Logan Steele
The intercostal muscles are a group of intrinsic rib cage muscles occupying the 11 intercostal spaces. They are divided into three groups: external, internal, and innermost intercostal muscles. These muscles are accessory respiratory muscles that support the rib cage and participate in the process of forced breathing. The external intercostals facilitate forced inspiration, while the internal and innermost intercostals aid forced expiration. Accessory muscles are recruited during exercise or respiratory dysfunction to maximise air intake and ensure sufficient oxygen reaches the bloodstream.
| Characteristics | Values |
|---|---|
| Definition | Accessory muscles are recruited during exercise or when there is a dysfunction in the respiratory system. |
| Location | Intercostal muscles occupy the 11 intercostal spaces. |
| Types | External, internal, and innermost intercostal muscles. |
| Function | Accessory muscles aid in respiration by maximising air intake and ensuring enough oxygen reaches the bloodstream. |
| Main Inspiratory Muscles | Diaphragm, external intercostal, and scalene muscles. |
| Accessory Inspiratory Muscles | Sternocleidomastoid, scalenus anterior, medius, and posterior, pectoralis major and minor, serratus anterior, and latissimus dorsi. |
| Accessory Expiratory Muscles | Abdominal muscles: rectus abdominis, external oblique, internal oblique, and transversus abdominis. |
| Nerve Supply | Motor nerve supply by the phrenic nerve and sensory supply by the phrenic nerve to the central tendon and lower intercostal nerve to peripheral parts. |
| Blood Supply | Inferior phrenic arteries, superior phrenic, anterior and posterior intercostal arteries, internal thoracic, and musculophrenic arteries. |
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What You'll Learn
Intercostals are accessory respiratory muscles
The intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces. They are accessory respiratory muscles that participate in the process of forced breathing. The three types of intercostal muscles are the external, internal, and innermost intercostal muscles. The external intercostals are the most superficial intercostal muscles and facilitate forced inspiration. The internal and innermost intercostals aid in forced expiration. All three groups of muscles support the rib cage.
The diaphragm is the main inspiratory muscle, contracting and moving in an inferior direction to increase the vertical diameter of the thoracic cavity and produce lung expansion. During inspiration, the diaphragm contracts and moves downward, increasing the volume of the thoracic cavity and drawing air into the lungs. The diaphragm is also involved in forced exhalation, contracting to expel air from the lungs more forcefully.
The accessory inspiratory muscles are the sternocleidomastoid, scalenus anterior, medius, and posterior, pectoralis major and minor, inferior fibres of serratus anterior and latissimus dorsi, and the serratus posterior superior. These muscles are crucial when additional respiratory effort is required, such as during deep breathing or in response to respiratory challenges. For example, the sternocleidomastoid lifts the sternum, facilitating an increased expansion of the chest cavity, which is vital for deep inhalation. 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.
The accessory expiratory muscles are the abdominal muscles, including the rectus abdominis, external oblique, internal oblique, and transversus abdominis. These muscles are actively engaged during situations requiring forced exhalation, such as vigorous physical activity or coughing. They contract to push up against the diaphragm, aiding in more forceful expulsion of air from the lungs.
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They aid in forced breathing
The intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces. They are divided into three groups: external, internal, and innermost intercostal muscles. All three groups of muscles support the rib cage and are accessory respiratory muscles that participate in the process of forced breathing.
The external intercostals are the most superficial intercostal muscles. They facilitate forced inspiration by elevating the ribs and sternum, increasing the vertical diameter of the thoracic cavity and producing lung expansion. This, in turn, draws air into the lungs.
The internal and innermost intercostals aid in forced expiration by depressing the ribs, reducing the space in the chest cavity and facilitating the forceful expulsion of air from the lungs.
The accessory muscles are recruited during exercise due to the increased metabolic need and during dysfunction in the respiratory system. They are also crucial during deep breathing or in response to respiratory challenges, such as coughing or an asthma attack. These muscles optimise lung function by aiding in significant lung expansion.
For example, the sternocleidomastoid, located in the neck, lifts the sternum, facilitating an increased expansion of the chest cavity, which is vital for deep inhalation. The scalene muscles, also located 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, helps to elevate the third, fourth, and fifth ribs, enhancing chest expansion and increasing lung capacity during inhalation.
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They are divided into three groups
The intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces. They are divided into three groups, namely the external, internal, and innermost intercostal muscles.
The external intercostals are the most superficial set of muscles that occupy the 11 intercostal spaces. They are the most superficial intercostal muscles, found superficially to the internal and innermost intercostals. They originate from the inferior border of one rib, course inferomedially, and insert themselves to the superior border of the immediate rib below. They are innervated by the anterior rami of spinal nerves T1-T11, i.e., the intercostal nerves of the corresponding intercostal space. The external intercostals are supplied by the muscular branches of the anterior and posterior intercostal arteries. The first two posterior intercostal arteries arise from the supreme intercostal artery, a branch of the costocervical trunk, while the remaining nine arise from the posterior aspect of the thoracic aorta. The external intercostals are one of the accessory respiratory muscles, elevating the ribs during forced inspiration and increasing the transverse and anteroposterior diameter of the lungs. This decreases the intrapleural pressure, expanding the lungs and facilitating the entry of air into them.
