I think you are asking for the body part that identifies the messages of the senses; that's the brain.
every part of the body senses change, but if the question means which part senses first, the answer is the heart.
your tongue
Main body
nerves
Central Nervous system.
cerebral cortex
the brain cells
host address
Specialized cells that send messages from one part of the body to another.
You can't tell where that part of the body is (except by other senses, such as touch and sight).
The brain
Nerve tissue