The slow EPSP in Figure 26.11 was evoked by repetitive shocks (5 Hz) applied to the fiber tract for 5 seconds. Slowly activating depolarization of the membrane potential with a time course lasting longer than 2 minutes after termination of the stimulus is apparent. Repetitive discharge of action potentials reflects enhanced neuronal excitability during the EPSP. The record shows hyperpolariz-ing after-potentials associated with the first four spikes of the train. As the slow EPSP develops, the hyperpolarizing after-potentials are suppressed and can be seen to recover at the end of the spike train as the EPSP subsides. Suppression of the after-potentials is part of the mechanism of slow synaptic excitation that permits the neuron to convert from low to high states of excitability.
Slow EPSPs are mediated by multiple chemical messengers acting at a variety of different metabotropic receptors. Different kinds of receptors, each of which mediates slow synaptic-like responses, are found in varied combinations
Enteric nervous system
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