Let me start off with a couple of metaphors.
In the third Lord of the Rings film, a signal for help is sent from Minas Tirith to Gondor, using a chain of beacons. When the keepers of one of these beacons sees that the one next to his lit, his orders are to light his own thus passing on the chain reaction. When the last one within sight of Gondor is lit, the message that Minas Tirith wants help is received. There is nothing conveyed in the fire itself, no information within the flames, the beacons are either on or off. The only reason the beacons convey a message is that the citizens of Gondor know why that beacon would be lit.
Imagine a simple pressure sensor inside a building that is connected by a wire to an electric light on a control panel in a security room. When someone steps on the sensor it completes the circuit which sends electricity straight to the light turning it on. A label on the light says what it's connected to and where it is. So that when the light comes on, the person at the control panel knows someone is in that sector of the building. But to be more precise, he knows someone has activated that particular pressure sensor, if it wasn't labelled he would have no idea what the message meant.
My understanding of the human nervous system is that it works in the same way. Based on information I learned from children's educational programs as a child and a few bits I picked up since.
Our ears have sensors designed to respond to sound. Each and every one has a direct connection to the brain via a chain of nerve cells. When one of the sensors is sufficiently stimulated, it zaps the neuron it's connected to, this in turn causes the neuron to zap the next one and so on all the way up to the brain.
The impulses/spikes themselves contain no actual information, they are just pure electricity, every spike contains the same amount of voltage. The only reason the brain is able to interpret them is because it knows exactly where each and every chain is connected to. When the impulse reaches the brain it knows it comes from a sensor in the ear that is responsible for a particular level of sound, the brain takes these signals and translates them into the sounds we hear. Nerve cells work something like binary, they are either on or off with nothing in between. The frequency of the spikes going along the chain indicates how intense the sound is. If the brain didn't know where that chain was connected to then the signal could mean absolutely anything.
This is supported by the condition known as synaesthesia where, because "wires are corssed" in the brain there are people who hear colour or taste music.
My questions are, is my reasoning correct? Is this exactly how nerves and perception work? Has this been scientifically proven beyond a doubt? Is there something within the impulses that contains additional information? Are the workings of the nervous system debated in scientific circles? I've been told we've never been able to plug an eyeball or any other kind of human sensory device into a computer so we've never been able to examine it as it's working, is this true?
But most of all, does this mean there are things our senses cannot detect? I already know there are things beyond our range of vision and hearing and the brain blurrs then together. What I mean is this...
I know that we have different senses in our ears that are designed to respond to higher or lower sounds. Say we have a sensor that responds to a level 1 sound (I don't know the unit of measurement for sound) and next to it is a sensor that responds to a level 2 sound. What happens if we try to hear a 1.5 sound? Is it not detected by the ear because we don't have sensors in that range?
Can we only sense something if we have a sensor for it and are those sensors only built to sense one ultra specific thing?