For example , a neurotransmitter , hormone , or atomic ions may each bind to the extracellular domain as a ligand coupled to receptor .
By definition , a receptor 's main function is to recognize and respond to a type of ligand .
A neurotransmitter , hormone , or atomic ions may each bind to the extracellular domain as a ligand coupled to receptor .
By definition , a receptor 's main function is to recognize and respond to a type of ligand .