I’ve been looking at the above image for years. You have too. There is almost nothing left to notice…but I just noticed how hollow the homunculus is.
There is no representation of your organs anywhere to be found! Are you trying to tell me that I cannot “feel” the inside of my body?!(in the simplest sense of the word)
I’m walking around with a brain and a liver and a spleen but … how do I feel them? It seems as though I can feel them, but if I really search for them in my mind… nope, not there.
Let’s start here:
We have all seen pictures of referred pain like this.
They seem overly complex and confusing. “You mean my kidney can refer and make my shoulder hurt?” Well, yes. “You mean my abdominal aorta can make me feel low back pain?” Well, yes.
The common version of explaining this is that the general visceral afferent nerves that innervate these organs (heart for example) hitch a ride with peripheral somatic sensory nerves and the signals get mixed in the dorsal horn of the spinal cord (mimicking shoulder pain). Yes that’s true, but the real reason you feel your shoulder during a heart attack is that you just can’t feel your heart. There is no place in your brain to alert yourself to heart danger, peripheral sensors or no!
It’s not that your heart made your arm hurt, it’s that we are incapable of feeling it any differently. We are limited.
If a tree falls in the forest and no one is there to hear it, does it make a sound? If a duodenum screams out in irritation, is there a receptor area to take the input?
So cerebral body sensory areas are stimulated via this peripheral phenomenon… and we gain filtered information about our visceral systems. We must make inferences. We need to correlate clusters to get an idea of our current state.
We have no first hand information about our innards. Crazy.
We are indeed hollow, a deuterostome, a tube…sensorily speaking.