What are the differences between internal receptors and cell surface receptors?

Internal receptors and cell surface receptors are two broad categories of receptors that participate in most types of cell signaling pathways. There are several differences between the two. 

Internal Receptors

Internal receptors are receptor proteins that are present inside the cell in the cytoplasm or the nucleus. They are also known as intracellular receptors. These receptors respond to hydrophobic (water-hating) ligands that cross the plasma membrane and enter the cell. The ligands of internal receptors are typically small, hydrophobic molecules, which enables them to cross the plasma membrane to reach their receptors inside the cell. 

Cell Surface Receptors

Cell surface receptors are receptor proteins that are found embedded in the plasma membrane.  They respond to external ligands that do not need to travel across the plasma membrane. This allows several different types of molecules to act as ligands of cell surface receptors including large, hydrophilic or water-loving molecules.