Dominic Stone
Accessory muscles are not used during normal breathing and are defined as the contraction of any muscle other than the diaphragm during inspiration or the contraction of any muscle during expiration. They are found around the shoulders, neck and upper chest and are usually activated when a person tries to take in a big breath or forcefully breathe out. Accessory muscles of inspiration include the scalene, sternocleidomastoid, trapezius and pectoralis major muscles, while the abdominal wall muscles are the main accessory muscles of expiration.
| Characteristics | Values |
|---|---|
| Definition | Accessory muscle use is defined as the contraction of any muscle other than the diaphragm during inspiration or the use of any muscle during expiration. |
| Location | Found around the shoulders, neck, and upper chest. |
| Function | Accessory muscles are recruited during exercise or during dysfunction in the respiratory system. They assist in inhalation and exhalation by aiding in the expansion and contraction of the thoracic cavity. |
| Activation | Accessory muscles are automatically activated when a person is not taking in enough oxygen or is unable to breathe out enough air. |
| Types | Accessory muscles of inspiration include the scalene, sternocleidomastoid, trapezius, and pectoralis major muscles. Accessory muscles of expiration include the abdominal wall muscles. |
| Blood Supply | The phrenic nerve provides motor nerve supply, and the phrenic nerve and intercostal nerve provide sensory supply. The inferior phrenic arteries deliver the majority of the blood supply. |
| Treatment | Accessory muscle use is often a sign of an underlying respiratory problem. Treatment should focus on addressing the underlying cause to reduce accessory muscle use. |
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What You'll Learn
- Accessory muscles are recruited during exercise or respiratory dysfunction
- They are inspiratory or expiratory muscles
- Accessory muscles of inspiration include the scalene, sternocleidomastoid, trapezius and pectoralis major muscles
- Accessory muscles of expiration include the abdominal wall muscles
- Use of accessory muscles during normal breathing indicates an underlying problem
Accessory muscles are recruited during exercise or respiratory dysfunction
Accessory muscles are not primarily responsible for respiration but can assist in breathing when there is an increased demand for oxygen, such as during exercise, or when the primary muscles of respiration are not sufficient to achieve adequate gas exchange. The primary muscles involved in breathing are the diaphragm and the intercostal muscles, which are responsible for most air movement in and out of the lungs during quiet, relaxed breathing.
During exercise, the body's demand for oxygen increases, leading to the recruitment of accessory muscles. These muscles provide assistance to the main breathing muscles when additional power is needed. The accessory inspiratory muscles include the sternocleidomastoid, which helps lift the sternum and allows for greater expansion of the lungs, and the scalenus anterior, medius, and posterior, which help lift the first two ribs and contribute to the anteroposterior expansion of the chest.
The accessory expiratory muscles are the abdominal muscles: rectus abdominis, external oblique, internal oblique, and transversus abdominis. These muscles work to depress the ribs and sternum during exhalation. The accessory muscles of the anterior thoracic wall include the sternalis muscle, variations of pectoralis major such as pectoralis minimus, and the axillary arch (Langer's).
Accessory muscles are also recruited during respiratory dysfunction, such as in cases of airway pathologies like COPD or asthma, where breathing becomes difficult or laborious. They can be crucial for breathing support during medical conditions, and their use generally warrants prompt medical evaluation and intervention.
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They are inspiratory or expiratory muscles
Accessory muscles are those that provide assistance to the main breathing muscles, primarily when additional power is needed, such as during exercise or in cases of airway pathologies (e.g. COPD). They are inspiratory or expiratory muscles, aiding in inhalation or exhalation, respectively.
The inspiratory muscles are those that help to expand the thoracic cavity, increasing the vertical diameter and producing lung expansion, which in turn draws air into the lungs. The diaphragm is the main inspiratory muscle, with the external intercostal muscles, internal intercostal muscles, and innermost intercostal muscles also contributing. Accessory inspiratory muscles include the sternocleidomastoid, scalenus anterior, medius, and posterior, pectoralis major and minor, and serratus anterior, among others. These muscles elevate the ribs and sternum during inhalation.
The expiratory muscles, on the other hand, compress the thoracic cavity, inducing exhalation. The abdominal muscles, including the rectus abdominis, external oblique, internal oblique, and transversus abdominis, are accessory expiratory muscles. In addition, muscles in the thoracolumbar region, such as the lowest fibres of iliocostalis and longissimus, also aid in exhalation. These muscles depress the ribs and sternum.
During normal, quiet breathing, inspiration is an active process due to the contraction of the diaphragm and other inspiratory muscles, while expiration is passive, resulting from the elastic recoil of the lungs and surface tension. However, during exercise or other periods of increased metabolic need, accessory muscles are recruited to aid in breathing, increasing the size of the thoracic cavity and enhancing ventilation.
