Neural Control of Respiration in Fishes and Mammals

Publisher Summary This chapter discusses the neural control of respiration in fishes and mammals. In mammals, gas exchange is executed with sack-line lungs, ventilated tidally with the aid of diaphragmatic, intercostal, and abdominal muscles. The pump muscles are innervated from the spinal cord, where a part of their control mechanism is situated. Only some accessory respiratory muscles are innervated from, and consequently have their motor control circuits in, the brain. Muscle contraction in fishes is controlled under the influence of length- and tension receptors. In mammals, respiratory muscles contain tendon organs and active γ-innervated muscle spindles in varying quantities. In fishes, the respiratory water is propelled over the gills in a one-way direction by a pumping system powered by cranial muscles. These muscles are innervated by motor neurons in the brainstern, and their control mechanism is situated extremely close to the rest of the respiration regulation system and not at a distance in the spinal cord. The gills are equipped with a considerable number of small muscles, also innervated from the brain, that perform fine positioning movements and with mechano-receptors monitoring the progress of respiration. Both in mammals and in fish, the respiratory muscles do not have an exclusive respiratory function. The chapter explains how much of a basic ancestral control circuit had to evolve to adapt to differences in peripheral respiration systems in fishes and mammals.