Structural and functional organization of the lateral line system of sharks

Abstract

The lateral line sense organs of sharks include ampullae of Lorenzini and neuromasts. Each of these two classes of receptors is highly specialized and therefore can be expected to biologically respond to one specific modality of stimulus of minimal threshold intensity. Current anatomical, electro-physiological and behavioral evidence indicates that the ampullae are organized to respond to very weak DC and low frequency AC electric fields that originate from external sources in the environment and that this information is used in the detection of prey. Neuromasts consist of canal receptors and pit organs and are mechanoreceptors that are sensitive to water movements caused by external sources as well as the animal's own swimming movements. There is no convincing experimental evidence of the behavioral role that neuromasts play in the life of sharks, but they can orient toward a source that causes water displacements and perhaps use the neuromast system in the coordination of locomotor activity.Ampullae and neuromasts are innervated by different components of the lateral line nerves that project to special terminal areas within the central nervous system. The dorsal root of the anterior lateral line nerve, which is believed to carry nerve fibers from the ampullae of Lorenzini exclusively, enters and terminates within the anterior lateral line lobe of the medulla. Neuromasts (canal and pit organs) are innervated by the ventral root of the anterior lateral line nerve and posterior lateral line nerve, which project to the posterior lateral line lobe (nucleus medialis) of the medulla and, in addition, distribute to the eminentia granularis of the cerebellum, superior and inferior lobes of the auricle, and to the spinal cord. There is no apparent overlap between those central terminal fields that receive fibers from electroreceptors and those that receive fibers from mechanoreceptors nor with the central terminal field of VIIIth nerve neurons. This supports the contention that different functional classes of lateral line receptors are specialized to perform a particular function, but the central coordinating and integrating mechanisms are unknown. © 1977 American Society of Zoologists.