Answer
The signal lasts longer in a reverberating circuit because input is repeatedly renewed by axon collaterals from later neurons to earlier neurons in the pathway.
Work Step by Step
If a circuit had the following path : Input-V>X>Y>Z--Output. The signal would cease propagating when the initial Input from neuron "V" ceased. However, if every time "Y" fired, it not only sent a signal forward to "Z" but also a signal back to "V", the signal would be renewed over and over, and be propagated for a long time--even when the source of the original input into "V" ceased. This is the way a reverberating circuit works to prolong transmission of a stimulus. This stimulus keeps reverberating in this kind of circuit until one (or more )neuron stops functioning, or an inhibitory stimulus from somewhere else intervenes. In the process of inhalation, the diaphragm and the intercostal muscles are stimulated by reverberating stimuli.
