Final answer:
The gaps between adjacent Schwann cells on an axon are called nodes of Ranvier, which are essential for the rapid transmission of nerve impulses.
Step-by-step explanation:
The gaps between adjacent Schwann cells on an axon are called nodes of Ranvier. These gaps are crucial for the rapid transmission of nerve impulses along the axon through a process known as saltatory conduction, where nerve impulses 'jump' from one node to the next. The myelin sheath, produced by Schwann cells, insulates the axon and accelerates signal conduction, but at the nodes of Ranvier, there is no myelin, allowing for the regeneration of the electrical signal as it propagates down the axon.