basic understanding of the principles of motor unit recruitment and frequency, and how they contribute to the force produced by a muscle. 4. Describe how the EMG changes during a sustained isometric contraction, submaximal and/or maximal, that is held to fatigue. 5. Explain the two basic strategies that the nervous system employs to increase the force produced by a muscle: increased motor unit recruitment and stimulation frequency. ____________________________________________________________________________________ Introduction In this laboratory you will be introduced to the clinical and research technique called electromyography. Electromyography (EMG) is simply the measurement of the electrical activity of a muscle. The EMG provides an extracellular view of the changes in muscle cell membrane potentials that are linked with the propagation of action potentials. You will learn in the lecture portion of this course that an action potential is the electrical signal generated when an excitable cell (like a nerve or muscle cell) experiences a change in its resting membrane potential (or "charge"), caused by a movement of ions across the cell membrane. The electrical charge of a membrane is measured in millivolts ; at rest, the inside of a cell carries more negative charge than the surrounding environment, so its electrical charge is said to be negative. When a region of the cell membrane becomes excited, the interior of the cell becomes more positive because positively charged ions, namely sodium, enter the cell in large quantity. This local change in voltage (when the inside of the cell becomes positive) excites adjacent regions of the membrane until the entire length of the muscle cell membrane experiences a change in voltage. Special monitoring equipment can be used to measure the change in voltage across a cell membrane. In a typical EMG recording set up, two electrodes are placed over a particular muscle to detect the difference in electrical charge (millivolts) between the two electrodes. Electrodes essentially act as antennae, detecting the electrical activity of a cell or cells. Depending upon the size and location of the electrodes, this may represent the difference in electrical charge across one muscle fiber, the fibers in one motor unit, or all of the muscle fibers in an entire muscle. Note that small, intramuscular needle electrodes are required to measure the electrical activity of a single motor unit. To observe the electrical
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This note was uploaded on 09/11/2011 for the course PSIO 201 taught by Professor Stanescu during the Summer '08 term at University of Arizona- Tucson.

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EMG lab procedures - PSIO 201 Required Handout Department...

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