Neuromasts

Neuromasts are mechanosensory organs that form part of the lateral line system in most aquatic vertebrates, including most fishes and many amphibians. They detect water movements and vibrations in the surrounding medium, enabling behaviors such as obstacle avoidance, orientation, and prey detection. A neuromast is a discrete sensory unit composed of hair cells, supporting cells, and a gelatinous cap called the cupula. Hair cells possess apical bundles of stereocilia and a single taller kinocilium. Deflection of the hair bundles toward or away from the kinocilium alters the hair cells’ receptor potential and drives activity in afferent neurons that innervate the neuromast via the lateral line nerve.

There are two principal classes: superficial (free-standing) neuromasts that lie on the skin surface, and canal neuromasts located within the fluid-filled lateral-line canals. Canal neuromasts sense flow generated by movement of endolymph in the canals, whereas superficial neuromasts respond directly to water flow over the body surface. Each neuromast is polarized, meaning most hair cells are oriented so that the direction of deflection corresponds to specific directional sensitivity within the body. The information from many neuromasts is integrated in the brain to provide a map of water movement around the animal.

In fishes and amphibians, neuromasts can regenerate after injury. The lateral line system is largely absent in adult mammals, though vestigial or developmental precursors exist in some species, making neuromasts primarily a feature of non-mammalian vertebrates.