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The diaphragm is the primary muscle responsible for breathing, and is supported by other muscles that aid in inhalation and exhalation. Located below the lungs, the diaphragm is a thin, dome-shaped muscle that contracts and flattens upon inhalation, creating a vacuum that pulls air into the lungs. During exhalation, the diaphragm relaxes and returns to its dome shape, forcing air out of the lungs. In addition to the diaphragm, various accessory muscles assist in respiration, including the sternocleidomastoid, scalenes, serratus anterior, pectoralis major, and pectoralis minor. These muscles help elevate the rib cage and facilitate breathing.
| Characteristics | Values |
|---|---|
| Major muscle of respiration | Diaphragm |
| Location | Below the lungs |
| Shape | Large, dome-shaped |
| Function | Contracts and flattens during inhalation, relaxes and returns to dome shape during exhalation |
| Other functions | Separates the chest cavity from the abdomen |
| Accessory inspiratory muscles | Sternocleidomastoid, scalenus anterior, medius, and posterior, pectoralis major and minor, serratus anterior and latissimus dorsi |
| Accessory expiratory muscles | Rectus abdominis, external oblique, internal oblique, and transversus abdominis |
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What You'll Learn
The diaphragm is the primary muscle for breathing
The diaphragm is a thin, dome-shaped muscle that sits below the lungs, separating the chest cavity from the abdomen. It is the primary muscle responsible for breathing, also known as respiration. During inhalation, the diaphragm contracts and flattens, moving downwards and increasing the length and diameter of the chest cavity. This expansion of the thoracic cavity creates a vacuum, drawing air into the lungs.
The diaphragm is attached to the sternum, the lower ribs, and the spine. Its contraction raises the ribs upward and outward, further enlarging the chest cavity. This process is known as inspiration, and the diaphragm is the major inspiratory muscle. The intercostal muscles, particularly the external intercostals, also play a role in inspiration by aiding in the expansion of the thoracic cavity. However, the diaphragm is the most crucial muscle for this process.
Upon exhalation, or expiration, the diaphragm relaxes and returns to its dome-like shape. This relaxation reduces the size of the thoracic cavity, causing air to be pushed out of the lungs. During quiet breathing, exhalation occurs passively due to the elastic recoil of the lungs and chest wall. However, during vigorous exercise or increased respiratory effort, the abdominal muscles become actively involved in exhalation.
The breathing cycle is controlled by the respiratory centre located in the brain stem, specifically the medulla oblongata and the pons. The diaphragm receives impulses from the dorsal respiratory group, which controls the initiation of breathing. When forced exhalation is required, the ventral respiratory group becomes active, sending impulses to the abdominal muscles and internal intercostals.
Several conditions and injuries can affect the diaphragm's function, leading to symptoms such as shortness of breath, chest pain, and difficulty swallowing. Diaphragmatic breathing exercises can help strengthen the diaphragm and improve its efficiency.
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Accessory muscles that aid breathing
The diaphragm is the primary muscle responsible for breathing. It is a thin, dome-shaped muscle that separates the abdominal cavity from the thoracic cavity. During inhalation, the diaphragm contracts, moving its centre downwards and its edges upwards. This compresses the abdominal cavity, raises the ribs and expands the thoracic cavity, drawing air into the lungs. When the diaphragm relaxes, the thoracic cavity contracts, and air is forced out of the lungs.
The intercostal muscles also play a role in breathing. The outer layer of intercostal muscles aids in normal breathing, while the inner layer assists with exhalation. The inner intercostal muscles are also accessory muscles of respiration.
Accessory muscles of respiration assist with breathing but do not play a primary role. They are typically used when breathing in and out forcefully, such as when blowing out a candle. They may also be used during normal breathing in people with disorders affecting their breathing, such as severe chronic obstructive pulmonary disease (COPD). Use of these muscles during rest may indicate respiratory distress or an underlying problem.
There is no definitive list of accessory muscles, but the following muscles have been observed contributing to respiration:
- Sternocleidomastoid
- Scalenus anterior
- Scalenus medius
- Scalenus posterior
- Serratus anterior
- Pectoralis major
- Pectoralis minor
- Trapezius
- Latissimus dorsi
- Erector spinae
- Iliocostalis
- Quadratus lumborum
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How intercostal muscles help breathing
The diaphragm is the primary muscle responsible for breathing. It is a thin, dome-shaped muscle located below the lungs, separating the abdominal cavity from the thoracic cavity. During inhalation, the diaphragm contracts and flattens, enlarging the chest cavity and creating a vacuum that pulls air into the lungs. Upon exhalation, the diaphragm relaxes, returning to its dome shape, and air is forced out of the lungs.
