Rearrange Alphabets ‘P N E I S’ and Form Name of an imp. Human Body Part?

An engineer said: When I was young,

I decided to go to medical.

At the entrance exam,

we were asked to rearrange the alphabets

“P N E I S”

and form the name of an important human body part.

which is most useful when straight.

.

.

.

Those who answered SPINE are doctors today,

While the rest are Engineers.