The animation below illustrates how the flow of positively charged ions
into the axon leads the axon to become positively charged relative to the
outside. With each positively charged sodium ion that enters the axon,
another positive charge is inside and one fewer negative charge is outside
the axon. Thus, together the inside grows increasingly more positive and
the relative concentration of sodium inside the axon relative to outside
the axon grows greater.
This initial phase of the action potential is called the depolarization
phase. Now as the depolarization phase progresses, the status of the
two physical forces that have been discussed changes. At the end of the
depolarization phase, the voltage of the inside of the axon relative to
the outside is positive and the relative concentration of sodium ions inside
the axon is greater than at the beginning of the action potential.
the end of the depolarization phase, what is the tendency for movement
of a sodium ion at the mouth of a sodium channel?