Imagine you're a neuron

Imagine you're a neuron.  You have hundreds of inputs and a single output.  Let's say that the inputs are temperature sensors from all over the body.  You know which input corresponds to which part of the body.  You can pass a single input along, or you can define thresholds that say "if X of my inputs fire, I will fire".

Your owner wakes up on a cold, cold morning.  During sleep, you have been silenced by a flood of sleep hormones that dampened all but the strongest inputs, the ones that signal something catastrophic.  But upon waking, you get a signal from somewhere in the memory system that starts registering extreme cold.  This is not an actual physical input; it is a recording, being played to you at high priority for you to pass on.

This is your brain running the wake-up program.  At least, it's my brain.  My higher-level thinking is basically: I'm in this warm bed and my alarm is going off.  If I get up, it'll be cold until I get to the shower.  Therefore, I want to stay in bed, therefore, hit the snooze button.

Now I don't actually feel cold, but I anticipate it, which runs through pretty much the same circuitry as actually feeling cold.  So back at the neural level, this neuron that reports on the temperature of my body is getting a phantom (anticipatory) "it's cold" signal and passing it on to what I assume is some kind of a conscious-level circuit, where I can make a decision about what to do about the cold.

Now let's say I have some self-control and decide to brave the cold.  My neuron will initially register the temperature change, but my higher mind will send an inhibitory signal back to me that's basically "yes, I know it's cold, but it's not dangerous so you don't have to warn me about it", and I'll squelch my inputs.

This is the life of a neuron.  It's a lot like what Homer Simpson is supposed to do at his job, really.  You've got a control panel in front of you that's all the things you're supposed to be monitoring, and you're supposed to report to your superiors if anything looks wrong.  Most of your job is knowing what to ignore, because your manager gets really mad if you make too much noise for no good reason.  However, the safety of the whole system is incumbent on you alerting when things look out of whack.

A neuron is essentially a filter with a bunch of different modes.  The mode is determined by the levels of hormones floating around; in a physically dangerous situation, your visual system may become more sharp and focused, while your pain receptors may be extremely muted.  There are probably a small, enumerable set of "modes" that different neural circuits can be in.  The systems, when in good health, should operate in homeostasis: stress mode leads to the macroorganism taking actions that lead it to safety.