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Accessory muscles are a relatively rare anatomical variation where a duplication of a muscle may appear anywhere in the muscular system. They are not typically used during normal breathing, but they are pivotal in maximising air intake when additional respiratory effort is required, such as during deep breathing or in response to respiratory challenges. Accessory muscles are also important in compensating for respiratory conditions such as hypoxemia, hypercapnia, and metabolic acidosis.
| Characteristics | Values |
|---|---|
| Definition | Relatively rare anatomical variation where duplication of a muscle may appear anywhere in the muscular system |
| Activation | Activated during deliberately deep breaths, forceful exhalation, or when a person has a condition that makes breathing more difficult |
| Function | Provide assistance to the main breathing muscles, mainly when additional power is needed, e.g., during exercise or for those with airway pathologies |
| Examples | Accessory soleus muscle, extensor digitorum brevis manus, epitrochleoanconeus muscle, sternalis muscle, axillary arch, pectoralis minor, subclavius |
| Clinical Use | Can be used in reconstructive surgery; recognition and evaluation can aid in diagnosis and treatment |
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What You'll Learn
- Accessory muscles are rarely used during regular breathing
- They are activated during deep breaths, e.g. during swimming or blowing out candles
- They are also used to compensate for respiratory conditions like COPD
- Accessory muscles are usually asymptomatic but can cause clinical symptoms
- They can be found in the pectoral region, e.g. pectoralis major or pectoralis minor
Accessory muscles are rarely used during regular breathing
Accessory muscles are not typically used during regular breathing for people in good health. The diaphragm is the only muscle used in normal breathing, and it contracts during inhalation. Normal exhalation is a passive process that relies on the diaphragm and the lungs' elastic recoil. However, accessory muscles become active during forced exhalation, such as when engaging in vigorous physical activity, coughing, or blowing out birthday cake candles. They are also used during deep breathing or in response to respiratory challenges.
Accessory muscles refer to muscles that provide assistance to the main breathing muscles when additional power is needed, such as during exercise or for those with respiratory conditions. These include the sternocleidomastoid, scalene, intercostal, abdominal, and pectoralis minor muscles. The sternocleidomastoid, located in the neck, lifts the sternum and enables increased expansion of the chest cavity, facilitating deep inhalation. The scalene muscles, also in the neck, assist in elevating the second and third ribs, further contributing to chest expansion during intensive breathing efforts. The pectoralis minor, located in the upper chest and front of the shoulders, elevates the third, fourth, and fifth ribs, enhancing chest expansion and increasing lung capacity during inhalation.
In addition to their role in breathing, accessory muscles can also be involved in neurovascular compression. For example, the sternocleidomastoid and scalene muscles can be used to evaluate respiratory neuromuscular weakness in patients with amyotrophic lateral sclerosis. Furthermore, accessory muscles may be used during specific life stages, such as in infants whose intercostal muscles are not yet fully developed, or in elderly individuals receiving end-of-life care.
Accessory muscles may also be activated in individuals with conditions that make breathing challenging, such as COPD, which can lead to hypoxemia or hypercapnia. In such cases, doctors may recommend techniques like pursed-lip breathing to help reduce reliance on accessory muscles. Overall, understanding the interplay between primary and accessory respiratory muscles is essential for diagnosing and treating respiratory conditions and improving respiratory health.
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They are activated during deep breaths, e.g. during swimming or blowing out candles
Accessory muscles are those that are not primarily responsible for movement but do provide assistance to the main muscles. They are also referred to as supernumerary muscles. Accessory muscles are usually asymptomatic and are only activated in specific scenarios.
In the context of breathing, accessory muscles are those other than the diaphragm that are activated during breathing. The diaphragm is the only muscle used during normal breathing, and it contracts during inspiration. Normal expiration is passive, relying on the elastic recoil of the lungs. Accessory muscles are activated during deep breaths, such as during swimming or blowing out birthday candles. They are also activated in people with conditions that make breathing more difficult, such as COPD, or in situations requiring forced exhalation, like coughing or vigorous physical activity.
Accessory muscles that are activated during deep breaths include the sternocleidomastoid, scalene, intercostal, and abdominal muscles. The sternocleidomastoid, located in the neck, lifts the sternum, allowing for increased expansion of the chest cavity during deep inhalation. The scalene muscles, also in the neck, assist in elevating the second and third ribs, further contributing to chest expansion. The pectoralis minor, located in the upper chest and front of the shoulders, helps elevate the third, fourth, and fifth ribs, enhancing chest expansion and increasing lung capacity during inhalation. Finally, the abdominal muscles are activated during forced exhalation, contracting to push up against the diaphragm and helping to expel air more forcefully.
In addition to their role in breathing, accessory muscles can also be implicated in neurovascular compression. For example, the accessory abductor digiti minimi muscle can cause ulnar nerve compression in Guyon's canal, leading to potential issues in the wrist and forearm.
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They are also used to compensate for respiratory conditions like COPD
Accessory muscles are additional muscles that the body activates to assist the primary breathing muscles in inhaling and exhaling air into the lungs. They are typically used when more power is needed, such as during exercise, or when dealing with airway pathologies like COPD.
