The slow depolarization to threshold that occurs between spikes is called the pacemaker potential. See that by changing the value of the current you can change the interval between the impulses. Discuss how this result illustrates, or is used by, sensory receptors to signal stimulus intensity. The long processes of most vertebrate neurons are myelinated. Myelin is the white matter of the central nervous system, and of peripheral nerves like the sciatic.
Impulses form only at the nodes - and propagate by jumping from one node to the next.
But if the nodes are too far apart, impulse conduction fails. Type 6 and until you see the jumping impulse. Develop and perform an experiment, and record your results, which measures the maximum spacing of the nodes for the impulse to just propagate.