How do ions enter the cell?

Ions enter the cell either via facilitated diffusion or active transport. 

Facilitated diffusion 

Facilitated diffusion is the selective passive movement of molecules across the hydrophobic plasma membrane. Ions diffuse into the cell through protein channels present in the plasma membrane. 

Protein channels facilitate the diffusion of ions down the concentration gradient, in which ions move from a region of high concentration to a region of low concentration, hence the name ‘facilitated diffusion’. 

Active transport 

Active transport refers to the movement of ions into the cell against a concentration gradient. Ions need to use cellular energy in the form of ATP to move from a region of low concentration to a region of high concentration.