While the diaphragm is the main muscle of respiration, the intercostal muscles also play a crucial role in the breathing process. The intercostal muscles are divided into two groups: the external intercostals and the internal intercostals. The external intercostals are the primary inspiratory muscles that aid in inhalation. They lift and expand the rib cage, allowing air to enter the lungs. During deep inspiration, accessory chest wall muscles, such as the accessory inspiratory muscles, may also become involved.
The internal intercostals, on the other hand, assist in forceful exhalation. They pull down on the rib cage, helping to propel air out of the lungs. This is particularly important during physical activities or when increased respiratory effort is required. The internal intercostals are also essential for normal speech and singing, as they control the propulsion of air through the mouth and nose.
The intercostal muscles, along with the diaphragm, receive their blood supply from anterior and posterior intercostal arteries, as well as internal thoracic and musculophrenic arteries. The health and elasticity of these muscles are crucial to the respiratory system's optimal functioning.
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Abdominal muscles and breathing out
The diaphragm is the major muscle of respiration, located below the lungs. It is a thin, dome-shaped muscle that separates the abdominal cavity from the thoracic cavity. During inhalation, the diaphragm contracts and flattens, moving downward, while the chest cavity enlarges. This contraction creates a vacuum, pulling air into the lungs.
Upon exhalation, the diaphragm relaxes and returns to its dome shape, and air is forced out of the lungs. The abdominal muscles are accessory expiratory muscles that aid in exhalation by compressing the abdominal cavity and reducing the volume of the thoracic cavity. These muscles include the rectus abdominis, external oblique, internal oblique, and transversus abdominis.
To exhale using abdominal breathing, also known as diaphragmatic breathing, tighten your abdominal muscles and let your stomach fall inward while exhaling slowly through pursed lips. The chest should remain still during this process. This technique helps strengthen the diaphragm and improves lung efficiency. It is particularly beneficial for individuals with chronic obstructive pulmonary disease (COPD) as it can help retrain the body to engage the diaphragm, thereby alleviating symptoms such as shortness of breath.
Abdominal breathing exercises can be practised for 5 to 10 minutes, several times a day. To begin, place one hand on your upper chest and the other just below your rib cage. Breathe in slowly through your nose, allowing your stomach to move outward against your hand. Then, tighten your abdominal muscles and exhale slowly through pursed lips, letting your stomach move inward. With practice, diaphragmatic breathing will become more effortless, and you can gradually increase the duration and intensity of the exercises.
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Conditions that affect the diaphragm
The diaphragm is a muscle that plays a critical role in the respiratory system. When we breathe in, the diaphragm contracts and flattens, moving down towards the abdomen, creating a vacuum in the chest and allowing the lungs to expand and pull in air. Several conditions, diseases, and injuries can damage the diaphragm and affect its function.
One such condition is a diaphragmatic hernia, which can be congenital or acquired. Congenital diaphragmatic hernia (CDH) is a birth defect where a hole in the diaphragm allows the baby's digestive organs to move into the chest cavity, reducing space for the lungs and causing breathing problems. Acquired diaphragmatic hernia (ADH) can occur due to blunt trauma, stab wounds, or gunshot wounds, resulting in a hole in the diaphragm and the subsequent movement of digestive organs into the chest cavity, interfering with breathing. Hiatal hernia is another type of hernia where part of the stomach pushes through the diaphragm and into the oesophagus, causing acid reflux. Hernias may require surgical repair.
Phrenic nerve damage is another condition that can affect the diaphragm. This damage can result from cancer, autoimmune diseases, trauma, or surgery, such as heart bypass surgery and lung transplants. Additionally, nerve damage can be caused by a tumour, aortic aneurysm, or cervical spondylosis compressing or injuring the nerve. Conditions like HIV, Lyme disease, and West Nile virus can also lead to nerve inflammation.
Diaphragmatic paralysis refers to abnormal weakness and elevation of one or both hemidiaphragms, resulting in respiratory distress and potential respiratory failure. This paralysis can occur due to phrenic nerve injury or various factors such as surgical procedures, mechanical ventilation, metabolic disorders, inflammatory conditions, neuromuscular disorders, or mediastinal/abdominal masses causing lung hyperinflation.
Other conditions that can impact the diaphragm include diaphragmatic tumors, which are rare and often benign, and diaphragmatic endometriosis, observed in a small percentage of women of reproductive age with pelvic endometriosis.
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Frequently asked questions
The diaphragm is the major muscle of respiration. It is a thin, dome-shaped muscle that separates the abdominal cavity from the thoracic cavity.
During inhalation, the diaphragm contracts, moving down and increasing the length and diameter of the chest cavity, which expands the lungs. When the diaphragm relaxes, the lungs return to their resting shape and air is forced out.
Yes, the intercostal muscles and neck muscles help move the rib cage and assist in breathing. The abdominal muscles are also involved in breathing out, particularly during vigorous exercise.
Yes, the diaphragm can be strengthened through breathing exercises, which can also help reduce stress and improve overall health.
