FIGURE 1.2-7 A finite RCG transmission line model of a myelinated axon. One node of Ranvier is shown to the left with (active) voltage-dependent gNa and gK conductances; the other four linear RCG elements model the electrical properties of the axon under the myelin bead. Six or seven of the units shown can be connected in series to simulate the saltatory conduction illustrated in Figure 1.2-6. (Eight ODEs are needed to simulate one unit, four for the HH node and four for the myelinated axon.)
effect is felt on the next neuron in the chain of communication, the postsynaptic neuron. Depending on the type of synapse, the postsynaptic neuron can be brought closer to firing its own spike(s), or inhibited from firing.
An interneuron or motoneuron generally has many input synapses, providing redundancy, and, as will be shown, noise reduction in the information transfer process. Generally, synapses terminate the branches of the terminal arborizations of the axon of the presynaptic neuron. Synapses may make contact with dendrites (axodendritic synapses), the soma (axosomatic synapses), and even with the boutons of the postsynaptic neuron (axo-axonic synapses).
There are two types of synapses: chemical and electrical. Most synapses are chemical; however, there are examples of electrical coupling between neurons where speed and reliability of transmission are required. In Table 1.3-1, properties of chemical and electrical synapses are summarized:
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