For the myelinated nerve, the axon radius is 17 µm, the resistivity of the membr
ID: 1533441 • Letter: F
Question
For the myelinated nerve, the axon radius is 17 µm, the resistivity of the membrane is m = 1.0 107 m, the axoplasm resistivity is ra = 0.5 m. Assume that the myelin sheath thickness b is related to the axon radius a as a + b = 1.4a. (a) What is the electrotonus spread decay length (in cm) for this nerve? (Enter your answer to at least 2 decimal places.) (b) Using D = 243a to quantify the distance D between nodes of Ranvier for this nerve, how many nodes of Ranvier are triggered along the nerve as a result of a certain node being stimulated? Use a potential difference of V = 105 mV for the maximum potential change in the node that is initially stimulated, and allow other nodes of Ranvier to be triggered if electrotonus spread at their site causes at least a change from 70 mV to 57 mV. (Enter your answer as the number of whole nodes.)
Explanation / Answer
a) the electrotonus spread decay length = 17 * 10-6 * 107/(0.5 * 25 * 10000)
= 0.1360 cm
b) nodes of Ranvier are triggered = (105 * 80)/70
= 120