Every day, we experience different types of sensory stimulus, like heat, pain, cold, etc. However, in each case, the transmission of the stimulus to the brain through the neurones is carried on in the same way: through propagated depolarisation and repolarisation in axons, while through the release of acetylcholine at the synapses.
So, how does the different sensory stimulus differ if they are transmitted the same way? (I mean to say that how does the nerve signals differ for two different kinds of stimulus?)
Let's put the question simply:
How do two nerve signals originated from two different stimuli differ? If they do not differ, then how does the brain differentiate between different nerve signals if they are all alike? How does it understand what nerve signal carries what message?