The vagus nerve plays an essential role in the act of singing as well as in speaking. It has several tasks. Usually, nerves are either motor with direct command over muscles, or sensory if their task is to refer perceptual information. Some are both somatic motor and sensory. For instance, the fifth cranial nerve gives the face its sensitivity but also allows the mobility of the jaws.
The vagus nerve combines all of these functions. It is somatic, motor, sensory, and parasympathetic, giving it the ability to regulate the abdominal viscera. Moreover, it spreads over an immense area of the human body. Its contribution to phonation is fundamental. It is by design asymmetrical, with the right branch being shorter than the left. It emanates from the base of the skull, sends several sensory fibers to the dura mater covering of the brain, and then divides into various branches.
Let's begin with a closer look at the right vagus nerve. It is most important to remember that one of its branches innervates both the lower part of the external auditory canal and the tympanic membrane. This is its only external point of emergence but it plays an enormous role. It is also important to emphasize that the vagus nerve extends a sensory nerve fiber onto the muscle of the stirrup, which receives its motor activation from the facial nerve.
From The Ear and the Voice by Alfred A. Tomatis, Scarecrow Press, 2005.
"You will never get a bright tone with a dull face." —Harry Gregory Hast.