In a demyelinating disease (e.g. multiple sclerosis), symptoms worsen with hot bath and improve with decreased temperature because:: (A) Lower temperatures slow the gating kinetics of Na+ channels, (B) AP duration increases with increased temperature, (C) Activity of K+ channels is increased at lower temperatures, (D) Inadequate recharging of the denuded axon at higher temperatures
Answer is A. In demyelinating diseases after myelin is degraded, there is redistribution of Na+ channels along the nerve (normally present at nodes of Ranvier). Lower temperature alters the Na+ channel kinetics in a way to delay the closure, thus extra Na+ can come into the cell, which enable electronic conduction upto the point on the nerve where the next Na+ channel is. At higher temperature: there is increased leakage of charges from the cell membrane k/o increased capacitance of the nerve.