Question

Consider a motor neuron: Diameter = 100 um Permittivity of vacuum = 8.85 x 10-12 Farad/m Dielectric constant of plasma membrane = 8 Faraday's constant = 96,500 coulombs/mol Cell osmolarity = 290 mOsM; estimate 50% are positive ions What percentage of the positive ions within a cell need to cross the membrane to create a -80 mV Em? Hints: Find how much charge is needed to generate Em using Q=C*V (as discussed in class). Convert the charge (coulombs) to moles of charge using Faraday's constant. This is the total number of ions that need to cross the membrane to generate the membrane voltage. Next calculate the number of positive ions in the cell based on the values given.

Answer 1

Charge, Q = CV The capacitance, c is given by C = ATTEKR (Sphere) = 4TX 8.85*10' X 8 X 100 X10 = 0.00502x8.85x102 - 14 r 4.44 x 10 F Q = CV = 4.44x10 " x 80 tx10x80x103 17 -355.2X10 = 3.552x1050 -20 Moles = Q - 3.552x10 = 3.68 X 10 moles Faraday's 96,500 constant Cell osmolarity = 290 most For 1x 103 moles, ions generated are 290 so for 3.68x1020 moles, ions are as. 3.68x10° °x290 .. =1067.44x 1.0 = 1.067x16/4 50% estimate are positive ions .. positive ions = 1.067x1014 - 5.335xio's moles