The phrenic nerve is he nerve that innervates the diaphragm. There are two phrenic nerves in the human body, left and right, and injury to either of them can cause serious health problems.
The diaphragm is a musculotendinous tissue that separates the thoracic cavity from the abdominal cavity and whose movement is responsible for the breathing.
To keep breathing steady, the phrenic nerve constantly transmits signals without the conscious control of the person, however, it is possible to exert some control over the diaphragm, which allows us, for example, to stop breathing in some situations.
Location of the phrenic nerves
Each phrenic nerve has its origin in the brain and from here they go down, each one on one side of the main cord of the spinal cord, encapsulated within the vertebral column.
At the level of the third, fourth, or fifth vertebrae, the phrenic nerves leave the spinal column.
The left phrenic nerve passes under the muscles of the neck and shoulder bones to the base of the left lung, where it contacts the heart and trachea. The right phrenic nerve follows a similar path, passing close to the heart before reaching the diaphragm.
the diaphragm
The diaphragm is a long, dome-shaped muscle located below the lungs. This muscle receives the signals for its movement through the phrenic nerves and is the responsible for breathing.
When a person inhales, the diaphragm contracts to give the lungs more room to fill with air. When a person exhales, the diaphragm relaxes and pushes the lungs up, helping waste gases from the body, such as carbon dioxide, to be expelled into the air.
Contraction/relaxation of the diaphragm also exerts pressure on the abdominal cavity helping to perform other bodily functions, such as urinating or vomiting.
It is one of the few muscles in the body that can function both voluntarily and involuntarily.
Involuntarily, the brain automatically sends commands to the diaphragm at a certain frequency to contract and relax without the person exercising any control. But the brain, voluntarily on the part of the person, can override or modify these automatic commands allowing the person to stop breathing if they need to for any reason.
But voluntary control has a limit, since the increasing accumulation of carbon dioxide in the blood stimulates the breathing center in the brain, which will send increasingly intense signals to the diaphragm until it exceeds voluntary signals. All this communication between the brain and the diaphragm to control breathing is done through the phrenic nerves.
Phrenic nerve functions
The main function of the phrenic nerves is transmission of brain commands to the diaphragm in both voluntary and involuntary control of breathing.
In addition, each phrenic nerve also collects sensory information that is transmitted to the brain.
Among this sensory information we can find information about whether the diaphragm is contracting properly, pain sensation and thermal sensation of the diaphragm and other organs of the thoracic cavity. With this sensory information the brain can regulate respiratory function properly and automatically.
Phrenic nerve injuries
Diseases that specifically affect the phrenic nerves are very common but usually come from systemic diseases (affecting the entire body or a large part). The main cause of injury to the phrenic nerves, however, is trauma to the neck, chest or abdomen, including surgical accidents.
Symptoms
The irritation of the phrenic nervess can lead to unusual symptoms. For example if can trigger the hiccup reflex, a sudden, involuntary, short contraction of the diaphragm that causes the lungs to take in a small amount of air. Another less common symptom of phrenic nerve involvement is pain at the tip of the scapula. This pain, known as Kehr's signit can be caused by very serious problems and should be evaluated by a health professional.
In general, shortness of breath is the main symptom that can alert to damage to the phrenic nerve if no other possible explanation is found. Because there are a pair of these nerves, a person can continue to breathe if only one has been damaged, but with difficulty. The phrenic nerve damage is considered a medical emergencyas the diaphragm can be completely paralyzed and the person may be unable to breathe, putting their life in danger.
Treatment
Most problems that affect the phrenic nerves and cause shortness of breath can resolve on their own over time because the nerves can regenerate themselves and make new connections. However, anyone who experiences breathing difficulties should see a doctor without fail so that the causes can be found out.
In cases of frequent breathing problems related to damage to the phrenic nerves, the patient may undergo surgery to implant a diaphragmatic pacemaker, a device that produces regular electrical shocks to contract the diaphragm. A surgical procedure is also sometimes used in which the diaphragm is modified to a lower position in order to give the lungs more room to expand.
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