The Biophysics of the Fish Lateral Line

Abstract

The fish lateral line system is unique in its ability to sense water flow with two types of receptors, the canal neuromast (CN) and superficial neuromast (SN). Both include mechanosensory hair cells in the skin that are coupled to an extracellular cupula, which is deflected by flow. Differences in the biophysics of these receptors cause them to detect distinct features of a stimulus. CNs are recessed within channels and possess hundreds of hair cells and a cupula that deflects as a rigid body. These features facilitate sensitivity to flow acceleration with low-pass filtering. The cutoff frequency for this filter is in the hundreds of Hertz, which allows the CNs to respond to the rapid changes in flow from a variety of biological stimuli. In contrast, SNs possess tens of hair cells and an elongated cupula that protrudes from the surface of the body. These receptors sense the velocity of flow with low-pass filtering with a cutoff frequency in the “tens” of Hertz. This allows for sensing the velocity of biological signals with high fidelity. Although CNs are more than an order of magnitude more sensitive, SNs maintain sensitivity to stimuli at high intensity. Therefore, the two receptors encompass distinct regimes of stimulus intensity and frequency.