This set of Biomedical Instrumentation Multiple Choice Questions & Answers (MCQs) focuses on “Electrodes for EMG”.
1. Which of the following is a preferred electrode for measuring EMG?
a) surface electrodes
b) needle electrodes
c) pregelled electrodes
d) scalp electrodes
Explanation: Electrodes for EMG work are usually of the needle type. Needle electrodes are used in clinical EMG, neurography and other electrophysiological measurements of the muscle tissues underneath the skin. Surface electrodes are preferred to measure ECG. Scalp electrodes for EEG.
2. Generally what is the material of needle electrodes?
a) stainless steel
Explanation: The material of the needle electrode is generally stainless steel. In spite of the face that stainless steel is unfavorable electrode material from the point of view of noise, it is preferred in EMG work. It is due to its mechanical solidity and low price.
3. Monopolar needle electrodes are having coatings of which material over the stainless steel wires which are bare only at the tips?
Explanation: The monopolar needle electrode consists of a teflon coated stainless steel wire. The wire is bare only at the tip. It is found that after the needle has been used a number of times, the teflon coating will recede, increasing the tip area. The needle should be discarded when this happens.
4. Which electrode can be used to pick up signals from individual fibers of muscle tissues?
a) biopolar needle electrode
b) concentric core needle electrode
c) multi-element needle electrode
d) monopolar needle electrode
Explanation: Multi-element needle electrodes are used to pick up the signals from individual fibers of muscle tissue. Special needles are available using 25-micron diameter electrode surfaces. They have up to 14 pickup surfaces down the side of one needle.
5. _______________ instrument is used to hold patients head and guide the placement of electrodes.
Explanation: For measurement of potential from specific part of the brain, longer needles are inserted inside the head. The needles are precisely located by means of a map or atlas of the brain. A special instrument called stereotaxic instrument is used to hold the subject’s head and guide the placement of the electrodes.
6. Number of cloud deployment models that are recognized are _________
Explanation: There are 3 recognized cloud deployment models. They are – Private cloud, Public cloud and Hybrid cloud.
7. The ground electrode is usually positioned over which body structures?
Explanation: The ground electrode is usually positioned over bony structures rather than over large muscle masses, in the vicinity of the recording and stimulating electrodes, and where possible, equidistant from them. Hairy areas don’t transmit proper signals. It increases impedance of the skin.
8. When intramuscular EMG is required to look into the electrical activities of deeper or overlaid muscles, ________ electrodes are used.
a) plate shape electrodes
b) surface electrodes
c) thin thread electrodes
d) fine wire electrodes
Explanation: When intramuscular EMG is required to look into the electrical activities of deeper or overlaid muscles, thin and flexible fine wire electrodes are used. These electrodes are inserted into the muscle site of interest. The needle or steel cannula is removed, and the electrode wires are connected to the steel spring adapters to minimize movement artefacts.
9. The contraction of the skeletal muscles results in the generation of action potential in the individual muscle fibers. Record of this action potential is called ______________
Explanation: The contraction of the skeletal muscles results in the generation of action potential in the individual muscle fibers, a record of such action potential is known as electromyogram (EMG). The activity is similar to that observed in the cardiac muscles (ECG or EKG), but in the skeletal muscles, repolarization takes place much more rapidly. The action potential lasts for only few milliseconds.
10. In voluntary contraction of the skeletal muscles, the muscle potential ranges from ________
a) 50 uV – 5 mV
b) 50 mV – 5 V
c) 0.05 uV – 2 mV
d) 50 mV – 500 mV
Explanation: In voluntary contraction of the skeletal muscles, the muscle potential ranges from 50 uV – 5 mV and duration from 2 to 15 ms. The values vary with the anatomic position of the muscle and the size and location of the electrode. In a relaxed muscle there are no action potentials.
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