Although the leg is a big part of the body ,only a small area in the sensory region is sensitive to stimuli from it .Explain why this is so ?

Question

We have to relate it to terminology with the nervous system and anatomy of the brain 

Answer 1

Your question appears to be referring to the relative surface area dedicated to the leg on the brain's sensory cortex. Indeed, physically large areas of the body may be relatively poorly represented there. The reason for this is that fewer sensory neurons are dedicated to these areas. The leg is one such example. The back is another.

The body is governed by the evolutionary drive to be extremely economical with resources and that includes sensory neurons. Thus, we dedicate more neurons to the most critical areas that are likely to give us far more important information, such as the eyes, lips, tongue, hands, and gastrointestinal tract, and genitals. In all of these areas we see a much greater number of sensory nerve endings per square inch than on the skin of the legs or on our backs.

If you search online for an image of the "human sensory homunculus" you will find a photograph of a bizarre-looking and very distorted model of a man. I find this image very memorable and useful for understanding how the body is represented in the brain. And if you really think about it, this is exactly how we perceive our bodies, thinking of ourselves as mostly being a face and hands!

I hope this helps your studies! Best of luck.

Dr. Victor P.