In this book, we mainly focus on the dynamic features and mechanisms of excitable neuron and neuronal networks in the detection of weak signals by using Hodgkin-Huxley (HH) model. We have studied the effect of external noise and signal frequency on the collective dynamical behaviors of the neuronal system. We have observed the existence of the intrinsic oscillation and the frequency-dependent impendence of the ionic channels of HH model. These features provide the HH systems interesting behaviors like resonance and frequency preference, which can enable the neuronal systems serve as a band-filter and a signal amplifier. That is, the signal with frequency around that of the intrinsic oscillation can be efficiently processed and amplified. An effective sensitive frequency region is found in a range of 30-100 Hz.