The electrical circuit model has the main block and the circuit. To model the structure of the circuit, create a Circuit Block and an associated Internal Block Diagram (IBD). The circuit has three parts: a source, a ground, and a resistor. These parts are of a different type since they all have a different behavior. It is necessary to create a Block for each of these parts. The picture below shows how the Internal Block Diagram look like. 

The Circuit IBD consists of three parts: source, ground and resistor.