Lateral line

Lateral line organs are sensory organs for motion stimuli. They occur only in primary aquatilen vertebrates: Nearly all fish and permanently aquatic amphibians such as the human fish or frogs have lateral line organs. In land vertebrates ( amniotes ), they are completely absent, even if these secondary returned to aquatic life. The organs are applied to hundreds to thousands along the side of the body and in several lines on the head ( originally here). In many fish they can be as a line of pores ( = lateral line ) shown in the middle of the fuselage, hence the name. Mediated by the lateral line perception is also known as Ferntastsinn. Adequate stimuli are pressure waves that occur in a tube system if another fish above swims.

Construction principles

There are different construction principles for lateral line organs, including the Lorenzini ampules and neuromasts.

In Lorenzini ampules are jelly- filled channels that penetrate deep into the skin and grow at the ends of nerve cells in the part of the ampoules. The vials can also receive out of pressure refrigerant and chemical and electrical stimuli. Adequate stimuli are weak currents which arise for example in the muscle activity of prey.

The neuromast hair cells consist of cells that have one or more immobile cilia. It is finger -like structures, which are surrounded by jelly ( the cupula ) and protrude into the open waters. The remote from the water side of the hair cells are attached nerve cells which receive the signals when the cilia are bent by an external stimulus.

During the evolution of the lateral line has been converted to electric receptors in some fish. Some of these are used for geomagnetic navigation, the migrating fish can be so guided by the magnetic fields of the earth.

Mechanism

On both sides through a row of pores on the body. These pores lead into a channel, which is located directly under the skin. In this channel, which is filled with a gelatinous mass, extend many sensory cells, each a long Kinocilium and many microvilli. These are surrounded in clusters of a protective membrane, the cupula. The gelatinous water column in the channel is by pressure waves to vibrate, so that the processes of the receptor cells are bent in certain directions.

Without these gelatinous column of water would flow into the channels and spread it with flow directions that have nothing to do with the direction of the water pressure waves. But as the jelly column forward, backward, up, down and depressed at the same time towards the sensory cells with varying intensity. Thus, the fish perceives finest flow changes and water pressure waves as a anschwimmender enemy or an obstacle cause ( Ferntastsinn ).

Sardines use the lateral line organ for protection from predators: The fish form a huge swarm as a single large fish behaves. Any small change in motion of the neighboring fish leads to just such in the other, as even the slightest pressure differences be felt.