This is how the shark monitors its swimming direction, localize vibrations in the water and detect water currents (Taylor and Taylor 1986). The nerve impulses can also be carried in the opposite direction toward the hair cell sensory organs. These impulses inhibit the lateral line sense cells whenever the shark makes and violent movements such as escaping or attacking (Gold and Springer 1989).
The acoustic sense of the shark is similar to the lateral line system. Sharks can hear sounds within a human's hearing range and, using their lateral line, they can also detect low frequency vibrations such as those make by struggling or wounded fish. Sharks have two inner ears, one on each side of the head. The inner ears contain canals, which are probably used in motion detection and they also contain vibration sensors that work with the lateral system (Taylor and Taylor 1986).
Eyes and Vision.
Sharks eyes very greatly from species to species, in size and shape. However the basic structure is a laterally compressed version of the same eye most vertebrates have. Sharks have a large proportion of rods, which are highly sensitive to changes in light intensity, making sharks sensitive to contrasts of light and shadow (Cohen and Gruber 1985). Generally the lens is spherical and held in place by ligaments on the top and muscles from below. The pupil in the eyes of some sharks (requiem sharks such as tiger sharks and reef sharks), contrary to popular belief, may open and shut quite rapidly. In contrast to mammals the lens cannot change in shape to focus. To what extent sharks are actually capable of focusing is not yet known, but recent studies are showing that at least a few sharks do have the ability to move their lens backward and forward to better focus on an object (Gold and Springer 1989). What is known though is that sharks can maintain a constant visual field and nearly panoramic vision even when they twist and turn, due to prominent muscles called protractor lentis that can effectively rotate the eyes (Taylor and Taylor 1986).
