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Conduction of impulses in myelinated axons has been studied by a new method of computer simulation. The contributions of nodal and internodal characteristics and parameters were examined. Surprisingly, the conduction velocity, theta, was found to be quite insensitive to the nodal area or the exact description of its excitable processes. The conduction(More)
Changes in redox status are a conspicuous feature of immune responses in a variety of eukaryotes, but the associated signalling mechanisms are not well understood. In plants, attempted microbial infection triggers the rapid synthesis of nitric oxide and a parallel accumulation of reactive oxygen intermediates, the latter generated by NADPH oxidases related(More)
It has been argued theoretically and confirmed experimentally that conduction velocity (theta) should be proportional to nerve fibre diameter for myelinated fibre tracts, such as normal peripheral nerve, exhibiting 'structural' similarity'. In some axons, however, the nodes of Ranvier are more closely spaced than in normal peripheral nerve. Analytic(More)
Signalling by members of the Hedgehog family of secreted proteins plays a central role in the development of vertebrate and invertebrate embryos. In Drosophila, transduction of the Hedgehog signal is intimately associated with the activity of protein kinase A and the product of the segment polarity gene patched. We have cloned a homologue of patched from(More)
Classical conditioning procedures instill knowledge about the temporal relationships between events. Conditioned stimuli (CSs) are regarded as predictive signals and triggers for action. The unconditioned stimulus (US) is the event to be timed. The conditioned response (CR) is viewed as a prediction of the imminence of the US. Knowledge of the elapsed time(More)
A study was made of synaptic transmission between the four median photoreceptors of the giant barnacle (Balanus nubilus) and their post-synaptic cells (I-cells). Simultaneous intracellular recordings were made from the presynaptic terminal region of a photoreceptor and from the soma of an I-cell. The photoreceptor's membrane potential provided feed-back to(More)
In the preceding paper (Moore & Westerfield, 1983) the effects of changes in membrane properties and non-uniform geometry on impulse propagation and threshold parameters were investigated. In this paper the contributions of these and other parameters to the site of initiation of an impulse were determined by computer simulations using the Hodgkin-Huxley(More)
1. The propagation of action potentials through the branching regions of squid axons was examined experimentally and with computer simulations over a temperature range of 5-25 degrees C. 2. Above a critical ratio of postbranch to prebranch diameters, propagation of an action potential failed. The value of this critical ratio is very sensitive to temperature(More)
1. Ionic currents associated with the invasion of an action potential into the motor nerve ending of the lizard, Anolis carolinensis, were measured with a focal extracellular electrode at several locations along the nerve ending. 2. These experimentally observed currents could be matched with computer simulations of action potential propagation into the(More)
The squid giant axon was used as a model system in which to determine the independent contributions of membrane excitability and diameter changes to threshold parameters and propagation of action potentials in inhomogeneous regions. The membrane excitability of a segment of an axon was altered by changes in the bathing solution, while its effective(More)