Integration and control: the nervous system
The complexity of fish behaviour and information processing indicates high levels of neural, anatomical and functional organization. Neural cells are conducting neurons and neuroglia with putative support and physiological roles. Neuronal conduction, synaptic transmission, reflexes and neuropils are factors in integrative activity and information processing. Fish nervous systems are organized into central (brain and spinal cord) and peripheral (including autonomic) components. Interestingly the structure and function of the fish optic tectum have been considered comparable to those of the tetrapod cerebral cortex. Also of interest are the bilaterally paired large Mauthner fibres in the teleost central nervous system, which mediate startle responses. The autonomic nervous system in fish occupies a pivotal position amongst vertebrates, including uncertainty about the existence of a posterior parasympathetic component. The trend is to regard it in terms of spinal autonomic (sympathetic) cranial autonomic (parasympathetic) and enteric systems. Accounts of the autonomic control of individual effector systems are included.