Chemical substances that elicit action potentials in muscle group IV fibers in order of effectiveness are bradykinin, 5-hydroxytryptamine (serotonin), histamine, and potassium.

• 在酸痛的感觉是，主要由集团进行的第四传入纤维。第四组的肌肉传入纤维游离神经末梢是多型和应对各种刺激，包括化学，机械和热。