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Accessory muscles are supplementary muscles that are activated to help the body inhale and exhale air into the lungs. They are typically associated with severe obstructive disease and are used by more than 90% of patients hospitalized with acute exacerbations of chronic obstructive pulmonary disease (COPD). Accessory muscles are also used during exercise due to increased metabolic need and during dysfunction in the respiratory system. They can be found in the neck, thorax, pelvis, and upper and lower limbs.
| Characteristics | Values |
|---|---|
| Definition | Accessory muscles are supplementary discrete muscles that are found alongside the normal expected musculature. |
| Location | Accessory muscles have been described in the neck, thorax, pelvis, upper and lower limbs. |
| Function | Accessory muscles are not active during regular breathing for people in good health. However, they are used during deep breaths, exercise, or when the respiratory system is dysfunctional. |
| Types | Accessory muscles of respiration include the sternocleidomastoid, the scalene muscles (anterior, middle, and posterior), the trapezius, and the external intercostals. |
| Anatomical Variation | Accessory muscles are a rare anatomical variation where duplication of a muscle may appear anywhere in the muscular system. Examples include the accessory soleus muscle in the calf or ankle, the extensor digitorum brevis manus in the hand, and the pectoralis major or pectoralis minor, which may be doubled or absent. |
| Treatment | Treatment is generally not required for accessory muscles unless they interfere with normal function. |
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What You'll Learn
- Accessory muscles are supplementary muscles that help with inspiration and expiration
- They are found in the neck, thorax, pelvis, and limbs
- Accessory muscles are used when breathing difficulties arise
- They are also used during exercise due to increased metabolic need
- Examples include the sternocleidomastoid and scalene muscles
Accessory muscles are supplementary muscles that help with inspiration and expiration
Accessory muscles are supplementary muscles that help with inspiration (breathing in) and expiration (breathing out). They are additional muscles that the body activates to assist in inhaling and exhaling air into the lungs. Accessory muscles are typically not used during normal breathing in healthy individuals, but they may be recruited during exercise, when taking a deep breath, or when a person has a respiratory condition that makes breathing more difficult.
The diaphragm is the primary muscle responsible for inspiration, and normal expiration is a passive process that occurs due to the elastic recoil of the lungs. Accessory muscles are used during inspiration when there is severe obstructive disease, and their use can be a sign of respiratory muscle fatigue or conditions such as chronic obstructive pulmonary disease (COPD). In newborns, accessory muscles are recruited when the diaphragm fatigues, as it is not yet fully developed.
Examples of accessory muscles of inspiration include the sternocleidomastoid, scalenus anterior, serratus anterior, and pectoralis major. These muscles help to lift the ribs to increase space for air in the lungs. Accessory muscles of expiration include the abdominal muscles, such as the rectus abdominis and external oblique.
Accessory muscles can also refer to anatomical variations where a duplication of a muscle appears in the muscular system. These accessory muscles are not typically involved in movement but may provide assistance. Examples include the accessory soleus muscle in the calf or ankle and the extensor digitorum brevis manus in the hand.
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They are found in the neck, thorax, pelvis, and limbs
Accessory muscles are supplementary muscles that are found alongside the normal expected musculature. They are a form of anatomical variation, where a duplication of a muscle may appear anywhere in the muscular system. These muscles are not typically active during regular breathing for a person in good health. However, they may be used when taking a deep breath, such as when swimming underwater or blowing out birthday candles.
Accessory muscles are found in the neck, thorax, pelvis, and limbs. In the neck, examples of accessory muscles include the sternocleidomastoid and scalene muscles (anterior, middle, and posterior scalene), which are considered accessory muscles of respiration. The pectoralis major and minor, the trapezius, and the external intercostals are also accessory muscles of respiration, found in the thorax.
The pelvis and limbs also contain accessory muscles, such as the accessory soleus muscle in the calf or ankle, the extensor digitorum brevis manus in the hand, and the epitrochleoanconeus muscle of the upper arm. In the hand, the flexor carpi radialis brevis can compress the anterior interosseous nerve. On the extensor side, there are the extensor digitorum brevis manus, extensor carpi radialis intermedius, and extensor medii proprius muscles.
Accessory muscles can be useful in certain medical contexts. For example, the chondrocoracoideus has potential for use in reconstructive surgery, and awareness of axillary accessory muscles can be important during axillary lymph node removal to avoid complications.
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Accessory muscles are used when breathing difficulties arise
Accessory muscles are supplementary muscles that are not typically used during normal breathing. However, they are recruited during breathing difficulties, such as in patients with chronic obstructive pulmonary disease (COPD) or respiratory muscle fatigue. These accessory muscles assist in inhalation and exhalation, ensuring adequate ventilation when the primary respiratory muscles are compromised.
The diaphragm is the primary muscle responsible for inspiration, and during normal breathing, it is the only muscle required for this process. However, in individuals with respiratory conditions, the diaphragm may not be sufficient to facilitate adequate ventilation. This is when the accessory muscles of inspiration are called upon to assist in lifting the ribs and expanding the thoracic cavity, creating more space for the lungs to fill with air. Examples of accessory inspiratory muscles include the sternocleidomastoid, scalene muscles, serratus anterior, and pectoralis major, among others.
