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Accessory muscles are additional muscles that the body uses to help inhale and exhale air into the lungs. They are also known as breathing pump muscles. They are recruited during exercise or when there is a dysfunction in the respiratory system. Accessory muscles of inspiration lift the third, fourth, and fifth ribs to increase space for air in the lungs. These include the sternocleidomastoid, the scalenus anterior, medius, and posterior, the pectoralis major and minor, and the serratus anterior, among others.
| Characteristics | Values |
|---|---|
| Main inspiratory muscle | Diaphragm |
| Action | Diaphragm contracts and moves inferiorly, increasing the vertical diameter of the thoracic cavity and producing lung expansion |
| Accessory inspiratory muscles | Sternocleidomastoid, scalenus anterior, medius, and posterior, pectoralis major and minor, inferior fibres of serratus anterior and latissimus dorsi, serratus posterior superior, iliocostalis cervicis |
| Function of accessory inspiratory muscles | Increase the size of the thoracic cavity by pulling the sternum and first two ribs |
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What You'll Learn
Accessory muscles are used during exercise or respiratory dysfunction
Accessory muscles are recruited during exercise due to increased metabolic need. They are also used during respiratory dysfunction. These muscles are also called the 'breathing pump muscles' and form a complex arrangement in the form of semi-rigid bellows around the lungs. All muscles attached to the human rib cage can cause a breathing action. Muscles that help expand the thoracic cavity are called inspiratory muscles because they aid inhalation. Conversely, muscles that compress the thoracic cavity are expiratory muscles, which induce exhalation.
The diaphragm is the main inspiratory muscle. During inspiration, it contracts and moves in an inferior direction, increasing the vertical diameter of the thoracic cavity and causing lung expansion, which draws air in. The diaphragm has three types of muscles: external intercostal muscles, internal intercostal muscles, and innermost intercostal muscles.
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. Any muscle attached to the upper limb and the thoracic cage can act as an accessory muscle of inspiration through reverse muscle action.
Accessory expiratory muscles are the abdominal muscles: rectus abdominis, external oblique, internal oblique, and transversus abdominis. In the thoracolumbar region, the lowest fibres of iliocostalis and longissimus, the serratus posterior inferior and quadratus lumborum are also accessory expiratory muscles.
During exercise, accessory muscles increase the size of the thoracic cavity even more by further pulling the sternum and first two ribs. They are also used during respiratory distress due to airway obstructions.
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The diaphragm is the main inspiratory muscle
The diaphragm is the primary muscle responsible for inhalation, or inspiration. During inspiration, the diaphragm contracts and moves inferiorly, increasing the vertical diameter of the thoracic cavity and causing the lungs to expand. This contraction draws air into the lungs. When the diaphragm relaxes, the lungs elastically recoil, causing the thoracic cavity to contract and forcing air out of the lungs.
The diaphragm is a thin, dome-shaped muscle that separates the abdominal cavity from the thoracic cavity. It is involved in non-respiratory functions, such as expelling vomit, faeces, and urine from the body, and preventing acid reflux.
While the diaphragm is the main inspiratory muscle, there are also accessory inspiratory muscles that can be called upon during times of increased metabolic need, such as exercise, or during respiratory dysfunction. These accessory muscles include the sternocleidomastoid, scalenus anterior, medius, and posterior, pectoralis major and minor, and serratus anterior, among others. Accessory muscles help to elevate the ribs and sternum, increasing the volume of the thoracic cavity and facilitating deeper inhalation.
In healthy individuals, accessory muscles are typically not active during normal breathing. However, they may be engaged during deep inhalation, such as when swimming underwater or blowing out birthday candles. Additionally, people with respiratory conditions may rely more on their accessory muscles during typical breathing to compensate for their breathing difficulties.
The intercostal muscles, which consist of external, internal, and innermost layers, are another important group of respiratory muscles that assist in inspiration and expiration. These muscles are attached between the ribs and help manipulate the width of the rib cage.
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Intercostal muscles are important in respiration
The intercostal muscles are a group of muscles attached between the ribs and are important in respiration as they aid inhalation by manipulating the width of the rib cage. There are three layers of intercostal muscles: external, internal, and innermost. The external intercostal muscles are the most important in respiration. These muscles have fibres that are angled obliquely downward and forward 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 intercostal muscles are accessory muscles, which are additional muscles the body activates to help inhale and exhale air into the lungs. Accessory muscles assist in breathing but do not play a primary role. They are typically used during deep breathing, such as during exercise, swimming underwater, or forcefully expelling air. They are also used by those with respiratory conditions that make breathing more difficult, such as COPD, and during certain life stages, such as in infancy.
