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The muscles of respiration, also known as the 'breathing pump muscles', are the muscles that contribute to inhalation and exhalation by aiding in the expansion and contraction of the thoracic cavity. The diaphragm is the primary muscle responsible for respiration, with the intercostal muscles also playing a role. During inhalation, the diaphragm contracts and moves downward, increasing the volume of the thoracic cavity, which results in air being drawn in. When the diaphragm relaxes, the elastic recoil of the lungs causes the thoracic cavity to contract, forcing air out of the lungs. Accessory muscles, such as the sternocleidomastoid and the scalenes, may also assist in breathing during exercise or in cases of respiratory distress.
| Characteristics | Values |
|---|---|
| Main muscle responsible for breathing | Diaphragm |
| Diaphragm shape | Double-domed musculotendinous sheet |
| Diaphragm function | Contracts and moves downward, increasing the volume of the thoracic cavity and producing lung expansion |
| Diaphragm movement during normal breathing | 1.5 cm |
| Diaphragm movement during deep breathing | 7 cm |
| Secondary muscles responsible for breathing | Intercostal muscles |
| Accessory muscles | Sternocleidomastoid, scalene and serati anterior muscles |
| Abdominal muscles | Rectus abdominis, transverse abdominis, external oblique muscle and internal oblique muscle |
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What You'll Learn
The diaphragm is the main muscle for breathing
The diaphragm is the main muscle responsible for breathing. It is a thin, double-domed musculotendinous sheet of internal skeletal muscle that separates the abdominal cavity from the thoracic cavity. The diaphragm contracts and moves in an inferior direction, increasing the vertical diameter of the thoracic cavity and producing lung expansion, which draws air into the lungs.
During inhalation, the diaphragm contracts, and its centre moves caudally (downward), while its edges move cranially (upward). This compresses the abdominal cavity, raises the ribs upward and outward, and expands the thoracic cavity. This expansion draws air into the lungs. The diaphragm is also involved in the process of expiration, alongside the intercostal muscles. During normal expiration, the diaphragm relaxes, and the elastic recoil of the lungs and surface tension causes the thoracic cavity to contract, forcing air out of the lungs and returning to its dome shape.
The diaphragm is essential for respiration, and its contraction and relaxation alter the volume of the thoracic cavity and the lungs, producing inspiration and expiration. It is controlled by both voluntary and involuntary mechanisms, allowing for conscious control of breathing during speech, singing, or voluntary breath-holding. The diaphragm is also involved in deep breathing, where its movement can increase to facilitate greater lung capacity.
While the diaphragm is the primary muscle for breathing, other muscles also assist in the process. These include the intercostal muscles, which help move the rib cage, and the abdominal muscles, which are particularly important during vigorous exercise to facilitate exhalation. Accessory muscles, such as the sternocleidomastoid and scalenes, may also be recruited during deeper or more forceful breathing to further expand the thoracic cavity.
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Intercostal muscles aid breathing
Breathing is a complex process involving the coordinated movement of the chest wall, lungs, and the muscles that move them. The diaphragm, located directly below the lungs, is the main inspiratory muscle. During inspiration, it contracts and moves in an inferior direction, increasing the volume of the thoracic cavity and creating more room for the lungs to expand.
The intercostal muscles aid breathing by working with the diaphragm to facilitate inspiration and expiration. The intercostal muscles lie between the ribs and consist of three types: external intercostal muscles, internal intercostal muscles, and innermost intercostal muscles. When the intercostal muscles contract, the ribs move upward, and the rib cage expands, similarly expanding the thoracic cavity. This expansion increases the volume of the lungs, reducing the pressure. As pressure drops below atmospheric pressure, a pressure gradient is produced that moves air from the higher-pressure atmosphere into the lower-pressure lungs.
During expiration, the external intercostals, along with the diaphragm, relax. The intrathoracic volume decreases, intrapulmonary pressure increases, and air is expelled from the lungs. The internal intercostals are the major muscle group for exhalation, pulling down on the rib cage and pushing air out of the lungs. These muscles are essential for normal speech and singing, as they propel air out through the mouth and nose.
The intercostal muscles are also involved in forceful expiration, along with the abdominal muscles, subcostals, and intercostalis intimi. During vigorous exercise, the abdominal muscles are the most important, contracting to raise abdominal pressure and push a relaxed diaphragm against the lungs, causing air to be expelled.
In summary, the intercostal muscles aid breathing by working with the diaphragm to facilitate inspiration and expiration, with the external intercostals aiding inspiration and the internal intercostals aiding forceful expiration.
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Accessory muscles assist breathing
The muscles of respiration are also called the 'breathing pump muscles'. They form a complex arrangement in the form of semi-rigid bellows around the lungs. All muscles attached to the human rib cage have the potential to cause a breathing action. The diaphragm and the intercostal muscles are the muscles primarily responsible for respiration. The diaphragm is the main inspiratory muscle, and during inhalation, it contracts and moves in an inferior direction, increasing the vertical diameter of the thoracic cavity and producing lung expansion, which draws air in.
