Central nervous system underlying fish swimming [A review]

Abstract

In the swimming of fish, thrust is generated by undulatory movements of the trunk muscles. The trunk muscles are composed of myomeres innervated by corresponding spinal segments, which are in turn composed of neural circuits which range longitudinally and interconnect. In each spinal segment there are various types of intemeurons and motor neurons, which together form a central pattern generator (CPG). Although each CPG can potentially generate its own swimming rhythm, the activity of each CPG is regulated by excitatory commands from the brain and by mutual excitatory and inhibitory interactions between intemeurons to produce controlled locomotion. The nucleus of the medial longitudinal fasciculus (NfJm) has been identified as a locomotor region in the midbrain of the carp. Nflm neurons extend axons to the spinal cord and are connected to intraspinal motor neurons and intemeurons. Physiological studies have demonstrated that there are neurons in Nflm which fire tonically only during swimming. These neurons probably drive spinal the CPGs to initiate and maintain swimming. Swimming of unrestrained goldfish can be induced by wired and wireless electric stimulation of Nflm, also supporting arguments that Nflm controls swimming in teleost fishes. The involvement of the fish cerebellum in swimming is also discussed.