Which cranial nerve regulates heart rate and gastrointestinal function?

The vagus nerve is primarily responsible for regulating heart rate and gastrointestinal function. This is due to its extensive parasympathetic innervation of various organs. The vagus nerve, also known as cranial nerve X, exerts a calming influence on the heart by slowing down the heart rate through its connection to the sinoatrial node, which is the heart's natural pacemaker. Additionally, it plays a crucial role in digestive processes, such as stimulating peristalsis in the intestines and promoting secretion of digestive enzymes, which are essential for proper digestion and absorption of nutrients.

While the other cranial nerves mentioned may have important functions, they do not have a significant role in regulating heart rate and gastrointestinal activity as the vagus nerve does. The glossopharyngeal nerve is involved in functions such as taste and swallowing, the accessory nerve primarily controls sternocleidomastoid and trapezius muscles for movement of the head and shoulders, and the facial nerve regulates facial expressions and taste sensations, but none of these are directly involved in heart rate or gastrointestinal regulation.