About the Sensory, Motor Homunculus
(See attached img)

DESCRIPTION:
Sensory and motor pathways are topographically organized according to their level of sensitivity and control, respectively.

QUESTION: how do we read this? As in, how do we know which one is more sensitive from the image?

Question

About the Sensory, Motor Homunculus
(See attached img) 

DESCRIPTION:
Sensory and motor pathways are topographically organized according to their level of sensitivity and control, respectively. 
 
QUESTION: how do we read this? As in, how do we know which one is more sensitive from the image?

anonymous · Answer

attachment

blues · Answer

If it appears bigger, then it is more sensitive or you have finer control of it. So for example, the lips appear huge in the sensory one because they are very sensitive; the forearm appears smaller because it is less sensitive.

I was always a little unclear about whether there is any quantitative basis for these drawings - as when whether they actually count the number of sensory or motor neurons in a particular region or whether they just ballpark it.