Dominic Stone
The intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces between the ribs. They are divided into three groups: external, internal, and innermost intercostals. All three groups of muscles support the rib cage and participate in the process of breathing by helping to expand and shrink the chest cavity. The external intercostals facilitate forced inspiration, while the internal and innermost intercostals aid in forced expiration. Deficient intercostal muscles can lead to respiratory insufficiency.
| Characteristics | Values |
|---|---|
| Definition | Group of intrinsic rib cage muscles that occupy the 11 intercostal spaces |
| Types | External intercostals, Internal intercostals, Innermost intercostals |
| Function | Accessory respiratory muscles that participate in the process of forced breathing |
| Origin | External intercostals originate from the inferior border of one rib, Internal intercostals originate from the costal groove of one rib |
| Insertion | External intercostals insert to the superior border of the rib below, Internal intercostals insert to the superior border of the immediate rib below |
| Innervation | External and Internal intercostals are innervated by the intercostal nerves |
| Blood Supply | Internal intercostals receive blood supply from anterior and posterior intercostal arteries, costocervical trunk, internal thoracic and musculophrenic arteries |
| Action | External intercostals elevate the ribs, Internal intercostals depress the ribs |
| Direction of Muscle Fibres | External intercostals: downward, forward and medial, Internal intercostals: downward, forward and lateral |
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What You'll Learn
- The internal intercostal muscles are responsible for depressing the ribs during forced expiration
- The external intercostal muscles elevate the ribs, aiding quiet and forced inhalation
- Intercostal muscles support the rib cage and are accessory respiratory muscles
- Deficient intercostal muscles can lead to respiratory insufficiency
- The internal and external intercostal muscles have a similar effect on the ribs
The internal intercostal muscles are responsible for depressing the ribs during forced expiration
The intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces between the ribs. They are divided into three groups, from superficial to deep: external intercostals, internal intercostals, and innermost intercostals. All three groups of muscles support the rib cage and are accessory respiratory muscles that participate in the process of forced breathing.
The internal intercostal muscles 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 rib below. The function of these muscles is to depress the ribs during forced expiration.
During forced expiration, the internal intercostal muscles contract and pull the ribs downward and inward, reducing the transverse dimensions of the thoracic cavity. This contraction of the internal intercostal muscles aids in forcing air out of the lungs during exhalation.
The internal intercostal muscles are innervated by the intercostal nerves and receive their blood supply from multiple arteries, including the anterior and posterior intercostal arteries, the costocervical trunk, the internal thoracic artery, and the musculophrenic artery.
In contrast, the external intercostal muscles facilitate forced inspiration by elevating and expanding the ribs, thus increasing the size of the thoracic cavity. The internal and innermost intercostal muscles work together with the external intercostal muscles to regulate the volume of the thoracic cavity, allowing for efficient inhalation and exhalation during respiration.
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The external intercostal muscles elevate the ribs, aiding quiet and forced inhalation
The intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces. They are divided into three groups: internal, external, and innermost. The external intercostal muscles, also known as intercostalis externus, aid in quiet and forced inhalation. They originate on ribs 1–11 and insert on ribs 2–12. The muscle fibres are directed downwards, forwards, and medially in the anterior part.
The external intercostals are responsible for elevating the ribs and bending them more open, thus expanding the transverse dimensions of the thoracic cavity. This expansion increases the volume of the chest cavity, facilitating inhalation. The external intercostals are the most superficial intercostal muscles, and their function in inhalation is supported by their anatomical structure. They originate from the inferior border of one rib and insert onto the superior border of the rib below, following a diagonal path. This diagonal path allows for a greater range of motion during contraction, as longer muscles can shorten more significantly than shorter, vertical muscles.
The internal intercostal muscles, or intercostalis internus, aid in forced exhalation, while quiet exhalation is a passive process. They originate on ribs 2–12 and insert on ribs 1–11. The internal intercostals depress the ribs and bend them inward, decreasing the transverse dimensions of the thoracic cavity. This action reduces the volume of the chest cavity, assisting in forced exhalation. The internal intercostals form the middle layer of the intercostal musculature, located inside the rib cage.
While the conventional understanding is that the external and internal intercostals have opposing functions, with the external intercostals elevating the ribs and the internal intercostals lowering them, recent studies have challenged this notion. These studies suggest that when acting alone, both types of intercostals have a similar effect on the ribs, elevating them and increasing the volume of the thoracic cavity. However, it is important to note that these studies were conducted on anesthetised dogs, and the results may vary in other contexts.
