The Nervous System is mainly divided into two parts which are the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).
The nerve fibers that send impulses to slow the heart's rate of contraction belongs to the PNS, particularly under the Autonomic Nervous System. This is where impulses can't be directly controlled by the brain, and the body does these things automatically in order to adapt to a particular situation.
