Jellyfish nervous systems, among the earliest to evolve, and among the simplest in structure, integrate sensory signals from vibration, taste, gravity and photo-receptors with an on-going pacemaker activity that drives swimming. Integration of visual stimuli by Cubomedusae (box jellyfish) allows them to avoid obstacles while statocysts removal produces directionless swimming in many jellyfish forms. Other aspects of swimming modulated by sensory input include swim strength and swim frequency. The data reported are from a small hydrozoan jellyfish, Aglantha digitale, which escapes from predators by jet propulsion via contractions in its bell-shaped body wall (Donaldson, et al., 1980). Taste receptors affect swim frequency. When feeding, Aglantha stops swimming, perhaps because the high velocity water flow generated would otherwise detach captured prey from its mouth and tentacles (Mackie et al., 2003). The inhibitory signal which is initiated following manipulation of the prey by the mouth of the jellyfish is conducted to pacemaker cells distributed in a ring around the base of the animal (Mackie & Meech, 2008). Vibration sensors affect swim strength. Hair cell-like structures at the base of Aglantha (Arkett et al., 1988) sense vibrations produced by predators and trigger strong “escape” swims. The overall form of the contraction of the body wall associated with escape swimming differs from that during a normal “slow” swim. During escape swims the contraction is uniform while during slow swimming the contraction is confined to the upper half of the bell and is strongest near the eight radial giant motor axons that innervate the body wall. A combination of intracellular and “loose patch” (Roberts & Almers, 1992) recordings have revealed the different integrative processes that produce such varied swimming outcomes. Following a mechanical stimulus at the base of Aglantha a depolarizing post-synaptic potential (psp) activates voltage-gated sodium channels in the motor axon. The overshooting action potential elicited initiates widespread contraction in the sheet of electrically coupled muscle cells in the body wall. The low amplitude psp arising from the pacemaker system activates a low-threshold, low amplitude calcium spike based on activation of “T”-type calcium channels. Unlike the psp the calcium spike is propagated regeneratively and becomes large enough to activate low threshold channels in the muscle membrane. The associated contraction is weaker and more restricted. Conclusion: Complex behaviour in jellyfish arises from an easily accessible “Integration Surface” where propagating and “passive” electrical signals interact in a way that depends on the specific voltage-driven properties of specialized ion channels.