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The muscles of respiration are the mechanical effectors of the breathing system. They are divided into three groups: inspiratory muscles, expiratory muscles, and accessory muscles of respiration. The diaphragm, a dome-shaped muscle separating the chest and abdominal cavities, is the primary muscle for inspiration, contracting to expand the chest cavity and lungs. Intercostal and neck muscles also assist in inspiration by elevating the rib cage. During quiet breathing, exhalation is passive, driven by lung elasticity, but abdominal muscles, including the rectus abdominis, external oblique, and internal oblique, are recruited during exercise or forceful exhalation.
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What You'll Learn
The diaphragm is the major muscle of inspiration
The diaphragm is a dome-shaped muscle that separates the chest cavity from the abdomen. It is attached to the base of the sternum, the lower parts of the rib cage, and the spine. When the diaphragm contracts, it increases the length and diameter of the chest cavity, expanding the lungs and facilitating inhalation. This process is known as inspiration.
The diaphragm is the primary muscle responsible for inspiration, and its function is essential for breathing. During inspiration, the diaphragm contracts and moves inferiorly, creating a vacuum effect within the chest cavity. This vacuum leads to a drop in pleural pressure (Ppl) and a simultaneous rise in abdominal pressure (Pab). As a result, the ventral abdominal wall expands, and the rib cage contracts, allowing air to be pulled into the lungs.
The diaphragm's ability to generate pressure is enhanced during inspiration. The contraction of the diaphragm muscles causes the dome-shaped structure to descend, further increasing the volume of the chest cavity. This mechanical advantage provided by the diaphragm's shape and position is crucial for effective inspiration.
In addition to the diaphragm, other muscles also assist in the process of inspiration. These include the intercostal muscles, which are located between the ribs, and the neck muscles. The intercostal muscles, particularly the external intercostals, contribute to the expansion of the rib cage during inspiration. The neck muscles help move the rib cage, facilitating the inhalation of air.
During vigorous exercise, the demand for oxygen increases, and various muscles become involved in the process of inspiration. The abdominal muscles, for example, contract to raise abdominal pressure and push against the diaphragm, aiding in the inhalation process. This additional muscular support during exercise ensures that the body receives an adequate supply of oxygen to meet the increased metabolic needs of physical activity.
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Abdominal muscles are the most important for exhalation
The abdominal muscles are indeed the most important for exhalation. While the diaphragm is the primary muscle of inhalation, the abdominal muscles are the most important for exhalation, especially during vigorous exercise.
The diaphragm is a dome-shaped muscle that separates the chest cavity from the abdomen. When it contracts, it increases the length and diameter of the chest cavity, expanding the lungs. The intercostal and neck muscles also help move the rib cage and assist in inhalation.
During exhalation, the diaphragm and external intercostals relax. The intrathoracic volume decreases, intrapulmonary pressure increases, and air is expelled from the lungs. The abdominal muscles, including the rectus abdominis, external oblique, internal oblique, and transversus abdominis, contract and raise abdominal pressure. This pushes the relaxed diaphragm against the lungs, causing air to be pushed out.
The abdominal muscles are also important for stabilizing the body during motion. They help optimize the action of the muscles that contribute to both breathing and locomotion, allowing for body stabilization during movement.
It is worth noting that during normal, quiet breathing, exhalation is a passive process. The elasticity of the lungs and chest wall, which are stretched during inhalation, causes them to return to their resting shape and expel air when the inspiratory muscles relax. However, during vigorous exercise or other activities that require forced exhalation, such as playing an instrument, the abdominal muscles become crucial for active exhalation.
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The intercostal muscles drive respiration during quiet breathing
The intercostal muscles are a group of respiratory muscles that act on the chest wall and its compartments. They are the muscles that fill the spaces between the ribs and are essential for breathing, as they help move the rib cage and assist in inhalation and exhalation.
