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The muscles of respiration are those that contribute to inhalation and exhalation, aiding in the expansion and contraction of the thoracic cavity. The diaphragm is the major muscle responsible for breathing, and it is supported by a variety of other muscles. During inhalation, the diaphragm contracts, compressing the abdominal cavity and raising the ribs outward and upward, thereby expanding the thoracic cavity and drawing air into the lungs. The diaphragm is assisted by the intercostal muscles, which include the external and internal intercostals, as well as accessory muscles such as the sternocleidomastoid and scalenes. During exhalation, the diaphragm relaxes, and the elastic recoil of the lungs causes the thoracic cavity to contract, forcing air out of the lungs. Abdominal muscles, such as the rectus abdominis, external oblique, internal oblique, and transversus abdominis, are also involved in forceful exhalation. These muscles aid in breathing by contracting and raising abdominal pressure, pushing against the diaphragm, and reducing the volume of the thoracic cavity.
| Characteristics | Values |
|---|---|
| Primary inspiratory muscles | Diaphragm, external intercostals |
| Accessory inspiratory muscles | Sternocleidomastoid, scalenus anterior, medius, and posterior, pectoralis major and minor, serratus anterior, latissimus dorsi, serratus posterior superior, iliocostalis cervicis |
| Accessory expiratory muscles | Rectus abdominis, external oblique, internal oblique, transversus abdominis, iliocostalis, longissimus, serratus posterior inferior, quadratus lumborum |
| Muscles involved in inhalation | Diaphragm, intercostal muscles, neck muscles, abdominal muscles |
| Muscles involved in exhalation | Abdominal muscles, internal intercostal muscles |
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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 under the lungs and separates the abdominal cavity from the thoracic cavity. It is the primary muscle responsible for breathing, with the intercostal muscles playing a supporting role.
During inhalation, the diaphragm contracts and flattens, moving caudally (downward) and pulling the edges of the thoracic cavity upward and outward. This expansion of the thoracic cavity creates a vacuum, drawing air into the lungs. The diaphragm is also assisted by the sternocleidomastoid and scalene muscles on the neck, which elevate the sternum and clavicle, further lifting the ribs during inhalation.
Upon exhalation, the diaphragm relaxes and returns to its dome shape. This relaxation reduces the volume of the thoracic cavity, causing air to be forced out of the lungs. The abdominal wall muscles can also contract during forceful exhalation or when lung elasticity is reduced, pressing the abdominal organs upward into the diaphragm to aid in expelling air.
The diaphragm is a vital muscle for breathing, and any issues affecting its function can lead to breathing difficulties. Conditions such as multiple sclerosis (MS), ALS, spinal cord injuries, or lung issues like chronic obstructive pulmonary disease (COPD) can impact the diaphragm's ability to contract and relax properly, resulting in impaired breathing.
Breathing exercises, specifically diaphragmatic breathing exercises, can help strengthen the diaphragm and improve its efficiency. These exercises are beneficial for maintaining respiratory health and can also provide stress-relieving effects.
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Intercostal muscles aid breathing
Breathing is defined as pulmonary ventilation, which involves two events: inspiration, when air moves into the lungs, and expiration, when air leaves the lungs. The diaphragm and a variety of other muscles are involved in the process of ventilation. The diaphragm is the major 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, 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, drawing air into the lungs.
The intercostal muscles aid breathing by assisting in the expansion and contraction of the thoracic cavity. They have different layers that attach to the ribs to help build the chest wall. The internal intercostal muscles have fibres that are angled obliquely downward and backward from rib to rib. They also help in altering the anteroposterior dimension of the chest cavity. The external and internal intercostals do not work individually during breathing. They are assisted by the sternocleidomastoid and scalene muscles on the neck. The intercostal muscles are present in the trunk of the body and are essential for breathing.
The thoracic cage, which is a component of the thoracic wall, encloses the majority of the structures of the respiratory system. It forms the bony framework for breathing. The dome-shaped thoracic cage provides the necessary rigidity for organ protection, weight support for the upper limbs, and anchorage for muscles. The thoracic cage is composed of the thoracic skeleton, which includes the sternum, 12 pairs of ribs, and 12 thoracic vertebrae, associated with the costal cartilages and intervertebral discs, respectively. The ribs are lightweight and resilient, consisting of three types: true, false, and floating ribs. They form most of the thoracic cage, extending from the posterior to the anterior thoracic walls.
The intercostal muscles are susceptible to strain, which can be caused by a sudden increase in physical activity or overexertion during exercise. Intercostal muscle strain can cause sharp, direct pain, stiffness, and mobility difficulties. Treatment may involve cold and heat therapy, rest, and over-the-counter pain medications. In some cases, physical therapy, muscle relaxants, or injectable medications may be required. It is important to seek medical attention if breathing becomes difficult or painful.
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Abdominal muscles help with exhalation
The abdominal muscles are indeed involved in exhalation, alongside the diaphragm and intercostal muscles. The diaphragm is the major muscle responsible for breathing, and it is the primary inspiratory muscle, alongside the external intercostals.