The diaphragm is the main inspiratory muscle, contracting and moving downward during inspiration, increasing the vertical diameter of the thoracic cavity, and producing lung expansion. The diaphragm is considered the major muscle responsible for breathing, separating the abdominal cavity from the thoracic cavity. During inhalation, the diaphragm contracts, moving its centre downward and its edges upward, compressing the abdominal cavity, raising the ribs, and expanding the thoracic cavity.
The intercostal muscles assist the diaphragm in this process, and their elasticity is crucial to the health of the respiratory system. The internal intercostal muscles have fibres that are angled obliquely downward and backward from rib to rib. These muscles also assist in forceful expiration, along with the intercostalis intimi, subcostals, and abdominal muscles.
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Scalenus anterior, medius, and posterior are accessory inspiratory muscles
The scalenus anterior, medius, and posterior are accessory inspiratory muscles, also known as breathing pump muscles. They are three of the scalene muscles, which are found on each side of the neck. These muscles are involved in breathing and play a role in inspiration, elevating the ribs during forced inspiration.
The scalenus anterior is the anteriormost of the three scalene muscles, originating from the anterior tubercles of the transverse processes of the vertebrae C3-C6. It contributes to the elevation of the first rib. When the attachment to the vertebral column is fixed, the scalenus anterior can lift the first rib superiorly. This action, combined with the contraction of the external intercostal muscles, expands the antero-posterior diameter of the thorax.
The scalenus medius is the largest and longest of the scalene muscles. It originates from the transverse processes of the axis (C2), transverse processes of the atlas (C1), and the posterior tubercles of the transverse processes of the vertebrae C3-C7. The scalenus medius is covered by the sternocleidomastoid muscle, and its anterolateral surface is pierced by the dorsal scapular nerve. It is the most significant for breathing in the scalene group.
The scalenus posterior passes from the posterior tubercles of the transverse process of C4-6 to the second rib, helping to elevate it. The scalenus medius forms the posterior border of the interscalene triangle, while the scalenus anterior forms the anterior border. The scalene muscles facilitate accessory breathing and contribute to neck and head movement, as well as postural stability between the neck and head.
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Accessory muscles are activated in people with COPD
Accessory muscles are recruited during exercise or when there is a dysfunction in the respiratory system. They are also called the 'breathing pump muscles' and form a complex arrangement around the lungs. The diaphragm is the main inspiratory muscle, and during inspiration, it contracts and moves in an inferior direction, increasing the vertical diameter of the thoracic cavity and causing lung expansion.
People with chronic obstructive pulmonary disease (COPD) often experience muscle dysfunction, including deficits in muscle strength, mass, quality, and mobility. This can lead to ventilatory insufficiency and limit their exercise capacity and daily activities.
A study on the effects of breathing maneuvers and sitting posture on muscle activity in inspiratory accessory muscles in patients with COPD found that pursed-lips breathing (PLB) significantly increased tidal volume (TV) and decreased respiratory rate (RR) compared to quiet natural breathing (QB). The scalenus (SM), sternocleidomastoid (SCM), and pectoralis major (PM) muscles were specifically examined in this study.
The accessory inspiratory muscles include the sternocleidomastoid, scalenus anterior, medius, and posterior, pectoralis major and minor, and the serratus anterior, among others. These muscles are activated in people with COPD to compensate for the dysfunction in their respiratory system.
In summary, accessory muscles are activated in people with COPD due to the increased demand on their respiratory system. This activation helps to increase the size of the thoracic cavity, elevate the ribs and sternum, and ultimately improve breathing in these individuals.
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Frequently asked questions
Accessory muscles for inspiration include the sternocleidomastoid, scalenus anterior, medius, and posterior, pectoralis major and minor, serratus anterior, and latissimus dorsi.
The diaphragm is the main inspiratory muscle.
During inspiration, the diaphragm contracts and moves downward, increasing the vertical diameter of the thoracic cavity and expanding the lungs, which draws air into the lungs.
Accessory muscles of respiration are muscles that assist but do not play a primary role in breathing. The sternocleidomastoid and the scalenes (anterior, middle, and posterior) are typically included.
Accessory muscles for inspiration are used during exercise or when there is a dysfunction in the respiratory system. They are also used when taking a deliberately deep breath, such as when swimming underwater or blowing out birthday cake candles.