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Accessory muscles of inspiration include the scalene, sternocleidomastoid, trapezius and pectoralis major muscles
Accessory muscles, also known as accessory muscles of inspiration, are those that are not used during normal breathing. They are only activated when a person with healthy lungs takes a large breath or when an individual with a breathing disorder inhales or exhales. Accessory muscles of inspiration include the scalene, sternocleidomastoid, trapezius, and pectoralis major muscles. These muscles are located around the neck, shoulders, and upper chest.
The scalene muscles, which include the scalenus anterior, medius, and posterior, are often activated during inspiration in patients with severe obstructive disease. The contraction of these muscles, along with the sternocleidomastoid muscles, lifts the clavicles and first ribs, expanding the thorax. This helps to increase the volume of the thoracic cavity and the lungs, making it easier for air to enter.
The sternocleidomastoid and scalene muscles are the most commonly used accessory muscles during inspiration. They are also known as the breathing pump muscles, forming a complex arrangement around the lungs. The trapezius muscle is also an accessory muscle of inspiration and is located in the upper back, extending to the neck and shoulders.
The pectoralis major muscle is a large, fan-shaped muscle that connects the chest wall to the upper arm. It is also considered an accessory muscle of inspiration. During inspiration, the contraction of the pectoralis major, along with the other accessory muscles, lifts the breastbone, upper ribs, and collarbones. This movement elevates the ribs and sternum, causing the upper chest to rise and creating more space in the lungs for air to enter.
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Accessory muscles of expiration include the abdominal wall muscles
Accessory muscles are recruited during exercise or when there is a dysfunction in the respiratory system. They are a double-domed musculotendinous sheet of internal skeletal muscle located at the inferior-most aspect of the rib cage that separates the thoracic cavity from the abdominal cavity.
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 potential to cause a breathing action. Muscles that help in expanding the thoracic cavity are called inspiratory muscles because they aid inhalation. Those that compress the thoracic cavity are called expiratory muscles and they induce exhalation.
The primary inspiratory muscles are the diaphragm and external intercostals. Normal expiration is a passive process that happens because of the elastic recoil of the lungs and surface tension. However, there are a few muscles that help in forceful expiration, including the internal intercostals, intercostalis intimi, subcostals, and the abdominal muscles. The rectus abdominis pulls the ribs down during active expiration. Its point of origin is the pubic symphysis and pubic crest, and it attaches to the xiphoid process and the 5th to 7th costal cartilages. The abdominal muscles help to expel air across the obstructed airways.
The accessory expiratory muscles are the abdominal muscles: rectus abdominis, external oblique, internal oblique, and transversus abdominis.
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Use of accessory muscles during normal breathing indicates an underlying problem
The use of accessory muscles during normal breathing is a sign that the respiratory system is under stress or that normal breathing mechanics are compromised. The diaphragm and intercostal muscles are the primary drivers of respiration. When the diaphragm and outer intercostal muscles are unable to move enough air in and out of the lungs, the accessory muscles of respiration are called into action.
Accessory muscles are typically used during intense physical exertion or specific situations like high altitude, and their temporary use can be considered normal. However, if someone is using their accessory muscles during regular breathing, it is generally a sign of an underlying problem. Conditions that affect a person's ability to breathe normally, such as pneumonia, pulmonary edema, or acute respiratory distress syndrome, can lead to the activation of accessory muscles during typical breathing.
The accessory muscles of inspiration are used when a person tries to take in a big breath or when there is a blockage that does not allow adequate air to pass through the throat and windpipe. These include the scalene, sternocleidomastoid, trapezius, and pectoralis major muscles. The accessory muscles of expiration are activated when a person tries to forcefully breathe out, such as when blowing out a candle. The main accessory muscles of expiration are the abdominal wall muscles, which, when contracted, push the diaphragm up into the chest, forcing more air out of the lungs.
If you or someone else notices that you seem to be working harder than usual to breathe, it is important to consult a doctor promptly. Treating the underlying cause can help reduce the use of these muscles. For example, if a person with COPD is using their accessory muscles to breathe, their doctor may recommend pursed-lip breathing to improve their ability to breathe out and decrease accessory muscle use.
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Frequently asked questions
Accessory muscles are those that assist, but do not play a primary role, in breathing. They are called into action when the diaphragm and outer intercostal muscles are unable to move enough air in and out of the lungs. Accessory muscles are not used during normal breathing and their use often indicates the presence of a disorder affecting a person's ability to breathe.
The accessory muscles of inspiration include the scalene, sternocleidomastoid, trapezius, and pectoralis major muscles. These muscles lift up the breastbone, upper ribs, and collarbones, causing the upper part of the chest to rise, making the lungs bigger, and allowing more air to enter.
The accessory muscles of expiration are the abdominal wall muscles. These muscles are used when a person tries to forcefully breathe out, such as when blowing out a candle. They are also used in disorders preventing normal movement of air out of the lungs, such as severe chronic obstructive pulmonary disease (COPD).
