Single neuron summation

The network architecture of a PNN (Figure 8.1) is similar to that of a GRNN, except that its summation layer has a neuron for each data class and the neurons sum all the pattern neurons output corresponding to members of that summation neuron s data class to obtain the estimated probability density function for that data class. The single neuron in the output layer then... 

As previously mentioned, a single action potential at a single synapse results in a graded potential only an EPSP or an IPSP. Therefore, generation of an action potential in the postsynaptic neuron requires the addition or summation of a sufficient number of excitatory inputs to depolarize this neuron to threshold. Two types of summation may occur ... 

Temporal summation occurs when multiple EPSPs (or IPSPs) produced by a single presynaptic neuron in close sequence exert their effect on membrane potential of the postsynaptic neuron. For example, an action potential in the presynaptic neuron produces an EPSP and partial depolarization of the postsynaptic neuron (see Figure 5.2). While the postsynaptic neuron is still depolarized, a second action potential in the presynaptic neuron produces another EPSP in the postsynaptic neuron that adds to the first and further depolarizes this neuron. 

Figure 5.2 Temporal summation. Multiple excitatory postsynaptic potentials (EPSPs) produced by a single presynaptic neuron in close sequence may add together to depolarize the postsynaptic neuron to threshold and generate an action potential.

Convergence occurs when the axon terminals of many presynaptic neurons all synapse with a single postsynaptic neuron. As discussed previously, spatial summation of nerve impulses relies on the presence of convergence. Divergence occurs when the axon of a single presynaptic neuron branches and synapses with multiple postsynaptic neurons. In this way, activity in a... 

Motor imit potential (MUP) Spatial and temporal summation of aU single-fiber potentials innervated by the same motor neuron. Also referred to as the motor unit action potential (MUAP). 

Figure 3.2 (See color insert.) Schematic overview of insect antennal structures and possible modes of elec-trophysioiogicai measurements. Antennae are adorned with many sensillum types, each housing olfactory receptor neuron (ORNs) of various sensitivities as defined by the olfactory receptors they express. Approximate summated responses from many/all sensilla can be recorded in the fonn of voltage deflections, termed electroantennogram (right), or individual ORN responses can be measured by penetrating a single sensillum (bottom).

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