Nerve Impulse Propagation The speed with which nerve impulses travel is determined in large part by the characteristic time constant T = RC of the circuit formed by the resistivity of the axon and the capacitance of its wall. The resistance of a 1.00-mm-long segment of an axon is 25.5 MΩ. (a) For nerve axons with no protective myelin sheath, the wall capacitance is about 3.14 × 10-10F for each segment of length L = 1.00 mm. Find the speed of the nerve impulses given by v = L/T. (b) Many axons are surrounded by a myelin sheath that decreases the wall capacitance to 1.57 × 10-12 F. What is the speed of nerve impulses along such myelinated axons?
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