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3 results

  • Chapter 7 - The Synapse

  • David Sterratt, University of Edinburgh, Bruce Graham, University of Stirling, Andrew Gillies, Psymetrix Limited, Gaute Einevoll, Norwegian University of Life Sciences (NMBU), David Willshaw, University of Edinburgh
  • Book:
    Principles of Computational Modelling in Neuroscience
    Published online:
    07 October 2023
    Print publication:
    05 October 2023, pp 185-209

  • Summary

    This chapter covers a spectrum of models for both chemical and electrical synapses. Different levels of detail are delineated in terms of model complexity and suitability for different situations. These range from empirical models of voltage waveforms to more detailed kinetic schemes, and to complex stochastic models, including vesicle recycling and release. Simple static models that produce the same postsynaptic response for every presynaptic action potential are compared with more realistic models incorporating short-term dynamics that produce facilitation and depression of the postsynaptic response. Different postsynaptic receptor-mediated excitatory and inhibitory chemical synapses are described. Electrical connections formed by gap junctions are considered.

  • 8 - Synaptic Transmission in the Nervous System

  • Christopher L.-H. Huang, University of Cambridge
  • Book:
    Keynes & Aidley's Nerve and Muscle
    Published online:
    07 November 2020
    Print publication:
    19 November 2020, pp 106-120

  • Summary

    Central nervous system function depends on synaptic transmission involving either chemical-transmitter-mediated or direct electrical coupling between neurones. Transmitter activation of excitatory and inhibitory synapses respectively produce postsynaptic membrane depolarisation and hyperpolarisation in turn increasing or decreasing likelihoods of action potential firing by the targetted neuron. Further variants of neuron-neuron interactions include inhibition at the level of presynaptic terminals and G-protein dependent slow synaptic potentials. Some central nervous system synapses additionally show longer-term potentiation or depression phenomena with repeated activity produced by intracellular signaling mechanisms; these may underly memory. Finally, direct electrical synaptic connections between cells can synchronise firing between neurones. Release of K+ and transmitter glutamate by central neurones during intense electrical activity potentially perturbs their extracellular environment. This is normally corrected by transport activity in their closely related glial cells. Malfunctions in this buffering function predisposes to cortical spreading depression phenomena clinically associated with migraine aura.

  • Role of GABAA-mediated inhibition in controlling the responses of regular spiking cells in turtle visual cortex

  • JAIME G. MANCILLA, PHILIP S. ULINSKI
  • Journal:
    Visual Neuroscience / Volume 18 / Issue 1 / January 2001
    Published online by Cambridge University Press:
    10 April 2001, pp. 9-24

  • The visual cortex of freshwater turtles contains pyramidal cells, which have a regular spiking (RS) firing pattern, and several categories of aspiny, inhibitory interneurons. The interneurons show diverse firing patterns, including the fast spiking (FS) pattern. Postsynaptic potentials (PSPs) evoked in FS cells by visual stimulation of the retina reach their peak amplitudes as much as 200 ms before PSPs in RS cells (Mancilla et al., 1998). FS cells could, consequently, control the amplitudes of light-evoked PSPs in RS cells by producing disynaptic, feedforward inhibitory postsynaptic potentials (IPSPs) that overlap in time with geniculocortical excitatory postsynaptic potentials (EPSPs). Since FS cells receive recurrent, excitatory inputs from RS cells, they could also control the amplitudes of light-evoked PSPs in RS cells via polysynaptic, feedback inhibition. The in vitro geniculocortical preparation of Pseudemys scripta was used to characterize the temporal relationships of EPSPs and IPSPs produced in RS cells by electrical activation of geniculate afferents and by diffuse light flashes presented to the retina. GABAA receptor-mediated inhibition was blocked using extracellular application of bicuculline (3.5 mM) or intracellular perfusion of picrotoxin (1 μM) in individual RS cells. Electrical stimulation of thalamic afferents produced compound PSPs. Blockade of GABAA receptor-mediated IPSPs with either bicuculline or picrotoxin provided evidence for both early and late IPSPs in RS cells. Analysis of the apparent reversal potentials of light-evoked PSPs indicated the existence of early IPSPs during the first 140–300 ms following light onset. Light responses of cells perfused with picrotoxin diverged from control light responses at about 300 ms after light onset and had maximum amplitudes that were significantly different from control light responses. These experiments indicate that the responses of RS cells to both electrical and natural stimulation of geniculate afferents are controlled by both early and late IPSPs, consistent with activation of both feedforward and feedback pathways.