Cours 2 CP NCI 2012 - Département de biologie

The unequal distribution of ions across the neuronal plasma
membrane is kept constant by active transport of ions
Concentration gradients for Na + , K + , Ca 2+ and Cl - ions are constant in the
external and cytosolic compartments.
Two hypotheses can explain this constancy:
1. Na + , K + , Ca 2+ and Cl - ions cannot cross the plasma membrane. In
that case, concentration gradients need to be established only
once in the lifetime.
2. Plasma membrane is permeable to Na + , K + , Ca 2+ and Cl - ions but
there are mechanisms that continuously re-establish the
gradients and maintain constant the unequal distribution of ions.