During inhalation, the diaphragm contracts, moving its centre downwards and its edges upwards. This compresses the abdominal cavity, raising the ribs and expanding the thoracic cavity, which draws air into the lungs. When the diaphragm relaxes, the elastic recoil of the lungs causes the thoracic cavity to contract, forcing air out of the lungs.
The abdominal muscles come into play during forceful exhalation, or when the elasticity of the lungs is reduced, as in emphysema. The abdominal muscles contract, raising abdominal pressure and pushing the diaphragm against the lungs, which causes air to be pushed out. The abdominal muscles involved in exhalation are the rectus abdominis, external oblique, internal oblique, and transversus abdominis.
The abdominal muscles are also accessory expiratory muscles, which are recruited during exercise or when there is a dysfunction in the respiratory system. The accessory muscles are those that assist, but do not play a primary role, in breathing. During quiet breathing, there is little to no muscle contraction involved in exhalation, and it is driven by the elastic recoil of the lungs.
The abdominal muscles, therefore, play a crucial role in exhalation, particularly during periods of increased metabolic need, such as during exercise, or when the lungs' elasticity is reduced.
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Sternocleidomastoid and scalenes are accessory muscles
The process of breathing involves the movement of air between the atmosphere and the lung alveoli. This is known as pulmonary ventilation. The diaphragm and a variety of other muscles are involved in the process of ventilation. The diaphragm is the major 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, and during exhalation, it relaxes, allowing the elastic recoil of the lungs to force air out of the lungs.
The thoracic cage encloses the majority of the structures of the respiratory system. It forms a bony framework for breathing, offering protection and flexibility for ventilation. While the thoracic cage provides the necessary rigidity for organ protection, it would be impossible to breathe without the action of the thoracic muscles.
The sternocleidomastoid and scalenes are accessory muscles of respiration. Accessory muscles assist with breathing but do not play a primary role. They are typically recruited during times of exercise or during dysfunction in the respiratory system. The sternocleidomastoid and scalenes assist in elevating the rib cage. The scalenes are consistently physically active during quiet breathing, while the sternocleidomastoids are quiet. With an increase in respiratory volume, the sternocleidomastoids become active. Both muscles are simultaneously activated when one breathes in at the maximum flow rate.
The sternocleidomastoid muscle is one of the largest and most superficial cervical muscles. It originates at the manubrium of the sternum and the clavicle and has an insertion at the mastoid process of the temporal bone of the skull. It travels obliquely across the side of the neck and is thick and narrow at its centre, becoming broader and thinner at either end. The primary actions of the sternocleidomastoid muscle are rotation of the head to the opposite side and flexion of the neck.
The scalenes are three paired muscles of the lateral neck: the scalenus anterior, scalenus medius, and scalenus posterior. The scalenus medius is the largest and longest of the scalenes, while the scalenus posterior is the smallest and deepest. The main functions of the scalenes are flexion, lateral flexion, and rotation of the neck. They collectively act to elevate the first and second ribs, increasing the intrathoracic volume.
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Neck muscles help move the rib cage
The process of breathing involves two events: inspiration, when air moves into the lungs, and expiration, when air leaves the lungs. The diaphragm and a variety of other muscles are involved in the process of ventilation. The diaphragm is the major 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, so its centre moves caudally (downward) and 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. When the diaphragm relaxes, the elastic recoil of the lungs causes the thoracic cavity to contract, forcing air out of the lungs, and returning to its dome shape.
The intercostal muscles are also important in altering the anteroposterior dimension of the chest cavity. They consist of 11 pairs of muscles that run along the bodies and costal cartilages of the ribs between the sternum and the angle of the ribs. They attach between the costal groove and the superior border of two different ribs within the intercostal spaces. The external and internal intercostals do not work individually during breathing. They are assisted by the sternocleidomastoid and scalene muscles on the neck.
The sternocleidomastoid muscles originate from the manubrium of the sternum and sternal end of each clavicle. They insert on the mastoid process of the temporal bone and superior nuchal line of the occipital bone. This allows them to elevate the sternum and clavicle, subsequently lifting the ribs during inhalation. Therefore, they are used as accessory muscles in pulmonary ventilation. The scalenes are also accessory muscles that assist in elevating the rib cage. During quiet breathing, the scalenes are consistently physically active, while the sternocleidomastoids are quiet. With an increase in respiratory volume, sternocleidomastoids also become active. Both muscles are simultaneously activated when one breathes in at the maximal flow rate.
In conclusion, neck muscles such as the sternocleidomastoid and scalene muscles play a crucial role in aiding breathing by elevating the rib cage and assisting the intercostal muscles during inhalation.
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Frequently asked questions
The diaphragm is the major muscle responsible for breathing. It is a thin, dome-shaped muscle that separates the abdominal cavity from the chest cavity.
The intercostal muscles and neck muscles help move the rib cage and thus assist in breathing. The abdominal muscles are also involved in breathing out.
Accessory muscles of respiration are muscles that assist, but do not play a primary role, in breathing. These include the sternocleidomastoid and the scalenes (anterior, middle, and posterior).
During exercise, the expiratory muscles, including the abdominal muscles, play a more active role in breathing. The rib cage muscles contract during inspiration, while the abdominal muscles gradually relax, and vice versa during expiration.
