Our neurons not only transmit electrical currents but also use various chemical nerve transmitters . Glutamate is a major transmitter involved in learning. The transmitters do not act directly but through receptors on the surface of the neuron. There are other receptors which act only chemically, the metabotropic receptors. Figure 8, page 11, shows the location of our substantia nigra and that of rats.
Many viruses can exchange genes with one another.
These genes lie on special structures called plasmids , which have played an important role in genetic engineering. A pS is a picoSiemens .