The internal intercostals form the middle layer of the intercostal musculature. They originate from the costal groove of one rib, course inferolaterally, and insert themselves to the superior border of the immediate rib below. They are innervated in the same way as the external intercostals, by the intercostal nerves. Their blood supply comes from the anterior and posterior intercostal arteries, as well as from the costocervical trunk, internal thoracic, and musculophrenic arteries. The internal intercostals are also accessory respiratory muscles, assisting breathing and supporting the integrity of the thoracic cage. They share the common functions of other muscles occupying the intercostal spaces, i.e., the external and innermost intercostal muscles. The internal intercostals depress the ribs during forced expiration, enabling forced expiration by depressing the ribs and shrinking the diameter of the thoracic cavity, thus pushing air out of the lungs.
The innermost intercostals are the deepest intercostal muscles. They assist in the depression of ribs during forced expiration. The vascularization and innervation of the innermost intercostals follow the same pattern as the internal intercostals, with blood supply coming from the anterior and posterior intercostal arteries, costocervical trunk, internal thoracic, and musculophrenic arteries. All three groups of intercostal muscles support the rib cage and are accessory respiratory muscles that participate in the process of forced breathing. The external intercostals facilitate forced inspiration, while the internal and innermost intercostals aid forced expiration.
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They support the rib cage
The intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces. They are divided into three groups: external, internal, and innermost intercostal muscles. All three groups of muscles support the rib cage.
The external intercostals are the most superficial intercostal muscles. They originate from the inferior border of one rib, course inferomedially, and insert into the superior border of the immediate rib below. The function of the external intercostals is to facilitate forced inspiration.
The internal intercostals form the middle layer of the intercostal musculature. They originate from the costal groove of one rib, course inferolaterally, and insert into the superior border of the immediate rib below. The internal intercostals aid in forced expiration by depressing the ribs.
The innermost intercostals are the deepest intercostal muscles. They also help with forced expiration.
Deficient intercostal muscles may not provide appropriate tension to the intercostal spaces, leading to internal and external chest wall movements during thoracic pressure changes and resulting in respiratory insufficiency.
The intercostal muscles are accessory respiratory muscles that participate in the process of forced breathing. They optimise lung function by aiding in lung expansion, which increases the volume of the thoracic cavity during respiration.
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They optimise lung function
The intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces. They are divided into three groups: external, internal, and innermost intercostal muscles. These muscles support the rib cage and are accessory respiratory muscles that participate in the process of forced breathing.
The external intercostals are the most superficial intercostal muscles and facilitate forced inspiration. They originate from the inferior border of one rib and insert themselves into the superior border of the immediate rib below. The internal intercostals form the middle layer of the intercostal musculature and depress the ribs during forced expiration. The innermost intercostals are the deepest intercostal muscles.
The intercostal muscles, along with other accessory muscles, optimise lung function by aiding in lung expansion. During normal exhalation, the primary muscles, such as the diaphragm and intercostal muscles, relax, reducing the space in the chest cavity and facilitating the expulsion of air from the lungs. In situations requiring forced exhalation, such as vigorous physical activity or coughing, accessory muscles, particularly the abdominal muscles, are actively engaged to help expel air more forcefully.
Accessory muscles are also crucial when additional respiratory effort is required, such as during deep breathing or in response to respiratory challenges like asthma attacks. For example, the sternocleidomastoid muscle, located in the neck, lifts the sternum, facilitating increased expansion of the chest cavity, which is vital for 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, helps to elevate the third, fourth, and fifth ribs, enhancing chest expansion and increasing lung capacity during inhalation.
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Frequently asked questions
Intercostal muscles occupy the 11 intercostal spaces and are divided into three groups: external, internal, and innermost intercostal muscles. They are a group of intrinsic rib cage muscles that support the rib cage and are accessory respiratory muscles that participate in the process of forced breathing.
Accessory muscles are muscles that aid respiratory efforts. They are used during strenuous activity requiring high physiological demand, such as exercise, or even singing. They are also used in situations requiring forced exhalation, such as vigorous physical activity or coughing.
Examples of accessory muscles include the scalene muscles, sternocleidomastoid muscles, internal intercostals, transversus thoracis, pectoralis major and minor muscles, serratus anterior, serratus posterior superior and inferior, latissimus dorsi, trapezius, and the muscles of the abdomen.
The external intercostals facilitate forced inspiration, while the internal and innermost intercostals aid forced expiration. They are responsible for changing the volume of the thoracic cavity during respiration.
