Sódio e potássio em Delanda (2011)
The standard model of neurons places the manipulation of gradients of metallic ions, potassium or sodium ions, for example, at the heart of their functioning. Manipulating these chemical gradients – keeping potassium at high concentrations inside the cell and at low concentrations outside of it – produces yet another gradient, one of electrical potential. The key to the conversion of one gradient into another is the selective permeability of a neuron’s membrane to metallic ions: as membrane permeability changes ions flow in and out of the cell creating variations in the gradient of electrical potential. Neurons use these smooth low-level variations to record the electrical signals acting as their input. Producing an output involves changing the electrical gradients from continuous to discrete, transforming them into a chain or train of practically identical electrical spikes. This spike train is used to produce a chemical signal that, when received by other neurons, increases the permeability of their membranes if the chemical substances are excitatory or decreases it if they are inhibitory. [Nota de rodapé 2: Ronald J. MacGregor and Edwin R. Lewis. Neural Modeling. (New York: Plenum Press, 1977). p. 21–30.] To provide a mechanism for habituation in simple creatures all we need to assume is that the supply of an excitatory substance in a sensory neuron becomes progressively depleted after successive stimulations, so that less and less of this substance crosses the gap to affect the permeability of a motor neuron’s membrane leading to a decrease in its response. A similar mechanism can account for sensitization if we add a second sensory neuron interacting with the first causing it to increase production of the excitatory substance arid therefore the amount of the latter that reaches the motor neuron. [Nota de rodapé 3: John T. Bonner. The Evolution of Culture in Animals. (Princeton: Princeton University Press, 1980). p. 113.] (Delanda 2011:76-7)
DELANDA, Manuel. 2011. Philosophy and Simulation: The emergence of Synthetic Reason. Londres: Bloomsbury Academic.