Effects of the MRI during the MS. Left panel: distribution of angular velocity, Ω, when the core hydrogen abundance reaches X_c = 0.35 for different models. For model AN100, we show with a dotted line the mean molecular weight, μ. The area in grey indicates where the μ gradient is strong enough to suppress MRI activation in model AM100. Right panel: comparison at X_c = 0.35 of the unrestricted AM diffusion coefficient D = D_shear + D_MRI, given by Eqs. (23) and (10), for model AN000 (black) and model AM100 (red). The zone in shaded red shows the radial extension of the region where the MRI is active in model AM100.