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Vagus and phrenic nerves in the human body are the two crucial parts of the nervous system. In general, nerves act like cables that carry information (in the form of electrical impulses) from the brain to the rest of body parts. According to the functions, these nerves can be classified into three types- Sensory nerves, Motor nerves, and Mixed nerves.
- Vagus and Phrenic are examples of mixed nerves type.
- They do both motor (efferent) and sensory (afferent) functions in the human body.
- However, these both nerves have differences in their origin and function.
- Vagus nerve gives motion to digestive tract and phrenic nerve gives motion to diaphragm
- Sensory function of vagus nerve is in speech and taste whereas phrenic nerve senses the touch and pain.
| Table of Content |
Key terms: Nerves, Vagus nerve, Phrenic nerve, Cranial, Cervical nerves, Signals.
What is Vagus Nerve?
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Vagus nerves are also known as vagal nerves or cranial nerves X. They are the main nerves of the parasympathetic nervous system. These nerves control the involuntary functions of the body. For instance, breathing, heartbeat, and digestion are the functions that we can not control consciously. Vagus nerve is the 10th pair of the 12 cranial nerves and therefore it is called cranial nerves X.
- It carries signals from brain to heart and digestive tract.
- It is a key part of the parasympathetic nervous system.
- There are two vagal nerves- Right and Left.
- These both make up almost 75% of nerve fibers in the parasympathetic nervous system.
What Is Phrenic Nerve?
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The most important nerve among all the nerves in the body is the phrenic nerve. It has a significant role in respiration. It contracts and expands the diaphragm to make the lungs able to inhale and exhale air.
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Origin of Vagus and Phrenic Nerves
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Origins for vagus and phrenic nerves are different but both the nerves travel through the main organs and end to the site where they function.
Vagus nerve
The longest cranial nerves run from the brain to the large intestine. It originates in the medulla oblongata and passes through the neck, chest, lungs and digestive tract.
Phrenic nerve
Phrenic nerve connects to the C3 and C5 cervical nerve (neck region) roots of the spinal cord.
- It starts with C3 vertebral level.
- Connects to C4 and C5 level in neck.
- Travels through the neck, chest, heart and lungs to reach the diaphragm.
Function of Vagus and Phrenic Nerves
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Although, vagus and phrenic are both sensory and motor type of nerve, their role and site of functions are different.
Vagus Nerve Function
Vagus nerves play an important role in involuntary sensory and motor functions. Some of the major body responses where vagus nerve signals are listed below.
- Digestion
- Respiration
- Heart Rate and blood pressure
- Mood
- Immune system responses
- Skin/ muscle sensations
- Speech
- Urination
- Taste
Phrenic Nerve Function
Phrenic nerve controls diaphragm. It sends signals that cause the contraction and expansion of the diaphragm. Contraction of diaphragm will cause the lung to expand and inhale air. Expansion of diaphragm will lead to contraction of lungs so that it will exhale the carbon dioxide outside the body.
- Phrenic nerve is the only nerve that gives movement to the diaphragm (motor function).
- It also provides touch and pain sense (sensory function).
Differences Between Vagus and Phrenic Nerves
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Despite having both sensory and motor functions, vagus and phrenic nerves can be differentiated on the parameters like their types, origin and functions.
| Vagus nerve | Phrenic nerve |
|---|---|
| It is a cranial nerve | It is a cervical nerve |
| These nerves originate in the medulla oblongata. | It originates from the cervical plexus and connects between C3 to C5. |
| Vagus nerve gives signals between the brain, heart and digestive tract. Controls parasympathetic system | Phrenic nerve provides movement to the diaphragm. Controls respiration by contraction and expansion of diaphragm. Also gives touch and pain sensations. |
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Things to Remember
- Vagus nerves are the main nerves of the parasympathetic system.
- Vagal or vagus nerve is the 10th of 12 cranial nerves.
- It controls involuntary functions like digestion.
- It originates from medulla oblongata and passes through the neck, chest (thorax), heart and digestive tract.
- Phrenic nerve is the only nerve that gives movement to the diaphragm.
- It has a major function in respiration.
- Phrenic nerve originates from the cervical region and connects between C3 to C5.
- It travels through the neck, chest, lungs and reaches the diaphragm.
Sample Questions
Ques. What is the origin of vagus and phrenic nerves? (2 marks)
Ans. Vagus nerve: It originates in medulla oblongata and it passes through the neck, chest, lungs and last, to intestine. It is the tenth pair of cranial nerves.
Phrenic nerve: It originates from the neck region and connects the C3, C4 and C5. The nerves then pass through the neck, chest, lungs and end in diaphragm.
Ques. Why is the vagus nerve called cranial nerve X? (1 mark)
Ans. Vagus nerve is the tenth pair of cranial nerves hence it is known as cranial nerve X. Where X denotes the number 10.
Ques. What are the main body responses where the vagus nerve transmits the signals? (3 marks)
Ans. The major body responses in which the vagus nerve has an important role are listed below.
- Respiration
- Heart beat
- Digestion
- Mood
- Immune response
- Speech
- Taste
- Urine output
Ques. What are examples of involuntary function of the body? (2 marks)
Ans. Involuntary function means the function which is not under human control. For example, breathing, heartbeat and digestion are such functions of the body that we can not control consciously. However, such involuntary functions are under the control of the medulla oblongata which is a part of the brain and from where a vagus nerve originates.
Ques. What among the following is not the root of the vagus nerve? (1 mark)
(a) Neck-chest-lung-intestine
(b) Neck-chest-lung-diaphragm
(c) Neck-chest-lung-bladder
(d) Both b and c
Ans. d. Both b and c.
Explanation: Vagus nerve travels through the neck, chest, lungs and digestive tract. Neck-chest-lung-diaphragm is the root of the phrenic nerve and also the bladder is not involved in the root of the vagus nerve. So the answer is d.
Ques. Give difference between vagus nerve and phrenic nerve (4 marks)
Ans. Key differences between vagus and phrenic nerve are the type of nerve, origin and functions.
Type: Vagus nerve is a cranial nerve, while Phrenic nerve is cervical nerve.
Origin: Vagus nerve originates in medulla oblongata and phrenic nerve originates from cervical region.
Function: Vagus nerve has main function in transmitting the signal from brain to heart and intestine whereas phrenic nerve is involved in respiration, it contracts and expands the diaphragm for inhalation and exhalation of air.
Ques. How does a phrenic nerve regulate respiration? (3 marks)
Ans. Phrenic nerves give movement to the diaphragm. It causes the diaphragm to contract so the lung will expand and can take the air in (inhalation). Phrenic nerve will cause the diaphragm to expand when a lung needs to throw out the carbon dioxide. The expansion of the diaphragm will lead to contraction of the lung and it will exhale properly.
In other words, phrenic nerves send signals to the diaphragms and stimulate them to breathe. Damage in the spinal cord or brain will hinder this signaling and stimulation that eventually disturb the regulation of the respiration system.
Ques. What among the following is not a name of vagus nerve? (1 mark)
(a) Vagal nerve
(b) Cranial nerve X
(c) None of the above
(d) Parasympathetic fiber
Ans. d. Parasympathetic fiber.
Explanation: Parasympathetic fiber or nerve is the one part of the parasympathetic system. Vagal nerve and cranial nerve are the name for vagus nerve. Therefore the correct answer is option d.
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