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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 layers: external intercostals, internal intercostals, and innermost intercostals. These muscles support the rib cage and assist in breathing, with the external intercostals facilitating inspiration and the internal and innermost intercostals aiding expiration. Intercostal muscle strains can cause pain and difficulty breathing, and may take a long time to heal.
| Characteristics | Values |
|---|---|
| Number of Intercostal Spaces | 11 |
| Number of Intercostal Muscle Groups | 3 |
| Superficial to Deep Muscle Groups | External, Internal, Innermost |
| Function of External Intercostals | Elevate the ribs during forced inspiration |
| Function of Internal Intercostals | Depress the ribs during forced expiration |
| Function of Innermost Intercostals | Assist in the depression of ribs during forced expiration |
| Blood Supply to External Intercostals | Anterior and Posterior Intercostal Arteries |
| Blood Supply to Internal and Innermost Intercostals | Anterior and Posterior Intercostal Arteries, Costocervical Trunk, Internal Thoracic and Musculophrenic Arteries |
| Innervation | Intercostal Nerves (T1-T11) |
| Attachments | Originate from the inferior margin of the rib above and attach to the superior border of the rib below |
| Actions | Stabilise the position of the ribs during normal respiration |
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What You'll Learn
Intercostal muscles have three layers: external, internal, and innermost
The intercostal muscles are a group of intrinsic rib cage muscles occupying the 11 intercostal spaces. They are divided into three groups, from superficial to deep: external, internal, and innermost.
The external intercostals are the most superficial intercostal muscles. They originate from the inferior border of one rib, course inferomedially, and insert 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 blood supply to the external intercostals comes from the anterior and posterior intercostal arteries. The function of the external intercostal muscles is to elevate the ribs during 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 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 function of the internal intercostal muscles is to depress the ribs during forced expiration, thus decreasing the thoracic volume.
The innermost intercostals are the deepest intercostal muscles. They originate from the costal groove of one rib, posteriorly to the origin of the internal intercostals. They course inferomedially, in the same fashion as the internal intercostals, and insert to the superior border of the immediate rib below. The vascularization and innervation of the innermost intercostals follow the same pattern as for the internal intercostals. The blood supply comes from the anterior and posterior intercostal arteries, costocervical trunk, internal thoracic, and musculophrenic arteries. The function of the innermost intercostals is to assist in the depression of ribs during forced expiration.
All three groups of muscles support the rib cage and are accessory respiratory muscles that participate in the process of forced breathing.
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They occupy the 11 intercostal spaces between the ribs
The intercostal muscles occupy the 11 intercostal spaces between the ribs. They are divided into three groups: the external intercostals, the internal intercostals, and the innermost intercostals. These muscles support the rib cage and assist in forced 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 immediate rib below. They run inferoanteriorly from the rib above to the rib below and are continuous with the external oblique of the abdomen. The function of the external intercostals is to elevate the ribs during forced inspiration, increasing the thoracic volume.
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. They extend from the rib above to the one below but in the opposite direction to the external intercostals (inferoposteriorly). They are continuous with the internal oblique muscle of the abdominal wall. The function of the internal intercostals is to depress the ribs during forced expiration, decreasing the thoracic volume.
The innermost intercostals are the deepest intercostal muscles. They originate from the costal groove of one rib, posterior to the origin of the internal intercostals. They are similar in structure to the internal intercostals but are separated from them by the intercostal neurovascular bundle. They are found in the most lateral portion of the intercostal spaces. The function of the innermost intercostals is to assist in depressing the ribs during forced expiration.
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External intercostals facilitate forced inspiration
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 facilitate forced inspiration. They are the most superficial intercostal muscles and are located superficially to the internal intercostal muscles. The external intercostal muscles elevate the ribs during forced inhalation, increasing the thoracic volume. They originate from the inferior border of one rib, course inferomedially, and insert to the superior border of the immediate rib below. The external intercostal muscles consist of 11 pairs of muscles, and each muscle occupies its intercostal space. They are functionally classified as accessory respiratory musculature.
The internal intercostal muscles, on the other hand, aid in forced expiration. They are the middle layer of the intercostal musculature and are located deep to the external intercostals. They originate from the costal groove of one rib and insert to the superior border of the immediate rib below. The internal intercostal muscles help depress the ribs during forced expiration, decreasing the thoracic volume.
The innermost intercostals are the deepest intercostal muscles and are similar in structure to the internal intercostals. They assist in the depression of ribs during forced expiration. They originate from the costal groove of one rib, posteriorly to the origin of the internal intercostals, and insert to the superior border of the immediate rib below.
Together, the external, internal, and innermost intercostal muscles support the rib cage and play a crucial role in forced breathing. The external intercostals, in particular, facilitate forced inspiration by elevating the ribs and increasing the thoracic volume.
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Internal and innermost intercostals aid forced expiration
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 during inhalation, increasing the thoracic volume.
The internal and innermost intercostals aid forced expiration. The internal intercostals form the middle layer of the intercostal musculature. They originate from the inferior margin of costal cartilage and inner lip of the costal groove and insert to the superior border of the immediate rib below. They are located deep to the external intercostals and are separated from them by a thin fascia. The internal intercostals depress the ribs during forced expiration, decreasing the thoracic volume.
The innermost intercostals are the deepest intercostal muscles. They originate from the costal groove of one rib, posteriorly to the origin of the internal intercostals. They have a similar structure to the internal intercostals but are located in the most lateral portion of the intercostal spaces. The innermost intercostals assist in depressing the ribs during forced expiration, working alongside the internal intercostals to shrink the diameter of the thoracic cavity.
To remember the function of the internal and innermost intercostals in forced expiration, it may be helpful to associate their role with the action of depressing the ribs and reducing the thoracic volume. This is in contrast to the external intercostals, which elevate the ribs during forced inspiration. Additionally, the internal and innermost intercostals are located deeper in the body compared to the more superficial external intercostals.
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Intercostal muscles are accessory respiratory muscles
The intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces. They are divided into three groups, namely 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 to the superior border of the immediate rib below. The function of the external intercostal muscles is to elevate the ribs during 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 to the superior border of the immediate rib below. The internal intercostal muscles are the accessory respiratory muscles. They depress the ribs during forced expiration, thus shrinking the diameter of the thoracic cavity.
The innermost intercostals are the deepest intercostal muscles. They originate from the costal groove of one rib, posteriorly to the origin of the internal intercostals. They course inferomedially, in the same fashion as the internal intercostals, and insert to the superior border of the immediate rib below. The function of the innermost intercostals is to assist in the depression of ribs during forced expiration.
Deficient intercostal muscles may not provide appropriate tension to the intercostal spaces, leading to internal and external movements of the chest wall during thoracic pressure changes and resulting in respiratory insufficiency.
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Frequently asked questions
Intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces. They are divided into three groups: external intercostals, internal intercostals, and innermost intercostals. All three groups support the rib cage and are accessory respiratory muscles.
The function of the external intercostal muscles is to elevate the ribs during forced inspiration.
The internal intercostal muscles depress the ribs during forced expiration, thereby decreasing the thoracic volume.
