Final answer:
The trigeminal nerve (CNV) innervates the muscles responsible for mastication and is tested using stretch reflexes.
Step-by-step explanation:
The cranial nerve that innervates all muscles of mastication is the trigeminal nerve (CNV). This nerve is responsible for motor functions such as the control of muscles that enable chewing, which are tested using stretch reflexes. The trigeminal nerve has three branches that connect to muscles of the face, ensuring the coordination of actions such as mastication, and it is through this nerve that the masseter, the main muscle for chewing, receives its innervation.