Question

The function of vagus nerve innervating the heart is to
A. Initiate the heartbeat
B. Reduce the heart beat
C. Accelerate the heart beat
D. Maintain constant heart beat

Answer 1

Hint: The vagus nerve runs from the brain through the face and thorax to the abdomen. It has the most extensive distribution of the cranial nerves.

Complete Answer:
- The vagus nerve is the tenth cranial nerve or CN X, and interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It is the longest nerve of the autonomic nervous system in the human body and consists of sensory and motor fibers.
- The sensory fibers originate from neurons of the nodose ganglion, whereas the motor fibers come from neurons of the dorsal motor nucleus of the vagus and the nucleus ambiguus.
- The vagus nerve has two sensory ganglia: the superior and the inferior ganglia. The sensory ganglia are masses of nerve tissue that transmit sensory impulses. The branches of the superior ganglion innervate the skin in the concha of the ear.
- The inferior ganglion gives off two branches: the pharyngeal nerve and the superior laryngeal nerve. The laryngeal nerve branches from the vagus into the lower neck and upper thorax to innervate the muscles of the larynx.
- The vagus also gives off cardiac, esophageal, and pulmonary branches. In the abdomen, the vagus innervates the greater part of the digestive tract and other abdominal viscera.

Sensory functions of the vagus nerve:
- Somatic sensation information for the skin behind the ear, the external part of the ear canal, and some parts of the throat.
- Visceral sensation information for the larynx, esophagus, lungs, trachea, heart, and most of the digestive tract.
- Also has a little role in providing a sensation of taste near the root of the tongue.

Motor functions of the vagus nerve:
- Stimulating muscles in the pharynx, larynx, and the soft palate.
- Stimulating muscles in the heart, where it acts to lower resting heart rate.
- Stimulating involuntary contractions in the digestive tract allowing food to move through the tract.

Hence, the vagus nerve which innervates the heart reduces the heartbeat. The correct option is B.

Note: Vagus nerve stimulation is sometimes used for patients with epilepsy or depression that is otherwise untreatable. In this, the nerve is stimulated with pulses of electricity.