Neural Control of Cardiac Outflow through the Sternal Valve in the Lobster Homarus americanus

In the American lobster, the sternal artery and the dorsal abdominal artery arise from the bulbus arteriosus, which is located immediately behind the heart. A nonmuscular flap valve is located at the entrance to the bulbus, and a muscular bicuspid flap valve is located at the origin of the sternal artery. The sternal valve muscles receive inhibitory innervation. Stimulation of these nerves causes the muscles to relax and, in actively pumping hearts, to increase outflow to the sternal artery. The neurohormone proctolin causes contracture of these muscles, and outflow is reduced. Stimulation of the valve nerve overrides the effects of proctolin.