Logan Steele
The muscles of respiration are the muscles that aid in inhalation and exhalation by helping to expand and contract the thoracic cavity. The diaphragm is the major muscle of respiration, but other muscles, including the intercostal muscles, abdominal muscles, and neck muscles, also play a role in the breathing process. The respiratory system is able to adjust breathing patterns based on changes in the internal and external environment, such as during exercise or in response to disturbances in the mechanics of breathing. The control of respiration involves both involuntary and voluntary mechanisms, with the medulla oblongata and pons in the brainstem playing key roles in regulating the rate and rhythm of breathing.
| Characteristics | Values |
|---|---|
| Muscles that control respiration | Diaphragm, intercostal muscles, abdominal muscles, laryngeal muscles, muscles in the oral and nasal pharynx, serratus anterior, pectoralis major and pectoralis minor, trapezius, latissimus dorsi, erector spinae, iliocostalis, quadratus lumborum, serratus posterior superior, serratus posterior inferior, levatores costarum, transversus thoracis, scalenes (anterior, middle, and posterior), sternocleidomastoid |
| Main function of the diaphragm | Separates the abdominal cavity from the thoracic cavity, contracts during inhalation, relaxes during exhalation |
| Main function of the intercostal muscles | Attached between the ribs, manipulate the width of the rib cage, assist in inhalation and exhalation |
| Main function of the abdominal muscles | Contract during exercise, push against the diaphragm, important during exhalation |
| Main function of the scalenes | Active during quiet breathing, assist in raising the rib cage |
| Main function of the sternocleidomastoid | Activated during increased respiratory volume, assist in raising the rib cage |
| Main function of the laryngeal muscles and muscles in the oral and nasal pharynx | Adjust the resistance of movement of gases during inspiration and expiration |
| Control of respiration | Voluntary and involuntary |
| Location of voluntary control | Primary motor cortex |
| Location of involuntary control | Respiratory centers of the upper brainstem (lower brain and cerebellum), medulla oblongata, pons |
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What You'll Learn
The diaphragm is the primary muscle for respiration
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, causing its centre to move downwards and its edges to move 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 returns to its original shape, forcing air out of the lungs.
The diaphragm is also involved in non-respiratory functions, such as expelling vomit, faeces, and urine from the body, and preventing acid reflux. Its function is supported by other muscle groups, including the intercostal muscles, which are attached between the ribs and help manipulate the width of the rib cage. The external intercostal muscles are most important in respiration, as their contraction raises each rib towards the rib above, elevating the rib cage and assisting in inhalation.
The intercostal muscles are also involved in exhalation, along with the abdominal muscles. During exhalation, the abdominal muscles contract, raising abdominal pressure and pushing against the lungs, forcing air out. While the diaphragm is the primary muscle for respiration, it is part of a complex arrangement of muscles that work together to facilitate the breathing process.
The muscles of respiration are also known as the 'breathing pump muscles'. They are composed of fatigue-resistant muscle fibres and are controlled by both voluntary and involuntary mechanisms. This means that we can choose to take a breath, but our bodies can also breathe automatically without conscious thought. The diaphragm is the most important of these muscles, and its function is carefully regulated by the nervous system and the brain.
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Intercostal muscles aid inhalation and exhalation
The intercostal muscles are one of the most important groups of respiratory muscles. They aid inhalation and exhalation by manipulating the width of the rib cage. During inhalation, the external intercostal muscles contract, raising each rib towards the rib above. This has the overall effect of raising the rib cage and assisting in inhalation.
The internal intercostal muscles have fibres that are angled obliquely downward and backward from rib to rib. These muscles assist in lowering the rib cage, adding force to exhalation.
There are three layers of intercostal muscles. The external intercostal muscles are most important in respiration. The contraction of these fibres raises each rib toward the rib above, with the overall effect of raising the rib cage, assisting in inhalation.
The intercostal muscles are attached between the ribs. They are controlled by both voluntary and involuntary mechanisms. During quiet breathing, the diaphragm is the predominant muscle of respiration. However, during exercise, many other muscles become important to respiration, including the intercostal muscles.
The intercostal muscles' elasticity is crucial to the health of the respiratory system and to maximise its functional capabilities.
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Accessory muscles assist breathing
Accessory muscles of respiration refer to muscles that provide assistance to the main breathing muscles, mainly when additional power is needed. They are also called the 'breathing pump muscles', forming a complex arrangement in the form of semi-rigid bellows around the lungs. All muscles attached to the human rib cage have the inherent potential to cause a breathing action.
The diaphragm and, to a lesser extent, the intercostal muscles drive respiration during quiet breathing. 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 thus expands the thoracic cavity. This expansion draws air into the lungs.
