Teacher professional growth : a study of primary teachers involved in mathematics professional development

Abstract

The membrane of a living cell consists of a bilayer of amphipolar lipid molecules as well as much larger proteins. Transmembrane potentials of up to 120 mV are physiologic and well tolerated, but when the potential is more than 300 mV, this lipid bilayer is unstable. Pores are then formed through which measurable flow of ions can occur. We follow currents through frog muscle cell membranes under 4-ms pulses of up to 440 mV. We present a theory that allows us to describe the relaxation of the current back to zero after the pulse in terms of membrane parameters. We obtain a line tension of 3.6 x 10(-6) N, which is similar to that found in artificial lipid bilayers.