Final answer:
The parasympathetic nervous system is responsible for lowering the heart rate, functioning opposite to the sympathetic system and operating via the vagus nerve.
Step-by-step explanation:
The component of the nervous system responsible for lowering the heart rate is the parasympathetic nervous system. This system is involved in the 'rest and digest' state of the body’s functions, in contrast to the 'fight or flight' state that is governed by the sympathetic nervous system. It operates via the vagus nerve, which releases the neurotransmitter acetylcholine that acts on the heart to decrease the heart rate. When the vagal (parasympathetic) stimulation is high, it outbalances the sympathetic stimulation, leading to a slower heart rate, commonly experienced when at rest.