[填空题]
During an action poteur2s .vt t)vuzx9;h h3ntial;3,;30 ertxe ;-fz 1icbg dwgvkot5vj, $Na^+$ ions move into the cell at a rate of about $3 \times10^{-7 }\;mol/m^2\cdot s$. How much power must be produced by the “active $Na^+$ pumping” system to produce this flow against a $+30-Mv$ potential difference? Assume that the axon is 10 cm long and $20\mu m$ in diameter. $ \times10^{-9 }\;W$
