Diffusion of Ions Through Cell Membrane
Due to their large size (all ions
in solution are hydrated) as well as their
charge, ions cannot diffuse through the cell
Ions enter the cell membrane
through ion channels composed of proteins that
span the cell membrane.
These channels are usually highly
selective i.e. they will let through only one
type of ion or a small number of ions.
This selectively is due the
- diameter of channel
- internal charge
- length of channel
- shape of internal channel
- Certain channels are gated.
- By gated, one means that the
channels are either open or closed.
- These gates are either controlled
through chemical signals (ligand gated)
or by electrical changes (voltage gated)
- Though utilising protien channels,
the ions would still be diffusing down their
concnetration gradient and hence there is no