Final answer:
Once the stimulus alters the receptor on the cell's membrane, the next step is that ion channels open, allowing ions to enter or exit.
Step-by-step explanation:
Once the stimulus alters the receptor on the cell's membrane, the next step is that ion channels open, allowing ions to enter or exit. This process allows for the movement of ions across the cell membrane, which can then lead to changes in membrane potential and cellular signaling. Examples of ion channels include ligand-gated channels that open in response to the binding of a neurotransmitter, and mechanically gated channels that open in response to physical stimuli.