Stimulating Electrode

1. What is the difference between the cathode and the anode of the stimulating electrode?
2. What is an anodal block?
3. What is the difference between maximal, submaximal, and supramaximal stimulus?
4. What are the artifacts that occur with too high a stimulus?
5. How long should the stimulus duration be?

Answers:
1. The cathode generates a negative impulse and attracts positive charge. The anode generates a positive impulse and attracts negative charge.
2. An anodal block is a theoretical local block that occurs when the stimulator's cathode and anode are reversed. The nerve is hyperpolarized and an AP is inhibited.
3. The maximal stimulus is the intensity at which no further increase in evoked potential will occur with added stimulus intensity. Submaximal stimulus is below the maximal stimulus but above the threshold stimulus. Supramaximal stimulus is 20% above maximal.
4. Latency may appear decreased due to increasing surface area stimulated, and surrounding nerves and muscles may be stimulated and alter the waveform.
5. 0.1 to 0.3 milliseconds.