The ____________ ion channels are considered receptors because they only open when one or more ligands are bound. The ____________ ion channels are not considered receptors because they do not requir

a) Ligand-gated; Voltage-gated
b) Voltage-gated; Ligand-gated
c) Mechanosensitive; Ligand-gated
d) Chemically-gated; Mechanosensitive