Ion  channel receptors respond
   to  ligands  such  as neurotransmitters to open sodium gates and relay
   nerve impulses.
<P>
<Li> The gate is closed.
<Li> A  ligand binds to the receptor and the gate opens, Na^+ ions flow
through the channel.
<Li> The ligand dissociates from the cell, closing the gate.
<P>
   Note the difference with facilitated diffusion.