Which phenomenon describes the release of acetylcholine by neurons that decreases heart rate?

The release of acetylcholine by neurons that decreases heart rate is best described by neural control. Neural control specifically refers to the regulation of physiological processes by the nervous system. In this context, the autonomic nervous system (ANS), particularly the parasympathetic division, plays a vital role in modulating heart rate. When acetylcholine is released from vagus nerve endings, it binds to receptors on cardiac muscle cells, leading to a decrease in heart rate, a process known as negative chronotropy.

This phenomenon is part of the direct communication system of the nervous system, where signals are transmitted across synapses to exert immediate effects on target organs. This is distinct from other forms of regulation, such as endocrine control, where hormones are released into the bloodstream to act on distant sites, or paracrine control, which involves local signaling to nearby cells. Therefore, the release of acetylcholine clearly aligns with neural control mechanisms.