Arthropods have provided several important models of mechanotransduction. In contrast to vertebrate somatic receptors, arthropod cuticular receptors have cell bodies located close to their sensory endings, facilitating electrophysiological and morphological studies. Spider slit sensilla provide a useful general model of spiking mechanoreceptors in which the neurons can be visualized during experiments, and are easily accessible to chemical changes in the bathing saline. Electrical recording, including single-electrode voltage-clamp is possible during simultaneous mechanical stimulation of the slits, which allows the receptor current, receptor potential and action potentials to be measured. The neurons also receive peripheral efferent innervation from the CNS that affects the mechanosensory processes at several stages, providing an important model of sensory neuromodulation. Spiders have many slit sensilla, but the VS 3 organ in the spider patella has been most widely used (Barth 1971; French et al. 2002). VS 3 neurons respond to stress in the cuticle with rapidly adapting action potentials. Although their physiological functions are unknown, they probably act primarily as vibration detectors. The spider sensory world has a large mechanical component, and vibration is clearly important for functions such as prey detection and courtship. Receptor current in VS 3 neurons is highly selective for sodium ions and can be increased by extracellular acid, suggesting that the mechanotransduction channels are members of the Acid-sensitive/Degenerin/Epithelial sodium channel family. Immuno-labelling with antibodies to the C. elegans MEC 4 protein supports this hypothesis. Several lines of evidence suggest that the mechanotransduction channels are located at the tips of the sensory dendrites, and that action potentials are initiated in the same region. The number of active mechanotransduction channels per neuron has been estimated to be five hundred. VS 3 neuron membranes have a voltage-sensitive T type calcium current that activates when the neurons are depolarized above about 50 mV (normal resting potential is about 70 mV). Antibody labelling to the CaV3.1 encoded α1G sub-unit indicated that voltage-activated calcium channels are widely distributed over all major regions of the neurons. Mechanically-driven receptor current does not depolarize the neurons enough to activate a calcium current, but action potentials cause large increases in internal calcium concentration. Calcium elevation, in turn, reduces receptor current, possibly by binding to mechanotransduction channels, with an estimated stoichiometry of two calcium ions per channel. This indicates that calcium concentration serves as a feedback regulator of mechanical sensitivity. Mechanical information is transmitted to the CNS by action potentials. Quantitative measurements of information capacity and action potential entropy as a function of firing rate indicate that VS 3 neurons have a low level of inherent noise, and that information transmission is limited primarily by the maximum firing rates that the neurons can achieve.