Arthropods nerve cells

The simplest mechanoreceptors are morphologically undifferentiated nerve endings found in the connective tissue of skin. In many mechanoreceptors there have evolved accessory structures whose function is the efficient conversion of mechanical energy to electrical energy in the receptor cell. Examples are Pacinian corpuscles, in which the sensitive ending is covered by a cap-sule, muscle stretch receptors, in which the mechanically sensitive endings are associated with specialized muscle fibers, and the hair-like sensilla in the exoskeletons of arthropods (Figure 45). Elaborated accessory structures used to detect and analyze sound waves are found in the vertebrate middle and inner ear. ... 

Tetrodotoxin (TTX) is a good example of a compound that has recently assumed a prominent rdle in biophysical investigations of nerve and muscle function it selectively prevents the opening of membrane channels for Na-ions that would normally occur during depolarization. TTX has become an important tool in the dissection of the excitation process of electrically excitable cell-membranes into phases involving separate and successive activation of ion-selective channels. Use of TTX has already helped establish that there are many types of nerve and muscle cells in which spike potentials are not accompanied by an inward current of sodium ions but of calcium ions. TTX has been successfully employed in studies on nerve and muscle cells of many arthropods and molluscs as well as of vertebrates —its mechanism of action was found to be identical in all cases. 

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