Musculoskeletal robots hold significant potential for the design of future robots. One of the challenges is the possibility of output delays from the muscles, which may prevent higher centers from compensating during sudden disturbances. The reflex system, widely observed in animals, is viewed as an efficient mechanism for overcoming this challenge. Specifically, the Ia and Ib reflex pathways, as the sensory pathways originating from muscle sensory receptors, are considered to contribute to the responsiveness and convergence of the feedback system with the dynamics of the musculoskeletal body. In this study, we propose a basic reflex system that can be implemented into a robot arm driven by pneumatic artificial muscles (PAMs) and investigate its effectiveness through two experiments: a sudden force shock and a position constraint. The results demonstrate that the reflex behavior is capable of reducing the impact of disturbances, with the Ia reflex pathways providing an immediate response to disturbances and the Ib reflex pathways curbing excessive output force.