Which nerve is involved in regulating heart rate and digestive functions?

The vagus nerve plays a crucial role in regulating heart rate and digestive functions as it is a major component of the parasympathetic nervous system. This nerve extends from the brainstem down to the abdomen, influencing various organs along its path.

In terms of heart rate, the vagus nerve helps to slow the heart rate by releasing neurotransmitters that activate muscarinic receptors in the heart, leading to decreased heart rate and reduced myocardial contractility. This action is often described as the 'rest and digest' response, counteracting the 'fight or flight' reactions of the sympathetic nervous system.

Regarding digestive functions, the vagus nerve stimulates the production of digestive enzymes and the secretion of gastric acid, enhancing the digestive process. It also promotes peristalsis, which is the wave-like muscle contractions that move food through the gastrointestinal tract.

The other nerves listed do not have these specific functions. The trochlear nerve is primarily involved in eye movement, the spinal accessory nerve mainly controls shoulder and neck muscles, and the hypoglossal nerve is responsible for tongue movements. Hence, the vagus nerve is uniquely positioned as the nerve that regulates heart rate and digestive processes.