Nerve impulses are sent to slow the heart's rate of contraction. the nerve fibers sending these signals will most likely belong to which division of the nervous system

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. 

The answer to that question is a

By water evaporation from the leaves is created a negative pressure at the top of the tree that promotes the ascension  of the water through channels that are called xylem. there are also two molecule forces that are involved: the intra-water molecules cohesion (water molecules stick to each other) and the adhesion when the water molecules stick to the channels they are running in. this is what enables water to go from the roots to the top of a tall tree.