Which cranial nerve provides parasympathetic innervation to the heart?

The vagus nerve is the cranial nerve that provides parasympathetic innervation to the heart. It is the tenth cranial nerve (CN X) and plays a crucial role in the autonomic nervous system, particularly in regulating heart rate. The vagus nerve extends from the brainstem down into the thoracic and abdominal cavities, influencing various organs, including the heart.

By releasing neurotransmitters such as acetylcholine at the heart's pacemaker cells, the vagus nerve slows the heart rate, counterbalancing the sympathetic nervous system's stimulation, which tends to increase heart rate and contractility. This balance is vital for maintaining homeostasis and appropriate responses to physiological demands.

The other cranial nerves listed do not have the same primary role in coronary innervation as the vagus nerve. The accessory nerve primarily controls shoulder and neck muscles, the facial nerve is involved in facial expression and taste sensation, and the glossopharyngeal nerve has roles in taste and the swallowing reflex, with some contributions to parasympathetic functions, but not as the primary innervator for the heart.