Table 41.1 summarizes some of the best known neurotransmitters and their effects. Synaptic Shut Down Synaptic responses are turned off by clearing the synapse of neurotransmitter through diffusion the use of enzymes or by active transport into nearby cells. Neuron Circuits Neurons work in circuits and the simplest circuit has two neurons. This is termed a monosynaptic circuit . When more than one synapse is involved the circuit is polysynaptic .
More complex circuits have interneurons that communicate with additional neurons.
The knee jerk reflex is a simple two-neuron circuit controlling a monosynaptic reflex. It is associated with a polysynaptic reflex. These relationships are illustrated in Figure 41.19 .