I lean against this a bit. The added specificity of ‘cytosol’ is not incorrect, but I think it’s an unhelpful detail considering the context of intracellular transfer of calcium in this case.
If it were talking about muscle contraction, or something, where the ER is a relevant context, I could see it, but given the specifics of cell-surface ligand-gated channels and a generalized explanatory model of neurotransmitter communication I think “outside the cell” is ultimately more fitting here. Open to thoughts, tho