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The diaphragm is the major muscle responsible for breathing. It is a dome-shaped muscle that separates the chest cavity from the abdominal cavity. During inhalation, the diaphragm contracts, moving down and increasing the length and diameter of the chest cavity, which expands the lungs. The intercostal muscles and neck muscles help move the rib cage and assist in breathing. The abdominal muscles are also involved in breathing out, especially during vigorous exercise. The elasticity of these muscles is crucial to the health of the respiratory system.
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What You'll Learn
The diaphragm muscle
The diaphragm is a dome-shaped muscle located below the lungs, separating the chest cavity from the abdominal cavity. It is the primary muscle responsible for breathing, also known as inhalation or inspiration. During inhalation, the diaphragm contracts and flattens, moving downwards and increasing the length and diameter of the chest cavity. This expansion of the chest cavity creates a slight vacuum, drawing air into the lungs.
The diaphragm is attached to the base of the sternum, the lower parts of the rib cage, and the spine. Its contraction raises the ribs upward and outward, further expanding the thoracic cavity and facilitating inhalation. The intercostal muscles, which are attached between the ribs, also play a crucial role in respiration by manipulating the width of the rib cage. The external intercostal muscles, in particular, aid in inhalation by raising each rib toward the rib above, resulting in the elevation of the rib cage.
During exhalation, or expiration, the diaphragm relaxes and returns to its dome-like shape. This relaxation causes the elastic recoil of the lungs, resulting in the contraction of the thoracic cavity and the expulsion of air from the lungs. While exhalation is typically a passive process driven by the lungs' elasticity, the abdominal muscles become involved during vigorous exercise or forceful exhalation. The abdominal muscles contract, raise abdominal pressure, and push against a relaxed diaphragm, facilitating the exhalation of air.
The diaphragm is composed of fatigue-resistant muscle fibres and is controlled by both voluntary and involuntary mechanisms. Its rhythmic and continual contractions occur involuntarily most of the time, ensuring that breathing happens automatically, even during sleep or unconsciousness. However, individuals can also voluntarily control their breathing during speech, singing, or voluntary breath-holding.
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Intercostal muscles
There are three layers of intercostal muscles: external, internal, and innermost. These muscles combine to fill the space between the ribs and support the rib cage. The external intercostals are the outermost layer, originating from the lower border of the rib above and inserting into the upper border of the rib below. They are responsible for elevating the ribs and expanding the chest wall during inhalation. The internal intercostals are the intermediate layer, originating from the costal groove of one rib and inserting into the superior border of the rib below. They help collapse the lung during exhalation by depressing the ribs and bending them inward. The innermost intercostals are the deepest layer, originating from the costal groove of one rib and inserting into the superior border of the rib below. They assist the internal and external intercostals in their function.
All three layers of intercostal muscles are accessory respiratory muscles that participate in the process of forced breathing. The external intercostals facilitate forced inspiration, while the internal and innermost intercostals aid in forced expiration. The intercostal muscles are innervated by the intercostal nerves and receive their blood supply from the intercostal arteries.
Intercostal muscle strains can occur due to overexertion, direct trauma, or repetitive torso twisting. Symptoms of a strain include pain, muscle tension and stiffness, and shallow breathing patterns to avoid pain.
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Abdominal muscles
The abdominal muscles are one of the three groups of respiratory muscles, the other two being the diaphragm and rib cage muscles. The abdominal muscles are expiratory, which means they aid in exhalation. During inspiration, the abdominal muscles relax, and during expiration, they contract.
Breathing exercises such as diaphragmatic breathing can help improve breathing control. To perform diaphragmatic breathing, lie on your back on a flat surface with your knees bent. Place one hand on your upper chest and the other on your belly, just below your rib cage. Breathe in slowly through your nose, letting the air in deeply towards your lower belly. Tighten your abdominal muscles and let them fall inward as you exhale through pursed lips.
Diaphragmatic breathing can also help generate intra-abdominal pressure for posture control and accomplish slow respiration. It can be beneficial for people with asthma or chronic obstructive pulmonary disease (COPD) by improving their breathing during strenuous activities.
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Accessory muscles
The diaphragm is the main muscle used for breathing. However, during strenuous exercise, the diaphragm can become overloaded, and accessory muscles are used to assist with breathing. In healthy individuals, accessory muscles are not active during regular breathing. However, they may be used when taking a deep breath, such as when swimming underwater or blowing out birthday candles.
The accessory inspiratory muscles include the sternocleidomastoid, the scalenus anterior, medius, and posterior, the pectoralis major and minor, the inferior fibres of the serratus anterior and latissimus dorsi, and the serratus posterior superior. These muscles help to elevate the ribs and sternum, increasing the space for air in the lungs.
The accessory muscles of respiration undergo contraction and relaxation, altering the volume of the thoracic cavity and the lungs, thus producing inspiration and expiration.
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Muscles of the face, mouth and pharynx
The muscles of the face, mouth, and pharynx play a crucial role in controlling the lips, tongue, soft palate, and other structures to facilitate breathing. These muscles are an integral part of the musculoskeletal system and are responsible for various functions, including facial expressions and chewing.
The face contains about 20 flat skeletal muscles that extend from the scalp to the neck and are positioned around openings such as the mouth, eyes, nose, and ears. These muscles work together to enable movements like smiling, frowning, and raising eyebrows. They originate from bones or fibrous structures of the skull and connect to the skin, allowing for facial expressions.
The mouth, or buccolabial group of muscles, consists of 11 muscles that control the shape and movements of the mouth and lips. These include muscles for elevating and depressing the upper and lower lips, such as the levator labii superioris, risorius, and depressor labii inferioris. The orbicularis oris is a circular muscle that surrounds the mouth and forms the majority of the lips, enabling functions like whistling, singing, and vocal emphasis.
The oral muscles of facial expression are a subset of the facial muscles and include the orbicularis oris, buccinator, and various smaller muscles. These oral muscles are responsible for movements of the mouth and lips, adding emphasis to vocal communication. The orbicularis oris, also known as the main sphincter muscle of the lips, closes the lips and narrows the oral opening.
The nasal muscles, another group of facial muscles, are associated with movements of the nose and the surrounding skin. The procerus muscle, located between the eyebrows, helps pull them downward and flare the nostrils. The nasal muscles also contribute to breathing by regulating airflow through the nostrils.
In summary, the muscles of the face, mouth, and pharynx have diverse functions related to breathing, facial expressions, and oral movements. Their coordinated contractions and relaxations enable us to breathe, communicate, and express a range of emotions through facial gestures.
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Frequently asked questions
The diaphragm is the main muscle used for breathing. It is a dome-shaped muscle that separates the chest cavity from the abdominal cavity.
During inhalation, the diaphragm contracts and flattens, moving down and increasing the length and diameter of the chest cavity, which expands the lungs. This creates a vacuum, pulling air into the lungs.
When exhaling, the diaphragm relaxes and returns to its dome shape, forcing air out of the lungs.
Yes, the intercostal muscles and neck muscles help move the rib cage and assist in breathing. The abdominal muscles are also involved, especially during vigorous exercise.
