Instruments, systems and methods are provided for performing submucosal medical procedures in a desired area of the digestive tract using endoscopy. Instruments include a safe access needle injection instrument, a submucosal tunneling instrument, a submucosal dissection instrument, and a mucosal resection device. Systems include a combination of one or more of such instruments with or without injectable agents. Embodiments of various methods for performing the procedures are also provided. In accordance with one aspect there is provided a submucosal implant device for diagnosing and treating disorders of the body. The submucosal implant device may take the form of a gastric stimulator in which signals are supplied to the muscular wall of a mammal to treat motility disorders. In accordance with yet another aspect there is provided a method for performing a submucosal medical procedure to deploy a submucosal implant device in the digestive tract of a mammal.