In exocytosis, the membrane of the vesicle fuses with the membrane of the synaptic terminal. Without a compensatory mechanism, the pre-synaptic membrane would enlarge as vesicular membrane would continuously be added to the plasma membrane. This enlargement, however, does not occur as the vesicle membrane is retrieved from the pre-synaptic membrane and is recycled to form another synaptic vesicle. Following exocytosis, excess membrane on the synaptic terminal forms a pit coated with the protein clathrin. This clathrin-coated pit pinches off from the pre-synaptic membrane and, after the clathrin is removed, re-forms a synaptic vesicle.
Not all of the retrieved membrane is directly recycled into vesicles through the cistern. Some are returned to the cell body where it is degraded and processed into new vesicles which are then transported to the synaptic terminal.