Accessory muscles are not active during regular breathing for a person in good health. However, they may use these muscles when taking a deliberately deep breath. For example, they can involve them when swimming underwater or forcefully expelling air to blow out birthday cake candles. The accessory muscles of inspiration lift the third, fourth, and fifth ribs to increase space for air in the lungs. The internal intercostal muscles have fibres that are angled obliquely downward and backward from rib to rib. The contraction of these fibres raises each rib toward the rib above, with the overall effect of raising the rib cage, assisting in inhalation.
The body may automatically activate the accessory muscles during typical breathing if someone has a condition that makes breathing more difficult. They are also recruited during exercise because of the increased metabolic need and during dysfunction in the respiratory system. Different life stages may also influence accessory muscle breathing. It is common to use the accessory muscle to help compensate for respiratory conditions leading to hypoxemia, a lower-than-typical level of oxygen in the blood, or hypercapnia, when the blood's carbon dioxide level rises above typical levels.
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The medulla oblongata controls respiration
The medulla oblongata is the primary control centre for respiration. Located in the brainstem, it is responsible for sending signals to the muscles that control breathing. The medulla oblongata contains chemoreceptors that detect the pH levels in the blood and spinal fluid, adjusting the ventilation rate to change acidity by increasing or decreasing the removal of carbon dioxide.
There are two regions in the medulla oblongata that control respiration: the ventral respiratory group and the dorsal respiratory group. The ventral respiratory group stimulates expiratory movements, while the dorsal respiratory group stimulates inspiratory movements. The medulla oblongata also controls reflexes for non-respiratory air movements, such as coughing and sneezing, swallowing, and vomiting.
The pons, located underneath the medulla oblongata, is another crucial structure in respiratory control. It works in conjunction with the medulla oblongata to regulate the ventilatory pattern of respiration. The pons control the rate or speed of involuntary respiration through its two main functional regions: the apneustic centre and the pneumotaxic centre. The apneustic centre sends signals for long and deep breaths, controlling the intensity of breathing. Meanwhile, the pneumotaxic centre acts to limit or inhibit the signals from the apneustic centre.
Together, the medulla oblongata and the pons form the respiratory centres of the brainstem, ensuring the proper functioning of the respiratory system by sending signals to the muscles involved in breathing and adjusting the ventilation rate as needed. The brainstem, including the medulla oblongata and the pons, plays a vital role in maintaining respiration and coordinating the complex interplay of muscles and reflexes involved in the breathing process.
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Voluntary and involuntary respiration
The muscles of respiration are also called the 'breathing pump muscles'. They form a complex arrangement in the form of a semi-rigid bellows around the lungs. All muscles attached to the human rib cage have the potential to cause a breathing action. The muscles that aid in expanding the thoracic cavity are called the inspiratory muscles, as they help in inhalation. Those that compress the thoracic cavity are called expiratory muscles, as they induce exhalation.
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 another important group of respiratory muscles. These muscles are attached between the ribs and manipulate the width of the rib cage. There are three layers of intercostal muscles, with the external intercostal muscles being most important in respiration. The contraction of these fibres raises each rib toward the rib above, with the overall effect of raising the rib cage, assisting in inhalation. The internal intercostal muscles have fibres that are angled obliquely downward and backward from rib to rib. These muscles can assist in lowering the rib cage, adding force to exhalation.
The accessory muscles are recruited during times of exercise or during dysfunction in the respiratory system. The sternocleidomastoid and the scalenes (anterior, middle, and posterior) are typically included, as they assist in elevating the rib cage. The involvement of these muscles depends on the degree of respiratory effort. 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.
Breathing is normally an unconscious, involuntary, and automatic process. The respiratory centre in the medulla and pons of the brainstem controls the rate and depth of respiration (the respiratory rhythm). However, humans are also able to voluntarily override automatic respiration, allowing breath-holding and prolonged vocalizations. The breathing muscles are controlled automatically from the brainstem during normal breathing but can also be controlled voluntarily from the motor cortex. The way these two drives to the breathing muscles interact is still not well understood.
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Frequently asked questions
The diaphragm is the primary muscle responsible for respiration. It is a thin, dome-shaped muscle that separates the abdominal cavity from the thoracic cavity.
The intercostal muscles, abdominal muscles, and neck muscles also play a role in respiration. The internal intercostal muscles have fibres that are angled obliquely downward and backward from rib to rib, while the external intercostal muscles are angled downward and forward. The contraction of these fibres raises or lowers the rib cage, aiding in inhalation or exhalation.
During inhalation, the diaphragm contracts, moving caudally (downward) and raising the ribs outward and upward, which expands the thoracic cavity and draws air into the lungs. During exhalation, the diaphragm relaxes, allowing the elastic recoil of the lungs to force air out.
Respiration is controlled by a combination of involuntary and voluntary mechanisms. The primary motor cortex in the brain is responsible for initiating voluntary muscular movements, including voluntary respiration. Involuntary respiration is controlled by the respiratory centres of the upper brainstem, which includes the medulla oblongata and the pons. The medulla sends signals to the muscles that initiate inspiration and expiration, while the pons controls the rate of involuntary respiration.