Expiration, or exhalation, is typically a passive process that relies on the elastic recoil of the lungs. However, during breathing difficulties, accessory expiratory muscles may be engaged to forcefully expel air. These muscles include the abdominal muscles, such as the rectus abdominis and internal oblique, as well as the intercostal muscles. The activation of these accessory muscles during expiration can be observed in patients with respiratory conditions, indicating the presence of breathing difficulties.
Accessory muscles can also be utilised during certain activities that require increased respiratory effort, such as exercising or swimming underwater. In these situations, the body may automatically engage the accessory muscles to meet the increased metabolic demand and ensure adequate ventilation. Additionally, during periods of metabolic acidosis, when there is excessive acid in the bodily fluids, accessory muscles can be used to compensate and maintain proper ventilation.
Furthermore, accessory muscles may be activated during certain life stages, such as in infants or end-of-life care. For example, newborns may recruit accessory muscles due to the relative weakness and fatigue of their diaphragm, which is not yet fully developed. Similarly, in end-of-life care, breathing difficulties may arise, leading to the activation of accessory muscles as the body strives to maintain adequate ventilation.
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They are also used during exercise due to increased metabolic need
Accessory muscles are supplementary muscles that are not primarily responsible for movement but can be used to assist other muscles during exercise or when the body has an increased metabolic need. They are also known as breathing pump muscles as they can help with inhalation and exhalation.
Accessory muscles are recruited during exercise due to increased metabolic need. During exercise, the body requires more oxygen, and accessory muscles can help expand the thoracic cavity, allowing for deeper inhalation. Examples of accessory muscles include the sternocleidomastoid and scalene muscles, which are often used during inspiration in people with severe obstructive disease.
In healthy individuals, accessory muscles are not typically active during normal breathing. However, they may be used during exercise or when taking a deep breath, such as when swimming underwater or blowing out birthday candles. Accessory muscles can also be activated during typical breathing in people with respiratory conditions, such as chronic obstructive pulmonary disease (COPD), where the diaphragm and intercostal muscles are at a disadvantage due to over-inflation of the lungs.
Accessory muscles can be found in various parts of the body, including the neck, thorax, pelvis, and upper and lower limbs. They can also refer to duplicate muscles that appear anywhere in the muscular system, such as the accessory soleus muscle in the calf or ankle.
The use of accessory muscles during exercise can be beneficial in meeting the increased metabolic demand of the body. By assisting with breathing, these muscles help ensure that the body receives the oxygen it needs during physical activity. This can be particularly important for individuals with respiratory conditions, where the accessory muscles may be used to compensate for any breathing difficulties.
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Examples include the sternocleidomastoid and scalene muscles
An accessory muscle is a relatively rare anatomical variation where a duplication of a muscle may appear anywhere in the muscular system. Treatment is generally not required unless the accessory muscle interferes with normal bodily functions. Accessory muscles of respiration include the sternocleidomastoid and scalene muscles.
The sternocleidomastoid muscle (SCM) is one of over 20 pairs of muscles acting on the neck. It is a unique muscle in terms of variations at its origin and has a variable innervation arrangement. The SCM is a large, easily recognisable, and palpable muscle that divides the neck into anterior and posterior triangles. It is also an important anatomical landmark within the neck region and plays a role in neuromuscular pathologies such as torticollis. The SCM acts in concert with the entire muscular group of the cervicofacial region, aiding in various complex physiological movements beyond its principal function as a lateral neck flexor.
The scalene muscles, on the other hand, are three paired muscles of the lateral neck: the anterior, middle, and posterior scalene. The anterior scalene muscle is located deep to the sternocleidomastoid, while the trunks of the brachial plexus are visible between the anterior and middle scalene muscles. The brachial plexus can be infiltrated with local anaesthetic in upper limb surgery to avoid the use of general anaesthesia. The posterior scalene is the smallest and deepest of the scalene muscles, inserting into the second rib.
Both the sternocleidomastoid and scalene muscles are accessory inspiratory muscles. They contract during inspiration in patients with severe obstructive disease, particularly those with chronic obstructive lung disease or respiratory muscle fatigue. These accessory muscles are recruited during exercise due to increased metabolic need and during dysfunction in the respiratory system.
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Frequently asked questions
Accessory muscles are supplementary muscles that are found alongside the normal expected musculature. They are additional muscles that the body activates to help inhale and exhale air into the lungs.
Accessory muscles have been found in the neck, thorax, pelvis, upper and lower limbs.
Examples of accessory muscles include the scalene, the sternocleidomastoid, the pectoralis major, the trapezius, and the external intercostals.
Accessory muscles are used when the body requires more air than usual, such as during exercise or when experiencing respiratory dysfunction. They are also used when the primary muscles for breathing, such as the diaphragm, are not sufficient, as in the case of infants or patients with COPD.
The pectoralis major or pectoralis minor may be absent, or in some cases, the pectoralis major may be doubled. Other variants of accessory muscles in the pectoral region include the chondroepitrochleas and the costocoracoideus.
