Difference Between Vagus and Phrenic Nerves

The key difference between vagus and phrenic nerves is that vagus nerve is the tenth cranial nerve, which is an important parasympathetic cranial nerve, while phrenic nerve is a nerve of the thoracic region and is important for breathing.

Vagus nerve is the tenth cranial nerve. It is the longest and most complex of the cranial nerves. It provides the parasympathetic supply for all the organs of the thorax and abdomen. Phrenic nerve is the motor and sensory nerve of the diaphragm. Both vagus and phrenic nerves are thoracic nerves. They are mixed nerves. Vagus and phrenic nerves have both motor and sensory divisions. There are right and left vagus and phrenic nerves.

CONTENTS

1. Overview and Key Difference
2. What are Vagus Nerves
3. What are Phrenic Nerves
4. Similarities Between Vagus and Phrenic Nerves
5. Side by Side Comparison – Vagus vs Phrenic Nerves in Tabular Form
6. Summary

What are Vagus Nerves?

Vagus nerve is the tenth cranial nerve that extends from the head, the neck, the thorax, and the abdomen. It is the longest of the 12 cranial nerves.  It originates in the medulla oblongata. Structurally, vagus nerves are mixed nerves. They possess somatic and visceral afferent fibres, as well as general and special visceral efferent fibres.

Vagus nerves mediate oesophagal swallowing, gastric emptying and meal satiety. Therefore, vagus nerves interfere with parasympathetic control of the heart, lungs, and digestive tract. Vagus nerve is responsible for the heart rate, gastrointestinal peristalsis, sweating, and quite a few muscle movements in the mouth, including speech. There are right and left vagus nerves.

What are Phrenic Nerves?

Phrenic nerve is a nerve of the thorax region. It is the nerve that provides motor innervation to the diaphragm. The diaphragm is the main muscle of respiration. Hence, the phrenic nerve plays a crucial role in breathing.

Phrenic nerve is a bilateral mixed nerve, which is the motor and sensory nerve. It originates from the cervical spinal roots C3, C4 and C5 in the neck. It descends through the thorax to diaphragm. There are two phrenic nerves: right phrenic nerve and left phrenic nerve. Both phrenic nerves innervate the inferior surface of the diaphragm. Phrenic nerves possess efferent and afferent fibres.

What are the Similarities Between Vagus and Phrenic Nerves?

• Vagus and phrenic nerves start in the neck and run downward in the mediastinum and pass through the diaphragm.
• There are right and left phrenic nerves and right and left vagus nerves.
• Both vagus and phrenic nerves are mixed nerves.

What is the Difference Between Vagus and Phrenic Nerves?

Vagus nerve, which is the tenth cranial nerve, is an important parasympathetic cranial nerve while the phrenic nerve is the mixed nerve that provides the innervation to the diaphragm. So, this is the key difference between vagus and phrenic nerves. Also, vagus nerves originate from the medulla oblongata while phrenic nerves originate from the cervical plexus and receive innervation from the C3, C4, and C5 nerve roots.

Moreover, another difference between vagus and phrenic nerves is their function. Vagus nerves mediate the parasympathetic control of the heart, lungs, and digestive tract, while the phrenic nerves supply motor fibres to the diaphragm and sensory fibres to the fibrous pericardium, mediastinal pleura, and diaphragmatic peritoneum.

Below infographic summarizes the differences between vagus and phrenic nerves in tabular form.

Summary – Vagus vs Phrenic Nerves

Vagus nerves and phrenic nerves are thoracic nerves. They both run bilaterally down the neck and thorax. Vagus nerve is an important parasympathetic cranial nerve. Phrenic nerve is a motor nerve that provides motor innervations to the diaphragm and sensory innervation to the central intrathoracic and peritoneal surfaces of the diaphragm. Both vagus and phrenic nerves are mixed nerves that contain both motor and sensory divisions. Thus, this summarizes the difference between vagus and phrenic nerves.

Reference:

1. “Phrenic Nerve.” Physiopedia, Available here.
2. “Vagus Nerve.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 13 Mar. 2020, Available here.

Image Courtesy:

1. “Gray793” By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body. Bartleby.com: Gray's Anatomy, Plate 793 (Public Domain) via Commons Wikimedia
2. “Gray806” By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body. Bartleby.com: Gray's Anatomy, Plate 806 (Public Domain) via Commons Wikimedia