COPD, or chronic obstructive pulmonary disease, is a condition that makes it harder to breathe due to increased airway resistance. This can lead to hyperinflation, where the lungs over-inflate and air becomes trapped. As a result, the diaphragm and intercostal muscles are at a disadvantage, unable to move enough air in and out of the lungs. This is known as respiratory muscle dysfunction and is a common feature of acute and chronic respiratory failure in COPD patients.
In response to the increased load, the diaphragm undergoes unique adaptations in its cellular structure and mechanical properties, becoming more efficient. There is also a shift towards slow-twitch, oxidative type I fibres, which increases the diaphragm's endurance. However, these changes may not be enough to compensate for the decreased capacity of the inspiratory muscles to generate pressure due to the mechanical disadvantage imposed by hyperinflation.
As a result of these factors, individuals with COPD may be forced to activate their accessory muscles for expiration. These accessory muscles help compensate for the reduced function of the diaphragm and intercostal muscles, aiding in the breathing process. The sternocleidomastoid and scalene muscles are commonly used as accessory muscles during inspiration, while the abdominal oblique muscles are primarily used during expiration.
It is important for individuals with COPD to seek medical advice if they find themselves relying on their accessory muscles for breathing. Doctors may recommend techniques such as pursed-lip breathing to help improve exhalation and reduce the need for accessory muscle use.
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Accessory muscles are usually asymptomatic but can cause clinical symptoms
Accessory muscles are those that are not primarily responsible for movement but do provide assistance to the main muscles, particularly during exertion. They are usually asymptomatic and are often incidental findings during surgery or imaging. However, in some cases, they can produce clinical symptoms.
Accessory muscles are typically not active during regular breathing for healthy individuals. They are engaged when a person takes a deliberately deep breath, such as when swimming underwater or blowing out birthday candles. In people with certain medical conditions, the body may automatically activate the accessory muscles during typical breathing. For example, those with COPD may experience shortness of breath, which can lead to the activation of accessory muscles for expiration. This is because the diaphragm and intercostal muscles are at a disadvantage due to over-inflation of the lungs, resulting in trapped air.
In addition, different life stages can influence the use of accessory muscles. For instance, newborns may recruit accessory muscles to help them breathe, as their intercostal muscles are not yet fully developed. Similarly, young children under general anaesthesia may experience a more significant deterioration in breathing compared to adults due to their inability to control their breathing to the same extent.
Accessory muscles can also be implicated in neurovascular compression, which has clinical relevance. For example, in the carpal tunnel, the median nerve may be compressed by accessory muscles, leading to potential symptoms. Thus, recognising and carefully evaluating accessory muscles can aid in diagnosis and treatment when symptoms are present.
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They can be found in the pectoral region, e.g. pectoralis major or pectoralis minor
Accessory muscles are relatively rare anatomical variations where a duplication of a muscle can appear anywhere in the muscular system. They are generally not treated unless they interfere with normal function.
The pectoral region, located on the anterior chest wall, is subject to a high degree of variability. It contains four muscles that exert a force on the upper limb: the pectoralis major, pectoralis minor, serratus anterior, and subclavius. The pectoralis major is the most superficial muscle in the pectoral region. It is large and fan-shaped, composed of a sternal head and a clavicular head. The sternal head originates from the anterior surface of the sternum, the superior six costal cartilages, and the aponeurosis of the external oblique muscle. The clavicular head originates from the anterior surface of the medial clavicle.
The pectoralis minor lies underneath the pectoralis major. It originates from the 3rd to 5th ribs and inserts into the coracoid process of the scapula. Its function is to stabilise the scapula by drawing it anteroinferiorly against the thoracic wall. The serratus anterior is located laterally in the chest wall and forms the medial border of the axilla region. It consists of several strips that originate from the lateral aspects of ribs 1-8 and attach to the costal surface of the medial border of the scapula. The subclavius is a small muscle located directly underneath the clavicle, running horizontally. It provides minor protection to the underlying neurovascular structures and anchors and depresses the clavicle.
Variations of the pectoralis minor include the pectoralis minimus, where one muscular slip passes from the first rib to the coracoid process. The pectoralis minor can also have costal attachments to the 2nd to 5th ribs, 3rd to 5th ribs, or 2nd to 4th ribs. In some cases, an accessory muscle may arise separately from the 5th and 6th ribs at the costochondral junction and fuse with the pectoralis minor. This accessory muscle can be distinguished from the pectoralis minor by its investing fascia and the position of the subcutaneous fascia.
The presence of accessory pectoral muscles can have both positive and negative implications. They may be useful in reconstructive surgery, but they can also be mistaken for masses or tumours during CT or MRI scans and cause difficulties during pectoral flap surgeries.
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Frequently asked questions
Accessory muscles are muscles that are not primarily responsible for movement but provide assistance to the main muscles, especially during vigorous physical activity.
Yes, accessory muscles for breathing refer to muscles that provide assistance to the main breathing muscles, mainly when additional power is required, for example, during exercise or in people with airway pathologies such as COPD.
Examples of accessory muscles for breathing include the sternocleidomastoid, scalene, intercostal, and abdominal muscles.
Accessory muscles are a relatively rare anatomical variation. In most cases, they are asymptomatic and are only found incidentally during surgery or imaging.
Accessory muscles can sometimes produce clinical symptoms and cause problems. For example, they may be related to a palpable swelling or compress nerves, such as in carpal tunnel syndrome.