During quiet breathing, the diaphragm contracts and pulls the lower surfaces of the lungs downwards, increasing the length and diameter of the chest cavity and expanding the lungs. The intercostal muscles work simultaneously with the diaphragm, lifting the ribs and pushing the abdominal organs down, thereby increasing the intrathoracic volume. The diaphragm is a dome-shaped muscle that separates the chest cavity from the abdomen and is the primary muscle used for inhalation.
The intercostal muscles are divided into two groups: the external intercostals and the internal intercostals. The external intercostals are the muscles of inspiration, as they elevate the rib cage and assist the diaphragm in expanding the lungs. The internal intercostals are accessory expiratory muscles, acting on the abdomen and abdominal rib cage to induce exhalation.
The breathing cycle is controlled by the respiratory centre located inside the medulla oblongata and the pons of the brain stem. The dorsal respiratory group within the dorsal portion of the medulla is responsible for the largest part of the breathing cycle, sending impulses through the phrenic nerve to the diaphragm and through the intercostal nerves to the external intercostal muscles. When the dorsal respiratory group stops firing impulses, the muscles relax, and exhalation occurs.
In summary, the intercostal muscles, particularly the external intercostals, play a crucial role in quiet breathing by working in conjunction with the diaphragm to elevate the rib cage and expand the lungs.
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The accessory muscles of respiration assist breathing
The accessory muscles of respiration refer to muscles that provide assistance to the main breathing muscles. They are recruited during exercise or in cases of respiratory dysfunction, when additional power is needed.
The primary inspiratory muscles are the diaphragm and external intercostals. The diaphragm is the most important muscle used for breathing in. As the diaphragm contracts, it increases the length and diameter of the chest cavity, expanding the lungs. The intercostal muscles and neck muscles help move the rib cage and assist in breathing.
The accessory inspiratory muscles include the sternocleidomastoid, the scalenus anterior, medius, and posterior, the pectoralis major and minor, the serratus anterior and latissimus dorsi, and the serratus posterior superior. The sternocleidomastoid muscles elevate the sternum and clavicle, lifting the ribs during inhalation. The scalenus anterior, medius, and posterior muscles also play a role in inspiration.
The abdominal muscles are the most important expiratory muscles. They contract, raise abdominal pressure, and push a relaxed diaphragm against the lungs, causing air to be pushed out. The internal intercostals, intercostalis intimi, subcostals, and the lowest fibres of the iliocostalis and longissimus, the serratus posterior inferior, and quadratus lumborum also help in forceful expiration.
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The muscles of the upper airway are also considered muscles of respiration
The respiratory system is made up of the organs and structures in the body that enable breathing. This includes the lungs, nose, mouth, and the tubelike structures (airways) that connect them. The airways are subdivided into the conducting zone and the respiratory zone. The conducting airways carry air in and out of the lungs, while the respiratory zone, formed by alveoli, is the site of gas exchange. The upper respiratory tract brings air into the body and helps move it toward the lungs.
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 that are attached to the human rib cage have the inherent potential to cause a breathing action. Muscles that help expand the thoracic cavity are called the inspiratory muscles because they aid in inhalation. Those that compress the thoracic cavity are called expiratory muscles, which induce exhalation.
The accessory inspiratory muscles include the sternocleidomastoid, the scalenus anterior, medius, and posterior, the pectoralis major and minor, the inferior fibres of serratus anterior and latissimus dorsi, and the serratus posterior superior, which may help in inspiration. Technically, any muscle attached to the upper limb and the thoracic cage can act as an accessory muscle of inspiration through reverse muscle action. The accessory expiratory muscles are the abdominal muscles: rectus abdominis, external oblique, internal oblique, and transversus abdominis. The accessory muscles are recruited during times of exercising because of the increased metabolic need and also during dysfunction in the respiratory system.
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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 chest cavity from the abdomen.
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).
The diaphragm contracts, increasing the length and diameter of the chest cavity, and thus expanding the lungs. The intercostal muscles and neck muscles help move the rib cage, further assisting in the breathing process.
