How does my brain know that a sensation is coming from my finger, as opposed to my foot? Don’t all the nerve endings eventually join into a single point of entry into my brain?


Let’s say I touch a piece of hot apple pie. My finger knows it’s warm. The sensation from my finger travels to my wrist, where the nerve endings from my fingers / hand join up. Then the sensation travels up my arm, to my torso, to my spine, where all the other nerves from my feet and hands and stomach and legs all join.

Are there individual paths of fibers that remain distinct all the way into the brain? is there a unique ‘signature’ that lets the brain know where a certain nerve signal is coming from?

In: Biology

>Are there individual paths of fibers that remain distinct all the way into the brain?

Yes, basically. There is a small amount of convergence, which is why if you prick yourself on your skin with two pins that are very close together, it feels like one.

However, for the most part, these pathways (called ‘labelled lines’, sometimes) remain separate all the way to the brain. Just like a woven rope seems like one strand, but is in fact thousands of tiny strands banded together. It’s the same with our neural pathways.

They all end up in slightly different places on the surface of the brain. There’s actually a ‘map’ of this sensory layout. Certain parts of our body are overepresented on this map based on their size (fingers, lips, etc). That means that they typically have much finer discriminatory sensory capacity than others.

[Here’s an example of that map]( You can see that there’s only a little space for the legs, shoulder, etc, but hands get a lot more!

The fibers don’t just stay distinct, there are individual single cells conducting the stimulus. There’s a single cell travelling all the way down from the brain to some part on the extremities of the body. This gets even more crazy when you consider this is true in blue whales and would have been true for dinosaurs too….which means various neuron cells have lengths measured in tens of meters