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Intercostal muscles support the rib cage and are accessory respiratory muscles
The intercostal muscles are intrinsic rib cage muscles that occupy the 11 intercostal spaces between the ribs. They are divided into three groups: external, internal, and innermost intercostals. All three groups of muscles support the rib cage and are accessory respiratory muscles that participate in the process of breathing.
The external intercostals are the most superficial intercostal muscles. They originate from the inferior border of one rib and insert into the superior border of the rib below. These muscles facilitate forced inspiration, elevating the ribs and bending them open to expand the thoracic cavity.
The internal intercostals form the middle layer of the intercostal musculature. They originate from the costal groove of one rib and insert into the superior border of the rib below. These muscles aid in forced expiration by depressing the ribs and bending them inward to decrease the thoracic cavity size.
The innermost intercostals are the deepest intercostal muscles, separated from the internal intercostals by a neurovascular bundle. Their muscle fibres are directed downwards, forwards, and laterally, similar to the internal intercostal muscles.
The external and internal intercostals have a similar effect on the ribs, and their action is influenced by the rib cage volume. The lateral intercostals, another type of intercostal muscle, may be more involved in postural movements than respiration, as they play a role in trunk rotations.
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Deficient intercostal muscles can lead to respiratory insufficiency
The intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces between the ribs. They are divided into three groups, from superficial to deep: 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 originate from the inferior border of one rib, course inferomedially, and insert into the superior border of the immediate rib below. They facilitate forced inspiration, aiding in quiet and forced inhalation. The muscle fibres are directed downwards, forwards, and medially in the anterior part.
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. They aid in forced expiration, depressing the ribs and bending them inward to decrease the transverse dimensions of the thoracic cavity.
The innermost intercostals are the deepest intercostal muscles, separated from the internal intercostals by a neurovascular bundle. Their muscle fibres are directed in the same way as the internal intercostals.
Deficient intercostal muscles, such as those caused by neuromuscular diseases, may result in respiratory insufficiency. The intercostal muscles play a crucial role in the mechanical aspect of breathing by helping to expand and shrink the chest cavity. They facilitate both inspiration and expiration, working in coordination with other respiratory muscles. When these muscles are deficient, they may not provide the necessary tension to the intercostal spaces, leading to internal and external movements of the chest wall during thoracic pressure changes. This disruption in the normal functioning of the intercostal muscles can impair the respiratory process, resulting in respiratory insufficiency.
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The internal and external intercostal muscles have a similar effect on the ribs
The intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces between the ribs. They are divided into three groups, from superficial to deep: external intercostals, internal intercostals, and innermost intercostals. All three groups of muscles support the rib cage and are accessory respiratory muscles that participate in the process of breathing.
The external intercostal muscles, also known as intercostalis externus, aid in quiet and forced inhalation. They originate from the inferior border of one rib and insert onto the superior border of the rib below. The external intercostals elevate the ribs and bend them more open, expanding the thoracic cavity.
The internal intercostal muscles, or intercostalis internus, aid in forced expiration. They originate from the costal groove of one rib and insert onto the superior border of the rib below. The internal intercostals depress the ribs and bend them inward, decreasing the thoracic cavity.
Despite their opposite functions in inhalation and exhalation, studies have shown that the internal and external intercostal muscles have a similar effect on the ribs. When contracting in a single interspace while other muscles are relaxed, both muscle groups exhibit a net rib-elevating action at end-expiratory rib cage volume. This effect is dependent on rib cage (lung) volume and is influenced by the resistance of the upper and lower ribs to displacement.
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Frequently asked questions
The intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces between the ribs. They are divided into three groups: external, internal, and innermost intercostals. All three groups support the rib cage and are accessory respiratory muscles.
The external intercostal muscles facilitate forced inspiration during breathing, while the internal intercostals aid in forced expiration by depressing the ribs and bending them inward. The innermost intercostal muscles are deep layers of the internal intercostal muscles, separated by a neurovascular bundle.
The external intercostal muscles take a downward and outward path when viewed from the back. They elevate the ribs, expanding the thoracic cavity. In contrast, the internal intercostal muscles extend from the front of the ribs, going around the back, and lower the ribs, decreasing the thoracic cavity.