During normal breathing, the diaphragm may only move by 1.5 cm, but this can increase to 7 cm during deep breathing. The diaphragm is a double-domed structure with the muscular fibres blending into a central tendon. The surrounding muscular component is divided into three parts: sternal, costal, and lumbar. The diaphragm separates the thoracic and abdominal cavities and is the major muscle responsible for breathing. It is a thin, dome-shaped muscle. During inhalation, the diaphragm contracts, so its centre moves caudally (downward), and its edges move cranially (upward). This compresses the abdominal cavity, raises the ribs upward and outward, and thus expands the thoracic cavity. This expansion draws air into the lungs.
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Abdominal muscles help with exhalation
The abdominal muscles are a group of respiratory muscles that play a crucial role in exhalation, particularly during vigorous exercise. While inspiration is an active process, expiration is typically passive when the body is at rest. During inspiration, air enters the lungs, causing them to expand within the thoracic cavity. The diaphragm, the primary inspiratory muscle, contracts and moves downward, increasing the vertical diameter of the thoracic cavity. Simultaneously, the external intercostal muscles, which are also inspiratory muscles, elevate the rib cage, further expanding the thoracic cavity.
During normal, relaxed expiration, the inspiratory muscles relax. This relaxation, combined with the elastic recoil of the lungs and surface tension, allows the lungs and chest wall to return to their resting shape, expelling air from the lungs. The process of expiration is passive and does not require conscious effort when the body is at rest.
However, during vigorous exercise or other strenuous activities, expiration becomes an active process, and the abdominal muscles play a significant role in exhalation. The abdominal muscles contract, raising abdominal pressure, and pushing the diaphragm against the lungs, which facilitates the expulsion of air. This coordination between the abdominal muscles and the diaphragm prevents rib cage distortion and allows the diaphragm to act as a "'flow generator," optimising the mechanics of breathing during exercise.
The involvement of the abdominal muscles in exhalation is particularly evident during exercise or other forms of physical exertion. While the diaphragm primarily acts as a "flow generator" during exercise, the abdominal muscles function as "pressure generators." This means that they develop the pressure required to move the abdomen and facilitate exhalation. The activation of the abdominal muscles during exhalation helps decrease the volume of the abdomen below resting levels, reducing the end-expiratory lung volume during exercise.
In summary, the abdominal muscles are essential for exhalation, especially during periods of vigorous physical activity. While quiet and relaxed breathing relies primarily on the passive recoil of the lungs and chest wall, more forceful exhalation, such as during exercise, recruits the abdominal muscles to actively increase intra-abdominal pressure, aiding in the expulsion of air from the lungs.
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Neck muscles help move the rib cage
Breathing is defined as pulmonary ventilation, which is the movement of air between the atmosphere and the lung alveoli. The process of breathing involves two events: inspiration, when air moves into the lungs, and expiration, when air leaves the lungs. The lungs have no skeletal muscles of their own, and the work of breathing is done by the muscles attached to the rib cage.
The rib cage is a cage-like structure of bones that frames the chest cavity, also known as the thoracic cage. It consists of 37 bones and 98 joints, including 24 ribs (12 on each side) that wrap around the torso from front to back, connecting to the thoracic spine and the sternum (breastbone). The thoracic cage encloses the thoracic cavity, which contains the lungs, and forms the bony framework for breathing. The ribs are lightweight and flexible, allowing for the movement necessary for pulmonary ventilation.
The muscles attached to the rib cage that help with breathing are called the 'breathing pump muscles'. They form a complex arrangement around the lungs, and their contraction and relaxation alter the volume of the thoracic cavity and the lungs, producing inspiration and expiration. The diaphragm is the main inspiratory muscle, and during inspiration, it contracts and moves downwards, increasing the vertical diameter of the thoracic cavity and producing lung expansion, which draws air in. The diaphragm also plays a role in expiration, a passive process that occurs due to the elastic recoil of the lungs and muscles.
The intercostal muscles, including the external, internal, and innermost layers, also play a crucial role in breathing. These muscles fill the spaces between the ribs and assist in expanding the chest wall during inhalation and collapsing the lungs during exhalation. Additionally, the contraction of the intercostal muscles lifts the rib cage up and out, increasing the anteroposterior diameter of the thoracic cavity and aiding breathing.
Neck muscles, along with intercostal muscles, help move the rib cage and assist in breathing. The rib cage provides attachments for extrinsic skeletal muscles of the neck, upper limbs, upper abdomen, and back. These neck muscles contribute to the movement of the rib cage during the breathing process, working in conjunction with the diaphragm and intercostal muscles to facilitate inhalation and exhalation.
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Frequently asked questions
The diaphragm is the main muscle that produces normal breathing. It is a thin, dome-shaped muscle that separates the abdominal cavity from the thoracic cavity. During inhalation, the diaphragm contracts, so its centre moves caudally (downward) and its edges move cranially (upward). This compresses the abdominal cavity, raises the ribs, and expands the thoracic cavity, drawing air into the lungs.
The intercostal muscles and neck muscles help move the rib cage and assist in breathing. The internal intercostal muscles have fibres that are angled obliquely downward and backward from rib to rib. The external intercostals are also considered primary muscles of inspiration.
Accessory muscles are muscles that assist in breathing but do not play a primary role. They are used during forced inspiration or when breathing more deeply and forcefully, such as during exercise. Accessory muscles include the sternocleidomastoid, scalene, serratus anterior, pectoralis major, and pectoralis minor.
